BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from

Beta-blocker treatment during pregnancy and adverse pregnancy outcomes: a nationwide population based cohort study

For peer review only Journal: BMJ Open

Manuscript ID: bmjopen-2012-001185

Article Type: Research

Date Submitted by the Author: 20-Mar-2012

Complete List of Authors: Meidahl Petersen, Kasper; Rigshospitalet, University Hospital Copenhagen, Department of Clinical Pharmacology, Q Jimenez-Solem, Espen; Bispebjerg Hospital, Laboratory of Clinical Pharmacology Andersen, Jon Traerup; Bispebjerg Hospital, Department of Clinical Pharmacology Petersen, Morten; Bispebjerg Hospital, Department of Clinical Pharmacology Brødbæk, Kasper; Bispebjerg Hospital, Department of Clinical Pharmacology; Rigshospitalet, Laboratory of Clinical Pharmacology Poulsen, Henrik; Bispebjerg Hospital, Department of Clinical Pharmacology; Rigshospitalet, Laboratory of Clinical Pharmacology K�ber, Lars; Rigshospitalet, Department of Cardiology http://bmjopen.bmj.com/ Torp-Pedersen, Christian; Gentofte Hospital, Department of Cardiology

Primary Subject Pharmacology and therapeutics Heading:

Secondary Subject Heading: Epidemiology, Evidence based practice

CLINICAL PHARMACOLOGY, Maternal medicine < OBSTETRICS, Keywords:

EPIDEMIOLOGY on September 26, 2021 by guest. Protected copyright.

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 1 of 22 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 Beta-blocker treatment during pregnancy and adverse pregnancy outcomes: a nationwide 5 population-based cohort study 6 7 8 9 Kasper Meidahl Petersen MB1; Espen Jimenez-Solem MD1; Jon Trærup Andersen MD1; 10 11 Morten Petersen MD1, PhD; Kasper Brødbæk MD1; Henrik Enghusen Poulsen MD, DMSc1; 12 13 Lars Køber MD, DMSc2; Christian Torp-Petersen MD, DMSc3 14 15 For peer review only 16 17 18 Author affiliations 19 20 1: Department of Clinical Pharmacology, Q, Rigshospitalet, University Hospital Copenhagen, 21 22 Denmark 23 24 25 2: Department of Cardiology, Rigshospitalet, University Hospital Copenhagen, Denmark 26 27 3: Department of Cardiology, Gentofte Hospital, Gentofte, Denmark 28 29 30 31 Keywords (MeSH): Adrenergic beta-antagonists, pregnancy, small for gestational age infant, 32 premature birth, perinatal mortality. 33 http://bmjopen.bmj.com/ 34 35 Words: 2995 36 37 38 Correspondence to: 39 Kasper Meidahl Petersen 40 Department of Clinical Pharmacology, Q

41 Rigshospitalet, University Hospital Copenhagen on September 26, 2021 by guest. Protected copyright. 42 Tagensvej 20 43 DK-2200 Copenhagen N 44 Denmark 45 46 Tel +45 5123 7716 47 Fax +45 3545 2745 48 E-mail: [email protected] 49 50 51 52 53 54 55 56 57 58 59 1 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 2 of 22 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 5 6 ABSTRACT 7 8 Objective: To investigate the association between exposure to beta-blockers during pregnancy and 9 10 11 the risk of being born small for gestational age (SGA), preterm birth, and perinatal mortality in 12 13 a nationwide cohort. 14 15 Design: A population-basedFor peer retrospective cohortreview study, using the Danishonly Fertility Database. We 16 17 identified all pregnant women redeeming a prescription for beta-blockers using the National 18 19 20 Prescription Registry. Multivariate logistic regression models were used to assess the association 21 22 between exposure and our outcomes. 23 24 Setting: Register based survey. 25 26 Participants: 911685 births between 1995 and 2008 obtained from the Danish Fertility Database. 27 28 Outcome measures: Being born SGA was defined as having a birth weight below the tenth 29 30 th 31 percentile for the corresponding gestational week. Preterm birth was defined as birth before the 37 32

33 gestational week. Perinatal mortality was defined as either death occurring within the first 28 days http://bmjopen.bmj.com/ 34 35 of life, or stillbirth. Before 2004, foetal deaths were recorded as stillbirths if they occurred after 28 36 37 weeks of gestation, but since then stillbirth is recorded for deaths after 22 gestational weeks. 38 39 40 Results: We identified 2459 pregnancies exposed to beta-blockers. Beta-blocker exposure during

41 on September 26, 2021 by guest. Protected copyright. 42 pregnancy was found to be associated with increased risk of SGA; adjusted OR=1.97 (95% CI, 43 44 1.75–2.23), preterm birth; adjusted OR=2.26 (95% CI, 2.03–2.52) and perinatal mortality; adjusted 45 46 OR=1.89 (95 % CI, 1.25–2.84). Analyses were adjusted for socio-economic and maternal variables. 47 48 We found similar risk profiles for pregnancies exposed to labetalol and for pregnancies exposed to 49 50 51 other beta-blockers. 52 53 Conclusion: We found that exposure to beta-blockers during pregnancy was associated with being 54 55 born SGA, preterm birth and perinatal mortality. Our findings show that labetalol is not safer than 56 57 58 59 2 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 3 of 22 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 other beta-blockers during pregnancy, and future treatment of pregnant women with beta-blockers 5 6 should therefore be based primarily on the individual needs of the mother and not the unborn child. 7 8 9 ARTICLE SUMMARY 10 11 12 Article focus 13 14 • There is contradictory evidence concerning the consequences of beta-blocker treatment 15 For peer review only 16 during pregnancy. 17 18 • This survey explores the effects of beta-blocker exposure during pregnancy in a Danish birth 19 20 21 cohort comprising all births in Denmark between 1995 and 2008. In addition we compared 22 23 risks associated with exposure to labetalol with exposure to other beta-blockers. 24 25 Key messages 26 27 • Redeeming prescriptions of beta-blockers was found to be significantly associated with 28 29 increased risk of being born SGA, preterm birth, and perinatal mortality. 30 31 32 • We found comparable risk profiles in labetalol-exposed pregnancies and in pregnancies

33 http://bmjopen.bmj.com/ 34 exposed to any other beta-blocker. 35 36 Strengths and limitations of this study 37 38 39 • This study is the largest of its kind to date, and covers an entire nation which minimises risk 40 of selection bias.

41 on September 26, 2021 by guest. Protected copyright. 42 43 • Given the study design, we were not able to adjust for treatment indication and severity of 44 45 maternal disease, nor were we able to rule out confounding by indication, the underlying 46 47 maternal disease, as a possible explanation for our findings. 48 49 50 51 52 53 INTRODUCTION 54 55 56 57 58 59 3 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 4 of 22 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 Beta-blockers are widely used in the treatment of chronic hypertension,[1-4] migraine,[5] essential 5 6 tremor[6], and various other conditions. There is contradictory evidence concerning the 7 8 consequences of beta-blocker treatment during pregnancy. Some studies report an association 9 10 11 between beta-blocker treatment and small for gestational age (SGA) newborns, and preterm 12 13 birth,[4,7-10] while others do not.[2,11] Preterm birth and being born SGA are both associated with 14 15 increased risk ofFor perinatal mortality.[12,13]peer reviewWe set out to investigate only whether the use of beta- 16 17 blockers during pregnancy was associated with being born SGA, preterm birth and perinatal 18 19 20 mortality in a nationwide survey between 1995 and 2008. 21 22 23 24 METHOD 25 26 Study population 27 28 We used data obtained from three nationwide registries: the Danish Fertility Database,[14] the 29 30 31 Danish National Hospital Register[15], and the National Prescription Register.[16] Data concerning 32

33 income and educational level were obtained respectively from the Income Statistics Register[17] http://bmjopen.bmj.com/ 34 35 and the Danish Education register,[18] both of which are provided by Statistics Denmark. In 36 37 Denmark all citizens are given a unique ten-digit identification number at birth.[19] This number 38 39 40 can be used to link information between nationwide registers.

41 on September 26, 2021 by guest. Protected copyright. 42 Using the Danish Fertility Database we identified 974 805 births between 1995 and 2008. We 43 44 removed 52 603 records lacking information on pregnancy duration and 7681 records with coding 45 46 errors. In addition, we excluded 2836 records with pregnancy-induced hypertension, defined as 47 48 having redeemed an antihypertensive drug prescription after the twentieth week of gestation, but 49 50 51 never before. The final study population thus comprised 911 685 births. 52 53 The Danish Fertility Database contains information on maternal age, date of birth, and 54 55 previous births, as well as on each child’s sex, gestational age, weight, and mortality.[14] 56 57 58 59 4 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 5 of 22 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 Time of conception is based on ultrasound estimates in early pregnancy, or information on last 5 6 menstrual period. 7 8 Information on redeemed prescriptions was retrieved from the National Prescription Register, 9 10 11 which holds information on date of redemption, quantity, strength, and form.[16] Drugs are coded 12 13 in accordance with the Anatomical Therapeutic Chemical (ATC) classification. 14 15 The DanishFor National Hospitalpeer Register review contains information onlyon diagnoses of somatic 16 17 admissions and outpatients at all Danish hospitals since 1977[15] in accordance with the Danish 18 19 20 revision of the 10th International Classification of Diseases (ICD)-system. Pre-eclampsia and 21 22 eclampsia were defined as women diagnosed with O13, O14, or O15. Migraine was defined as G43 23 24 or G44, essential tremor as G250 and arrhythmias as I47, I48, and I49. Maternal smoking was 25 26 defined as women diagnosed with UT00, UT20, UT21, UT22, and UT23. 27 28 29 30 31 Identification of Exposure 32

33 We defined exposure to beta-blockers as the redemption of at least two prescriptions between six http://bmjopen.bmj.com/ 34 35 months before conception and the twentieth week of gestation. At least one of these prescriptions 36 37 38 had to be redeemed between conception and the twentieth week of gestation. 39 40 We assessed exposure to beta-blockers by identifying redeemed prescriptions with ATC code C07.

41 on September 26, 2021 by guest. Protected copyright. 42 Furthermore, we identified the most frequently redeemed beta-blockers in Denmark: labetalol 43 44 (C07AG01), metoprolol (C07AB02), atenolol (C07AB03), propranolol (C07AA05), pindolol 45 46 47 (C07AA03), and sotalol (C07AA07). Fewer than 50 pregnancies were exposed to any of the 48 49 remaining beta-blockers. 50 51 We divided beta-blocker exposure into exposure to labetalol and exposure to other beta- 52 53 blockers. The latter group was formed because there were few redeemed prescriptions of individual 54 55 beta-blockers other than labetalol. We compared risks associated with exposure to beta-blockers 56 57 58 59 5 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 6 of 22 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 with exposure to methyldopa (C02AB01, C02AB02), calcium channel blockers (C08C), and ACE 5 6 inhibitors (C09A) to assess possible confounding by indication. 7 8 Maternal diabetes mellitus was defined as redeeming a prescription for insulin or an insulin 9 10 11 analogue (ATC code A10A). Furthermore, we assessed co-medication with statins (ATC code C10) 12 13 and antiobesity drugs (ATC code A08A). We identified pregnant women redeeming prescriptions 14 15 with these drugsFor in order to adjustpeer for diabetes review mellitus, obesity, andonly statin use since these women 16 17 have different risk profiles for the defined outcomes. 18 19 20 21 22 Definition of Outcomes 23 24 Being born SGA was defined as having a birth weight below the tenth percentile for the 25 26 th 27 corresponding gestational week. Preterm birth was defined as birth before the 37 gestational week. 28 29 Perinatal mortality was defined as either death occurring within the first 28 days of life, or stillbirth. 30 31 Before 2004, foetal deaths were recorded as stillbirths if they occurred after 28 weeks of gestation, 32

33 but since then stillbirth is recorded for deaths after 22 gestational weeks.[20] http://bmjopen.bmj.com/ 34 35 36 37 38 Statistical analyses 39 40 Data were managed and analysed using SAS 9.2 (SAS Institute Inc., Cary, NC, USA). Logistic

41 on September 26, 2021 by guest. Protected copyright. 42 regression models were developed for dichotomous variables adjusted for maternal age, year of 43 44 45 conception, annual household income, parity, and educational level (model 1). Maternal age was 46 47 divided into five groups: <20, 21-25, 26-30, 31-35, >35 years (no missing values). Annual 48 49 household income at year of birth was divided into quartiles (1266 missing values). Subjects were 50 51 divided into quartiles according to the number of previous births, including stillbirths (37 missing 52 53 ≥ 54 values): 0, 1, 2, 3 births. Year of conception was ordered into three categories (1994-1998, 1999- 55 56 2003, and 2004-2008). Educational level was divided into tertiles by highest level of education 57 58 59 6 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 7 of 22 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 achieved at the year of birth. For missing information we used information from the following 5 6 calendar year (32 745 missing values). 7 8 We constructed a separate logistic regression model (model 2) including the socio-economic 9 10 11 variables in model 1 and additional confounding variables: smoking status, co-medication (yes/no) 12 13 with statins, antiobesity drugs, insulin and insulin analogues, and diagnoses of pre- 14 15 eclampsia/eclampsia.For These peerconfounders were review included in model 2only due to the high frequency of 16 17 missing data, because information on smoking and diagnoses of pre-eclampsia/eclampsia were not 18 19 20 available for the years 1995 and 2008. Maternal smoking was divided into four categories according 21 22 to the number of cigarettes smoked daily (0, 1-10, 11-20, >20). 23 24 When estimating the risk of perinatal mortality, analyses were further adjusted for previous 25 26 stillbirths. Odds ratios are presented with 95% confidence intervals (95% CIs). For description of 27 28 basic characteristics we used frequencies with percentages. We used Chi-square tests to analyse 29 30 31 differences in the proportions of the different classes of categorical baseline characteristics. 32

33 Statistical significance was defined as p<0.05. All tests were two-sided. http://bmjopen.bmj.com/ 34 35 In addition, we carried out a propensity score-matched regression analysis to consolidate our 36 37 findings. We calculated a propensity score for the likelihood of redeeming a beta-blocker during 38 39 40 pregnancy by multivariate logistic regression conditional on baseline covariates. Using the Greedy

41 on September 26, 2021 by guest. Protected copyright. 42 matching macro (http://mayoresearch.mayo.edu/mayo/research/biostat/upload/gmatch.sas), we 43 44 matched each case to four controls on the basis of the propensity score (table 1). We did not match 45 46 on diagnoses of pre-eclampsia/eclampsia since a large fraction of these cases redeemed beta-blocker 47 48 prescriptions. 49 50 51 52 53 54 RESULTS 55 56 57 58 59 7 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 8 of 22 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 Table 1 presents maternal characteristics in beta-blocker-exposed and unexposed women (number 5 6 and percentage of pregnancies). We identified 2381 pregnancies exposed to only one beta-blocker, 7 8 1452 exposed to labetalol only, and 929 exposed to other beta-blockers. 98 pregnancies were 9 10 11 exposed to more than one beta-blocker. We found 515 pregnancies exposed to methyldopa, 86 12 13 pregnancies to calcium channel blockers (CCBs), and 48 pregnancies exposed to ACE inhibitors. 14 15 Women exposedFor to beta-blockers peer during pregnancy review were older, had only higher income, and higher 16 17 parity than unexposed women. The proportions of women redeeming prescriptions for statins, 18 19 20 antiobesity preparations, and insulins were higher among the beta-blocker-exposed group. The 21 22 proportion of pregnancies complicated by pre-eclampsia was higher among beta-blocker-exposed 23 24 pregnancies. There was no difference in smoking prevalence between beta-blocker-exposed and 25 26 unexposed women (table 1). 27 28 29 30 31 32

33 http://bmjopen.bmj.com/ 34 35 36 37

38 39

40

41 on September 26, 2021 by guest. Protected copyright. 42 43 44 45 46 47 48 49 50 51 52 Beta-blocker-exposed Beta-blocker-unexposed Propensity matched 53 54 Table 1. Basic characteristics for pregnancies exposed to beta-blockers, compared with unexposed 55 pregnancies and propensity score-matched pregnancies. 56 (n=2459) (n=909228) (n=9662) 57 58 59 8 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 9 of 22 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 Characteristics n (%) n (%) p-valuea n (%) p-valuea 5 Educational level <0.001 0.991 6 Low 739 (30.05) 311 600 (35.45) 2965 (30.69) 7 8 Medium 972 (39.53) 285 450 (32.47) 3883 (40.19) 9 High 707 (28.75) 279 431 (31.79) 2814 (29.12) 10 Annual household income (GBP) <0.001 0.989 11 0- 36 770 509 (23.99) 226 228 (24.84) 1924 (19.91) 12 36 771 – 52 703 594 (24.16) 227 195 (24.96) 2337 (24.19) 13 52 704 – 74 699 662 (26.92) 227 089 (24.94) 2631 (27.23) 14 ≥ 74 700 693 (28.18) 227 448 (24.98) 2770 (28.67) 15 For peer review only 16 Parity <0.001 0.998 17 1 900 (36.60) 394 661 (43.29) 3487 (28.87) 18 2 918 (37.33) 338 989 (37.18) 3658 (30.28) 19 3 455 (18.50) 129 482 (14.20) 1788 (14.80) 20 >3 186 (7.56) 46 057 (5.05) 729 (6.04) 21 Age (years) <0.001 1.000 22 <20 18 (0.73) 26 321 (2.89) 68 (0.56) 23 24 21-25 174 (7.07) 147 298 (16.16) 699 (5.79) 25 26-30 700 (28.47) 350 105 (38.40) 2757 (22.82) 26 31-35 930 (37.82) 281 154 (30.84) 3665 (30.34) 27 >35 637 (24.90) 104 339 (11.44) 2473 (20.47) 28 Daily cigarettesb 0.427 0.385 29 0 1548 (80.29) 572 642 (81.15) 6140 (81.81) 30 1-10 251 (13.02) 90 033 (12.76) 913 (12.16) 31 32 11-20 114 (5.19) 36201 (5.13) 394 (5.25)

33 >20 15 (0.78) 4849 (0.69) 59 (0.79) http://bmjopen.bmj.com/ 34 Statins <0.001 0.492 35 Used 5 (0.20) 111 (0.01) 14 (0.14) 36 Not used 2454 (99.8) 909 115 (99.99) 9648 (99.86) 37 38 Antiobesity preparations (A10) 0.018 0.251 39 Used 9 (0.40) 1539 (0.17) 23 (0.24) 40 Not used 2450 (99.6) 907 687 (99.83) 9639 (99.76)

41 on September 26, 2021 by guest. Protected copyright. Insulins and analogues 42 <0.001 0.782 43 Used 101 (4.11) 4208 (0.46) 412 (4.14) 44 Not used 2358 (95.89) 905 018 (99.53) 9250 (95.74)

45 Pre-eclampsia (O13-O15) <0.001 46 Yes 99 (4.03) 7806 (0.86) - 47 48 No 2360 (95.97) 901 420 (99.14) - 49 50 aChi-square tests were used to assess the overall p value for the group comparison. 51 52 bInformation on smoking was only available for 1996-2007. 53 54 55 56 57 58 59 9 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 10 of 22 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 Women redeeming labetalol prescriptions were older, had a higher education level, and a 5 6 higher prevalence of preeclampsia and smoking than women exposed to other beta-blockers (table 7 8 2). The proportion of women redeeming prescriptions for insulin was larger among the labetalol- 9 10 11 exposed group. There was no difference in income or co-medication with statins and antiobesity 12 13 preparations between the two groups. Diagnoses of migraine and arrhythmias were more common 14 15 among women exposedFor to anypeer other beta-blocker. review Women exposed only to other beta-blockers had 16 17 higher parity than those exposed to labetalol. 18 19 20 Table 2. Basic characteristics for pregnancies exposed to labetalol, 21 compared with pregnancies exposed to other beta-blockers. 22 23 24 Labetalol Other beta-blockers 25 (n=1452) (n=929) 26 a 27 Characteristics n (%) n (%) p-value 28 Educational level <0.001 29 Low 391 (26.93) 321 (34.55) 30 Medium 571 (39.33) 369 (39.72) 31 32 High 462 (31.82) 226 (24.33)

33 Annual household income (GBP) 0.138 http://bmjopen.bmj.com/ 34 0 – 36 770 202 (13.91) 289 (31.11) 35 36 771 – 52 703 223 (15.36) 357 (38.43) 36 37 52 704 – 74 699 228 (15.70) 413 (44.46) 38 ≥74 700 275 (19.94) 393 (42.30) 39 Parity 0.004 40 0 512 (35.26) 363 (39.07)

41 on September 26, 2021 by guest. Protected copyright. 42 1 586 (40.36) 308 (33.15) 43 2 256 (17.63) 179 (19.27) 44 ≥3 98 (6.75) 79 (8.50) 45 46 Age (years) <0.001 47 <20 7 (0.58) 10 (1.08) 48 21-25 69 (4.75) 97 (10.44) 49 26-30 406 (27.96) 275 (29.60) 50 51 31-35 586 (40.36) 314 (33.79) 52 >35 384 (26.45) 233 (25.08) 53 Daily cigarettesb <0.001 54 55 0 933 (64.26) 565 (60.82) 56 1-10 130 (8.95) 112 (12.06) 57 11-20 44 (3.03) 62 (6.67) 58 59 10 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 11 of 22 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 >20 9 (6.19) 6 (0.65) 5 Antiobesity drugs 0.052 6 7 Yes 5 (0.34) 9 (0.97) 8 No 1447 (99.66) 920 (99.03) 9 Statins 0.261 10 11 Yes 5 (0.34) 1 (0.10) 12 No 1447 (99.66) 928 (99.90) 13 Insulins and analogues <0.001 14 Yes 1369 (5.72) 16 (1.72) 15 For peer review only 16 No 83 (94.28) 913 (92.28) 17 Migraine <0.001 18 Yes 26 (1.79) 46 (4.95) 19 No 1426 (98.21) 883 (95.05) 20 21 Pre-eclampsia 0.001 22 Yes 1378 (94.90) 908 (97.84) 23 No 74 (5.10) 21 (2.26) 24 25 Arrhythmia <0.001 26 Yes 23 (1.58) 82 (8.83) 27 No 1429 (98.42) 847 (91.17) 28 Essential tremor 0.030 29 30 Yes - 3 (0.33) 31 No 1452 (100) 926 (99.67) 32 a 33 Chi square tests were used to assess the overall p value for the group http://bmjopen.bmj.com/ 34 comparison. 35 36 bInformation on smoking was only available for 1996-2007. 37 38 39 40 Table 3 presents ORs with 95% CIs for SGA, preterm birth and perinatal death for exposure

41 on September 26, 2021 by guest. Protected copyright. 42 to beta-blockers during pregnancy. 43 44 45 46 47 SGA 48 49 We found 93 662 children born SGA in the unexposed population (table 3). There were 446 50 51 children born SGA among pregnancies exposed to some kind of beta-blocker. We found a higher 52 53 proportion of SGA among women exposed to beta-blockers compared with unexposed women. 54 55 56 57 58 59 11 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 12 of 22 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 Women exposed to labetalol or to other beta-blockers had similarly higher odds ratios than 5 6 unexposed women (table 3). 7 8 9 10 11 Preterm birth 12 13 We identified 109 163 preterm births in the unexposed population (table 3). There were 697 preterm 14 15 births among pregnanciesFor exposedpeer to beta-blockers. review We found an associationonly between preterm birth 16 17 18 and beta-blocker exposure compared with unexposed women. Those exposed to labetalol or to other 19 20 beta-blockers had similarly higher odds ratios than unexposed women (table 3). 21 22 23 24 25 Perinatal mortality 26 27 We identified 6048 perinatal deaths in the unexposed population (table 3). There were 44 perinatal 28 29 deaths among infants exposed to beta-blockers. We found a higher rate of perinatal mortality 30 31 amongst women exposed to beta-blockers (table 3). 32

33 http://bmjopen.bmj.com/ When stratifying for different beta-blockers we found 30 perinatal deaths among labetalol- 34 35 36 exposed pregnancies. Labetalol exposure was associated with increased risk of perinatal mortality 37 38 (table 3). 39 40 We identified 13 perinatal deaths among pregnancies exposed to other beta-blockers.

41 on September 26, 2021 by guest. Protected copyright. 42 Exposure to other beta-blockers was found to be significantly associated with perinatal mortality in 43 44 45 the unadjusted model and model 1. However, adjusting our analysis for additional confounding 46 47 variables (Model 2) rendered the association statistically insignificant (table 3). 48 49 50 51 52 Other analyses 53 54 We identified 515 pregnancies exposed to methyldopa (table 3). We found 61 children born SGA, 55 56 216 preterm births and 4 perinatal deaths among these pregnancies. We found a positive association 57 58 59 12 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 13 of 22 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 between children born SGA and exposure to methyldopa, and between methyldopa exposure and 5 6 increased risk of preterm birth. Exposure to methyldopa during pregnancy was not significantly 7 8 associated with perinatal mortality (table 3). 9 10 11 12 13 Table 3. ORs with 95% CIs for SGA, preterm birth and perinatal death for exposure to beta- 14 15 blockers duringFor pregnancy. peer review only 16 17 18 19 Exposure Crude Adjusted (model 1) Adjusted (model 2) 20 N (%) OR (95% CI) OR (95% CI) OR (95% CI) 21 SGA 22 23 Unexposed (n=909 226) 93 662 (10.30) Reference Reference Reference 24 All beta-blockers (n=2459) 446 (18.14) 1.93 (1.74-2.14) 1.99 (1.79-2.21) 1.97 (1.75-2.23) 25 Labetalol only (n=1452) 258 (17.77) 1.88 (1.64-2.15) 1.95 (1.70-2.24) 2.02 (1.72-2.37) 26 Other beta-blockers (n=929) 179 (19.27) 2.08 (1.76-2.44) 2.11 (1.79-2.49) 2.01 (1.66-2.43) 27 28 Methyldopa (n= 515) 61 (11.84) 1.17 (0.89-1.53) 1.32 (1.01-1.73) 1.43 (1.04-1.96) 29 CCBs (n=86) 21 (24.42) 2.30 (1.42-3.73) 2.24 (1.36-3.67) 1.88 (1.02-3.49) 30 31 32 Preterm birth

33 Unexposed (n=909 226) 109 163 (12.01) Reference Reference Reference http://bmjopen.bmj.com/ 34 All beta-blockers (n=2459) 697 (28.34) 2.9 (2.66-3.14) 2.71 (2.48-2.97) 2.26 (2.03-2.52) 35 Labetalol only (n=1452) 473 (32.58) 3.54 (3.17-3.95) 3.33 (2.98-3.72) 2.74 (2.39-3.13) 36 37 Other beta-blockers (n=929) 206 (22.17) 2.08 (1.78-2.43) 1.93 (1.65-2.26) 1.69 (1.41-2.03) 38 Methyldopa (n= 515) 216 (41.94) 5.29 (4.44-6.31) 5.03 (4.21-6.01) 4.21 (3.38-5.23) 39 CCBs (n=86) 26 (30.23) 2.55 (1.63-3.99) 2.50 (1.60-3.89) 2.15 (1.26-3.67) 40

41 on September 26, 2021 by guest. Protected copyright. 42 Perinatal mortality 43 Unexposed (n=909 226) 6048 (0.67) Reference Reference Reference 44 All beta-blockers (n=2459) 44 (1.79) 2.72 (2.02-3.67) 2.69 (1.98-3.65) 1.89 (1.25-2.84) 45 46 Labetalol only (n=1452) 30 (2.07) 3.15 (2.19-4.52) 3.24 (2.25-4.67) 2.08 (1.26-3.44) 47 Other beta-blockers (n=929) 13 (1.39) 2.12 (1.22-3.66) 1.92 (1.08-3.40) 1.72 (0.85-3.48) 48 Methyldopa (n= 515) 4 (0.78) 1.15 (0.43-3.07) 1.16 (0.43-3.12) 0.35 (0.05-2.50) 49 CCBs (n=86) 1 (1.16) 1.78 (0.25-12.57) 2.00 (0.28-14.83) 3.26 (0.45-23.77) 50 51 52 Analyses are adjusted for maternal age, household income, educational level, parity, birth year and prior stillbirths. 53 aModel 2 is furthermore adjusted for smoking and comedication with statins, antiobesity preparations, insulins and 54 diagnoses of pre-eclampsia/eclampsia. The cohort in model 2 comprises all births between 1996 and 2007 (n=778

55 394). 56 57 58 59 13 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 14 of 22 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 We found 86 pregnancies exposed to calcium channel blockers (table 3). These included 17 5 6 children born SGA, 18 preterm births and 1 perinatal death. We found an association between 7 8 exposure to calcium channel blockers and children born SGA in all models. 9 10 11 Additionally, we found an association between exposure to calcium channel blockers and 12 13 increased risk of preterm birth in all models. As with methyldopa, exposure to calcium channel 14 15 blockers duringFor pregnancy waspeer not found to review be associated with perinatal only mortality (table 3). 16 17 Analyses for exposure to ACE inhibitors were not performed since we identified only 48 18 19 20 pregnancies exposed to them. 21 22 Post hoc we analysed the effect of exposure to all beta-blockers using a propensity score- 23 24 matched control group (Table 1) and found similar results to those of the primary analyses: SGA, 25 26 OR=1.93 (95% CI, 1.71–2.19); preterm birth, OR=2.40 (95% CI, 2.16–2.67); perinatal mortality, 27 28 OR=3.22 (95% CI, 2.15–4.82). 29 30 31 32

33 DISCUSSION http://bmjopen.bmj.com/ 34 35 In the present study, which we believe to be the largest of its kind to date, we found an association 36 37 between redeeming prescriptions of beta-blockers during pregnancy and being born SGA, preterm 38 39 40 birth, and perinatal mortality. In addition, we found an association between redeeming prescriptions

41 on September 26, 2021 by guest. Protected copyright. 42 of methyldopa and calcium channel blockers, being born SGA, and preterm birth. Methyldopa and 43 44 calcium channel blockers were not found to be associated with perinatal mortality. 45 46 We found exposure to any beta-blocker to be associated with being born SGA. Our results are 47 48 in accordance with a recent study reporting increased risk of being born SGA among pregnancies 49 50 51 exposed to selective beta-blockers (OR=6.00; 95% CI, 1.06–33.87) and labetalol (OR=2.26; 95% 52 53 CI, 1.04–4.88).[9] Labetalol is generally considered safe for use during pregnancy.[1,8,21] 54 55 56 57 58 59 14 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 15 of 22 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 Exposure to beta-blockers was found to be associated with preterm birth. When stratifying for 5 6 different beta-blockers we found an increased risk of preterm birth after exposure to labetalol, and 7 8 all other beta-blockers, respectively. 9 10 11 We found an association between exposure to beta-blockers and perinatal mortality. When 12 13 stratifying for different beta-blockers we found this association to be statistically significant for 14 15 exposure to labetalolFor and other peer beta-blockers review. When adjusting our onlyanalysis for maternal co- 16 17 morbidity, co-medication, and smoking, only labetalol was found to be associated with perinatal 18 19 20 mortality. 21 22 Methyldopa is mainly used to treat chronic hypertension during pregnancy as first-line 23 24 therapy.[1] Previous studies did not find any associations between methyldopa exposure and being 25 26 born SGA or preterm birth.[1,3] Methyldopa has not been found to have effects on placental 27 28 haemodynamics.[1] However, a recent case-control study reported an increased risk of being born 29 30 31 SGA among pregnancies exposed to centrally acting adrenergic agents during the second and third 32

33 trimesters[9]: OR=1.70 (95% CI, 1.00–2.89). We found that methyldopa exposure was associated http://bmjopen.bmj.com/ 34 35 with being born SGA and preterm birth. This could be due to indicative antihypertensive treatment 36 37 with methyldopa in pregnant women with diabetes or pregnancy related diabetes. The prevalence of 38 39 40 diabetes among methyldopa-exposed pregnancies was found to be higher: 11.1% compared with

41 on September 26, 2021 by guest. Protected copyright. 42 3.9% among beta-blocker-exposed pregnancies. Increased risk of preterm birth was still seen after 43 44 adjusting our analyses for additional confounding variables in model 2. We found no association 45 46 between exposure to methyldopa and perinatal mortality. These findings are consistent with those of 47 48 a previous study.[3] 49 50 51 Calcium channel blockers are considered to be safe during pregnancy.[3,22] We found that 52 53 exposure to calcium channel blockers was associated with being born SGA and with preterm birth. 54 55 The risk of being born SGA and preterm of birth remained after adjusting our analyses for 56 57 58 59 15 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 16 of 22 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 additional confounding variables in model 2. We found no statistically significant association 5 6 between calcium channel blocker exposure during pregnancy and perinatal mortality. 7 8 We chose to analyse two outcomes previously reported to be associated with beta-blocker 9 10 11 exposure during pregnancy —SGA and preterm birth[1,10,23] — that have been associated with 12 13 increased perinatal mortality in previous studies.[12,13] Therefore we investigated the risk of 14 15 perinatal mortalityFor among beta-blocker-exposedpeer review pregnancies. We comparedonly risks associated with 16 17 exposure to beta-blockers with exposure to methyldopa and calcium channel blockers to assess 18 19 20 possible confounding by indication. Our analyses show a similar risk of being born SGA and an 21 22 increased risk of preterm birth for all recommended agents during pregnancy. There are various 23 24 possible explanations for this finding. It is possible that the underlying indication for treatment, 25 26 maternal disease, is the true risk factor. Possible maternal diseases include hypertension, either 27 28 predating or complicating pregnancy. Accordingly, we were not able to rule out a potential effect of 29 30 31 maternal disease on perinatal outcomes. 32

33 We found an association between exposure to beta-blockers during pregnancy and perinatal http://bmjopen.bmj.com/ 34 35 mortality. This association was not found for exposure to methyldopa and calcium channel 36 37 blockers, which might be due to the small number of cases. 38 39 40 We believe that the similar risks found for exposure to the various beta-blockers and SGA,

41 on September 26, 2021 by guest. Protected copyright. 42 preterm birth, and perinatal mortality are a class effect. This seems to be true in spite of statistically 43 44 significant differences in the basic characteristics of women exposed to labetalol and those exposed 45 46 to other beta-blockers (table 2). After adjustments were made for these variables, we found 47 48 comparable risk profiles for labetalol-exposed pregnancies and pregnancies exposed to other beta- 49 50 51 blockers. Most beta-blockers are known to cross the placenta,[21,24] and effects on placental 52 53 haemodynamics have been observed in both human and animal studies. A mechanism has been 54 55 proposed of diminished placental blood flow due to the selective vasoconstriction of placental 56 57 58 59 16 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 17 of 22 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 vessels by beta-blockers without intrinsic sympathomimetic activity.[24] This effect on placental 5 6 haemodynamics could explain growth retardation of foetuses exposed to beta-blockers during 7 8 pregnancy and might result in children being born SGA and preterm. 9 10 11 We defined exposure as redemption of at least two prescriptions between six months before 12 13 conception and the twentieth week of gestation. At least one of these prescriptions had to be 14 15 redeemed betweenFor conception peer and twentieth review week of gestation. We only believe that this model 16 17 increases the probability of identifying continuous use that extends into pregnancy. 18 19 20 The rate of perinatal mortality in Denmark is low (table 3).[25] A large number of women 21 22 exposed to beta-blockers, methyldopa, and calcium channel blockers are therefore needed to 23 24 identify a possible risk increase associated with these outcomes. Our cohort comprises all births in 25 26 Denmark between 1995 and 2008. This minimises confounding due to race, educational level, and 27 28 other socio-economic factors. The national Danish registers cover the entire nation and are 29 30 31 considered valid. As part of the national health care reimbursement scheme, Danish pharmacies are 32

33 required by law to register all redeemed prescriptions. Approximately 97.5% of all redeemed http://bmjopen.bmj.com/ 34 35 prescriptions are registered in the Danish Prescription register.[16] Our study includes data on 36 37 exposure to beta-blockers based on information on prescriptions paid for at the pharmacy, and not 38 39 40 only prescribed by the physician, thereby increasing the probability of exposure. Furthermore, our

41 on September 26, 2021 by guest. Protected copyright. 42 study was not confounded by recall bias since information was recorded prospectively. The Danish 43 44 Fertility Database contains more than 99% of all births during the study period.[14] 45 46 Limitations of our study include missing information on maternal weight and alcohol 47 48 consumption. We were unable to adjust for treatment indication and severity of maternal disease. 49 50 51 Given the study design, we were not able to address this issue further, nor were we able to rule out 52 53 confounding by indication, the underlying maternal disease, as a possible explanation for our 54 55 findings. 56 57 58 59 17 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 18 of 22 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 We estimated exposure from National Prescription Registry data, which contains information 5 6 on all redeemed prescriptions.[16] Overestimation of exposure is therefore a possibility, since we 7 8 cannot adjust for a potential lack of compliance. However, in a study by Olesen et al. conducted in a 9 10 11 cohort of pregnant Danish women in the county of North Jutland,[26] compliance with prescribed 12 13 beta-blockers was estimated to be complete, strengthening the validity of our analyses. 14 15 Furthermore, overestimationFor peer of exposure would review bias the estimates onlytowards unity. 16 17 There is a general consensus that labetalol is safer than other beta-blockers during pregnancy 18 19 20 and this drug is rapidly becoming the first-line choice in conditions such as chronic hypertension 21 22 during pregnancy.[21,23] We found an association between redeeming prescriptions for beta- 23 24 blockers and being born SGA, preterm birth, and perinatal mortality. Risk profiles for pregnancies 25 26 exposed to labetalol and to other beta-blockers were similar. Our findings therefore suggest that 27 28 future treatment of pregnant women with beta-blockers should be based primarily on the individual 29 30 31 needs of the mother and not of the unborn child. The increasing use and uncertainty of effects and 32

33 possible side effects of treatment with beta-blockers during pregnancy call for further studies. http://bmjopen.bmj.com/ 34 35 36 37 Conflicts of interests 38 39 40 The authors have no relevant conflict of interests.

41 on September 26, 2021 by guest. Protected copyright. 42 Funding 43 44 The project was sponsored by the Capital Region of Copenhagen. 45 46 Contributorship Statement 47 48 49 KMP, EJS, JTA, MP, KB, LK, CTP, HEP 50 KMP, EJS, JTA and HEP conceptualized the study. MP, KB, LK and CTP assisted with the study 51 design. KMP preformed the analyses assisted by EJS and JTA, MP, KB, LK, CTP and HEP assisted 52 53 in the interpretation. KMP, EJS, JTA, MP, KB, LK, CTP and HEP wrote and revised the final 54 manuscript. Figure design was done by KMP, EJS, JTA, MP, KB, LK, CTP and HEP. All authors 55 approved the final version to be published. 56 57 58 59 18 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 19 of 22 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 5 6 REFERENCES 7 8 9 1 Sibai BM. Treatment of hypertension in pregnant women. N Engl J Med 1996 Jul 10 11 25;335(4):257-65. 12 13 14 2 Magee LA, Ornstein MP, von DP. Fortnightly review: management of hypertension in 15 For peer review only 16 17 pregnancy. BMJ 1999 May 15;318(7194):1332-6. 18 19 20 3 Afifi Y, Churchill D. Pharmacological treatment of hypertension in pregnancy. Curr Pharm 21 22 Des 2003;9(21):1745-53. 23 24 25 4 Magee LA, Duley L. Oral beta-blockers for mild to moderate hypertension during 26 27 28 pregnancy. Cochrane Database Syst Rev 2003;(3):CD002863. 29 30 31 5 Modi S FAU - Lowder D, Lowder DM. Medications for migraine prophylaxis.(0002-838X 32

33 (Print)). http://bmjopen.bmj.com/ 34 35 36 6 Lyons KE FAU - Pahwa R, Pahwa R. Pharmacotherapy of essential tremor : an overview of 37 38 existing and upcoming agents.(1172-7047 (Print)). 39 40

41 on September 26, 2021 by guest. Protected copyright. 42 7 Sibai BM, Gonzalez AR, Mabie WC et al. comparison of labetalol plus hospitalization 43 44 versus hospitalization alone in the management of preeclampsia remote from term. Obstet 45 46 Gynecol 1987 Sep;70(3 Pt 1):323-7. 47 48 49 8 Magee LA, Elran E, Bull SB et al. Risks and benefits of beta-receptor blockers for 50 51 pregnancy hypertension: overview of the randomized trials. Eur J Obstet Gynecol Reprod 52 53 54 Biol 2000 Jan;88(1):15-26. 55 56 57 58 59 19 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 20 of 22 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 9 Nakhai-Pour HR, Rey E, Berard A. Antihypertensive medication use during pregnancy and 5 6 the risk of major congenital malformations or small-for-gestational-age newborns. Birth 7 8 Defects Res B Dev Reprod Toxicol 2010 Apr;89(2):147-54. 9 10 11 12 10 Lydakis C, Lip GY, Beevers M et al. Atenolol and foetal growth in pregnancies complicated 13 14 by hypertension. Am J Hypertens 1999 Jun;12(6):541-7. 15 For peer review only 16 17 11 Abalos E, Duley L, Steyn DW et al. Antihypertensive drug therapy for mild to moderate 18 19 hypertension during pregnancy. Cochrane Database Syst Rev 2007;(1):CD002252. 20 21 22 23 12 Zeitlin J, El AM, Jarreau PH et al. Impact of foetal growth restriction on mortality and 24 25 morbidity in a very preterm birth cohort. J Pediatr 2010 Nov;157(5):733-9. 26 27 28 13 Challis JR, Lye SJ, Gibb W et al. Understanding preterm labor. Ann N Y Acad Sci 2001 29 30 Sep;943:225-34. 31 32

33 14 Knudsen LB. The Danish Fertility Database. Dan Med Bull 1998 Apr;45(2):221-5. http://bmjopen.bmj.com/ 34 35 36 37 15 Andersen TF, Madsen M, Jorgensen J et al. The Danish National Hospital Register. A 38 39 valuable source of data for modern health sciences. Dan Med Bull 1999 Jun;46(3):263-8. 40

41 on September 26, 2021 by guest. Protected copyright. 42 16 Gaist D, Sorensen HT, Hallas J. The Danish prescription registries. Dan Med Bull 1997 43 44 Sep;44(4):445-8. 45 46 47 17 Baadsgaard M, Quitzau J. Danish registers on personal income and transfer payments. 48 49 50 Scand J Public Health 2011 Jul;39(7 Suppl):103-5. 51 52 53 18 Jensen VM, Rasmussen AW. Danish education registers. Scand J Public Health 2011 54 55 Jul;39(7 Suppl):91-4. 56 57 58 59 20 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 21 of 22 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 19 Pedersen CB, Gotzsche H, Moller JO et al. The Danish Civil Registration System. A cohort 5 6 of eight million persons. Dan Med Bull 2006 Nov;53(4):441-9. 7 8 9 20 Knudsen LB, Borlum KF. Monitoring perinatal mortality and perinatal care with a national 10 11 12 register: content and usage of the Danish Medical Birth Register. Community Med 1986 13 14 Feb;8(1):29-36. 15 For peer review only 16 17 21 Karthikeyan VJ, Lip GY. Hypertension in pregnancy: pathophysiology and management 18 19 strategies. Curr Pharm Des 2007;13(25):2567-79. 20 21 22 23 22 Magee LA, Schick B, Donnenfeld AE et al. The safety of calcium channel blockers in 24 25 human pregnancy: a prospective, multicenter cohort study. Am J Obstet Gynecol 1996 26 27 Mar;174(3):823-8. 28 29 30 23 Podymow T, August P. Update on the use of antihypertensive drugs in pregnancy. 31 32 Hypertension 2008 Apr;51(4):960-9.

33 http://bmjopen.bmj.com/ 34 35 36 24 Lennestal R, Otterblad OP, Kallen B. Maternal use of antihypertensive drugs in early 37 38 pregnancy and delivery outcome, notably the presence of congenital heart defects in the 39 40 infants. Eur J Clin Pharmacol 2009 Jun;65(6):615-25.

41 on September 26, 2021 by guest. Protected copyright. 42 43 25 World Health Organization. Levels & Trends in Child Mortality. Report 2011. Estimates 44 45 Developed by the UN Inter-agency for Child Mortality Estimation. 2011. 46 47 48 http://www.who.int/child_adolescent_health/documents/child/childmortality_booklet_2011. 49 50 pdf, World Health Organization. 51 52 Ref Type: Online Source 53 54 55 56 57 58 59 21 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 22 of 22 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 26 Olesen C, Sondergaard C, Thrane N et al. Do pregnant women report use of dispensed 5 6 medications? Epidemiology 2001 Sep;12(5):497-501. 7 8

9 10 11 12 13 14 15 For peer review only 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

33 http://bmjopen.bmj.com/ 34 35 36 37 38 39 40

41 on September 26, 2021 by guest. Protected copyright. 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 22 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from

Beta-blocker treatment during pregnancy and adverse pregnancy outcomes: a nationwide population based cohort study

For peer review only Journal: BMJ Open

Manuscript ID: bmjopen-2012-001185.R1

Article Type: Research

Date Submitted by the Author: 26-Jun-2012

Complete List of Authors: Meidahl Petersen, Kasper; Rigshospitalet, University Hospital Copenhagen, Department of Clinical Pharmacology, Q Jimenez-Solem, Espen; Bispebjerg Hospital, Laboratory of Clinical Pharmacology Andersen, Jon Traerup; Bispebjerg Hospital, Department of Clinical Pharmacology Petersen, Morten; Bispebjerg Hospital, Department of Clinical Pharmacology Brødbæk, Kasper; Bispebjerg Hospital, Department of Clinical Pharmacology; Rigshospitalet, Laboratory of Clinical Pharmacology K�ber, Lars; Rigshospitalet, Department of Cardiology Torp-Pedersen, Christian; Gentofte Hospital, Department of Cardiology http://bmjopen.bmj.com/ Poulsen, Henrik; Bispebjerg Hospital, Department of Clinical Pharmacology; Rigshospitalet, Laboratory of Clinical Pharmacology

Primary Subject Pharmacology and therapeutics Heading:

Epidemiology, Evidence based practice, Reproductive medicine, obstetrics Secondary Subject Heading: and gynaecology

CLINICAL PHARMACOLOGY, Maternal medicine < OBSTETRICS, on September 26, 2021 by guest. Protected copyright. Keywords: EPIDEMIOLOGY

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 1 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 Beta-blocker treatment during pregnancy and adverse pregnancy outcomes: a nationwide 5 2 population-based cohort study 6 7 3 8 9 4 Kasper Meidahl Petersen MB1; Espen Jimenez-Solem MD1; Jon Trærup Andersen MD1; 10 11 5 Morten Petersen MD1, PhD; Kasper Brødbæk MD1; Lars Køber MD, DMSc2; Christian 12 13 6 Torp-Petersen MD, DMSc3; Henrik Enghusen Poulsen MD, DMSc1 14 15 For peer review only 16 7 17 18 8 Author affiliations 19 20 9 1: Department of Clinical Pharmacology, Q, Rigshospitalet, University Hospital Copenhagen, 21 22 10 Denmark 23 24 11 25 2: Department of Cardiology, Rigshospitalet, University Hospital Copenhagen, Denmark 26 27 12 3: Department of Cardiology, Gentofte Hospital, Gentofte, Denmark 28 29 13 30 31 14 Keywords (MeSH): Adrenergic beta-antagonists, pregnancy, small for gestational age infant, 32 15 premature birth, perinatal mortality. 33 http://bmjopen.bmj.com/ 34 35 16 Words: 3054 36 37 17 38 18 Correspondence to: 39 19 Kasper Meidahl Petersen 40 20 Department of Clinical Pharmacology, Q

41 21 Rigshospitalet, University Hospital Copenhagen on September 26, 2021 by guest. Protected copyright. 42 22 Tagensvej 20 43 23 DK-2200 Copenhagen N 44 24 Denmark 45 46 25 Tel +45 5123 7716 47 26 Fax +45 3545 2745 48 27 E-mail: [email protected] 49 28 50 51 29 52 53 30 54 55 31 56 57 58 59 1 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 2 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 5 6 2 ABSTRACT 7 8 3 Objective: To investigate the association between exposure to beta-blockers during pregnancy and 9 10 11 4 the risk of being born small for gestational age (SGA), preterm birth, and perinatal mortality in 12 13 5 a nationwide cohort. 14 15 6 Design: A population-basedFor peer retrospective cohortreview study, using the Danishonly Fertility Database. We 16 17 7 identified all pregnant women redeeming a prescription for beta-blockers using the National 18 19 20 8 Prescription Registry. Multivariate logistic regression models were used to assess the association 21 22 9 between exposure and our outcomes. 23 24 10 Setting: Register based survey. 25 26 11 Participants: 911685 births between 1995 and 2008 obtained from the Danish Fertility Database. 27 28 12 Outcome measures: Being born SGA was defined as having a birth weight below the tenth 29 30 th 31 13 percentile for the corresponding gestational week. Preterm birth was defined as birth before the 37 32

33 14 gestational week. Perinatal mortality was defined as either death occurring within the first 28 days http://bmjopen.bmj.com/ 34 35 15 of life, or stillbirth. Before 2004, foetal deaths were recorded as stillbirths if they occurred after 28 36 37 16 weeks of gestation, but since then stillbirth is recorded for deaths after 22 gestational weeks. 38 39 40 17 Results: We identified 2459 pregnancies exposed to beta-blockers. Beta-blocker exposure during

41 on September 26, 2021 by guest. Protected copyright. 42 18 pregnancy was found to be associated with increased risk of SGA; adjusted OR=1.97 (95% CI, 43 44 19 1.75–2.23), preterm birth; adjusted OR=2.26 (95% CI, 2.03–2.52) and perinatal mortality; adjusted 45 46 20 OR=1.89 (95 % CI, 1.25–2.84). Analyses were adjusted for socio-economic and maternal variables. 47 48 21 We found similar risk profiles for pregnancies exposed to labetalol and for pregnancies exposed to 49 50 51 22 other beta-blockers. 52 53 54 55 56 57 58 59 2 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 3 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 Conclusion: We found that exposure to beta-blockers during pregnancy was associated with being 5 6 2 born SGA, preterm birth and perinatal mortality. Our findings show that labetalol is not safer than 7 8 3 other beta-blockers during pregnancy.. 9 10 11 4 12 ARTICLE SUMMARY 13 14 5 Article focus 15 For peer review only 16 6 • There is contradictory evidence concerning the consequences of beta-blocker treatment 17 18 7 during pregnancy. 19 20 8 21 • This survey explores the effects of beta-blocker exposure during pregnancy in a Danish birth 22 23 9 cohort comprising all births in Denmark between 1995 and 2008. In addition we compared 24 25 10 risks associated with exposure to labetalol with exposure to other beta-blockers. 26 27 11 Key messages 28 29 12 30 • Redeeming prescriptions of beta-blockers was found to be significantly associated with 31 32 13 increased risk of being born SGA, preterm birth, and perinatal mortality.

33 http://bmjopen.bmj.com/ 34 14 • We found comparable risk profiles in labetalol-exposed pregnancies and in pregnancies 35 36 15 exposed to any other beta-blocker. 37 38 16 Strengths and limitations of this study 39 40 17 • This study is the largest of its kind to date, and covers an entire nation which minimises risk

41 on September 26, 2021 by guest. Protected copyright. 42 43 18 of selection bias. 44 45 19 • Given the study design, we were not able to adjust for treatment indication and severity of 46 47 20 maternal disease, nor were we able to rule out confounding by indication, the underlying 48 49 50 21 maternal disease, as a possible explanation for our findings. 51 52 22 53 54 55 23 INTRODUCTION 56 57 58 59 3 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 4 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 Beta-blockers are widely used in the treatment of chronic hypertension,[1-4] migraine,[5] essential 5 6 2 tremor[6], and various other conditions. There is contradictory evidence concerning the 7 8 3 consequences of beta-blocker treatment during pregnancy. Some studies report an association 9 10 11 4 between beta-blocker treatment and small for gestational age (SGA) newborns, and preterm 12 13 5 birth,[4,7-10] while others do not.[2,11] Preterm birth and being born SGA are both associated with 14 15 6 increased risk ofFor perinatal mortality.[12,13]peer reviewWe set out to investigate only whether the use of beta- 16 17 7 blockers during pregnancy was associated with being born SGA, preterm birth and perinatal 18 19 20 8 mortality in a nationwide survey between 1995 and 2008. 21 22 9 23 24 10 METHOD 25 26 11 Study population 27 28 12 We used data obtained from three nationwide registries: the Danish Fertility Database,[14] the 29 30 31 13 Danish National Hospital Register[15], and the National Prescription Register.[16] Data concerning 32

33 14 income and educational level were obtained respectively from the Income Statistics Register[17] http://bmjopen.bmj.com/ 34 35 15 and the Danish Education register,[18] both of which are provided by Statistics Denmark. In 36 37 16 Denmark all citizens are given a unique ten-digit identification number at birth.[19] This number 38 39 40 17 can be used to link information between nationwide registers.

41 on September 26, 2021 by guest. Protected copyright. 42 18 Using the Danish Fertility Database we identified 974 805 births between 1995 and 2008. We 43 44 19 removed 52 603 records lacking information on pregnancy duration and 7681 records with coding 45 46 20 errors. In addition, we excluded 2836 records with pregnancy-induced hypertension, defined as 47 48 21 having redeemed an antihypertensive drug prescription after the twentieth week of gestation, but 49 50 51 22 never before. The final study population thus comprised 911 685 births. 52 53 23 The Danish Fertility Database contains information on maternal age, date of birth, and 54 55 24 previous births, as well as on each child’s sex, gestational age, weight, and mortality.[14] 56 57 58 59 4 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 5 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 Time of conception is based on ultrasound estimates in early pregnancy, or information on last 5 6 2 menstrual period. 7 8 3 Information on redeemed prescriptions was retrieved from the National Prescription Register, 9 10 11 4 which holds information on date of redemption, quantity, strength, and form.[16] Drugs are coded 12 13 5 in accordance with the Anatomical Therapeutic Chemical (ATC) classification. 14 15 6 The DanishFor National Hospitalpeer Register review contains information onlyon diagnoses of somatic 16 17 7 admissions and outpatients at all Danish hospitals since 1977[15] in accordance with the Danish 18 19 20 8 revision of the 10th International Classification of Diseases (ICD)-system. We used primary 21 22 9 discharge diagnoses and disregarded secondary diagnoses, because secondary diagnoses in general 23 24 10 are not validated. We identified diagnoses of pre-eclampsia and eclampsia, migraine, essential 25 26 11 tremor, arrhythmias and maternal smoking. Pre-eclampsia and eclampsia were defined as women 27 28 12 diagnosed with O13, O14, or O15. Migraine was defined as G43 or G44, essential tremor as G250 29 30 31 13 and arrhythmias as I47, I48, and I49. Maternal smoking was defined as women diagnosed with 32

33 14 UT00, UT20, UT21, UT22, and UT23. http://bmjopen.bmj.com/ 34 35 15 36 37 38 16 Identification of Exposure 39 40 17 We defined exposure to beta-blockers as the redemption of at least two prescriptions between six

41 on September 26, 2021 by guest. Protected copyright. 42 18 months before conception and the twentieth week of gestation. At least one of these prescriptions 43 44 19 had to be redeemed between conception and the twentieth week of gestation. 45 46 20 47 We assessed exposure to beta-blockers by identifying redeemed prescriptions with ATC code C07. 48 49 21 Furthermore, we identified the most frequently redeemed beta-blockers in Denmark: labetalol 50 51 22 (C07AG01), metoprolol (C07AB02), atenolol (C07AB03), propranolol (C07AA05), pindolol 52 53 23 (C07AA03), and sotalol (C07AA07). Fewer than 50 pregnancies were exposed to any of the 54 55 24 remaining beta-blockers. 56 57 58 59 5 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 6 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 We divided beta-blocker exposure into exposure to labetalol and exposure to other beta- 5 6 2 blockers. The latter group was formed because there were few redeemed prescriptions of individual 7 8 3 beta-blockers other than labetalol. We compared risks associated with exposure to beta-blockers 9 10 11 4 with exposure to methyldopa (C02AB01, C02AB02), calcium channel blockers (C08C), and ACE 12 13 5 inhibitors (C09A) to assess possible confounding by indication. 14 15 6 Maternal diabetesFor mellitus peer was defined review as redeeming a prescription only for insulin or an insulin 16 17 7 analogue (ATC code A10A). Furthermore, we assessed co-medication with statins (ATC code C10) 18 19 20 8 and antiobesity drugs (ATC code A08A). We identified pregnant women redeeming prescriptions 21 22 9 with these drugs in order to adjust for diabetes mellitus, obesity, and statin use since these women 23 24 10 have different risk profiles for the defined outcomes. 25 26 11 27 28 29 12 Definition of Outcomes 30 31 13 Being born SGA was defined as having a birth weight below the tenth percentile for the 32

33 14 corresponding gestational week. Preterm birth was defined as birth before the 37th gestational week. http://bmjopen.bmj.com/ 34 35 15 Perinatal mortality was defined as either death occurring within the first 28 days of life, or stillbirth. 36 37 38 16 Before 2004, foetal deaths were recorded as stillbirths if they occurred after 28 weeks of gestation, 39 40 17 but since then stillbirth is recorded for deaths after 22 gestational weeks.[20]

41 on September 26, 2021 by guest. Protected copyright. 42 18 43 44 45 19 Statistical analyses 46 47 20 Data were managed and analysed using SAS 9.2 (SAS Institute Inc., Cary, NC, USA). Logistic 48 49 21 regression models were developed for dichotomous variables adjusted for maternal age, year of 50 51 22 conception, annual household income, parity, and educational level (model 1). Maternal age was 52 53 23 54 divided into five groups: <20, 21-25, 26-30, 31-35, >35 years (no missing values). Annual 55 56 24 household income at year of birth was divided into quartiles (1266 missing values). Subjects were 57 58 59 6 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 7 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 divided into quartiles according to the number of previous births, including stillbirths (37 missing 5 6 2 values): 0, 1, 2, ≥3 births. Year of conception was ordered into three categories (1994-1998, 1999- 7 8 3 2003, and 2004-2008). Educational level was divided into tertiles by highest level of education 9 10 11 4 achieved at the year of birth. For missing information we used information from the following 12 13 5 calendar year (32 745 missing values). 14 15 6 We constructedFor a separate peer logistic regression review model (model 2)only including the socio-economic 16 17 7 variables in model 1 and additional confounding variables: smoking status, co-medication (yes/no) 18 19 20 8 with statins, antiobesity drugs, insulin and insulin analogues, and diagnoses of pre- 21 22 9 eclampsia/eclampsia. These confounders were included in model 2 due to the high frequency of 23 24 10 missing data, because information on smoking and diagnoses of pre-eclampsia/eclampsia were not 25 26 11 available for the years 1995 and 2008. Maternal smoking was divided into four categories according 27 28 12 to the number of cigarettes smoked daily (0, 1-10, 11-20, >20). 29 30 31 13 When estimating the risk of perinatal mortality, analyses were further adjusted for previous 32

33 14 stillbirths. Odds ratios are presented with 95% confidence intervals (95% CIs). For description of http://bmjopen.bmj.com/ 34 35 15 basic characteristics we used frequencies with percentages. We used Chi-square tests to analyse 36 37 16 differences in the proportions of the different classes of categorical baseline characteristics. 38 39 40 17 Statistical significance was defined as p<0.05. All tests were two-sided.

41 on September 26, 2021 by guest. Protected copyright. 42 18 In addition, we carried out a propensity score-matched regression analysis to consolidate our 43 44 19 findings. We calculated a propensity score for the likelihood of redeeming a beta-blocker during 45 46 20 pregnancy by multivariate logistic regression conditional on baseline covariates. Using the Greedy 47 48 21 matching macro (http://mayoresearch.mayo.edu/mayo/research/biostat/upload/gmatch.sas), we 49 50 51 22 matched each case to four controls on the basis of the propensity score (table 1). We did not match 52 53 23 on diagnoses of pre-eclampsia/eclampsia since a large fraction of these cases redeemed beta-blocker 54 55 24 prescriptions. 56 57 58 59 7 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 8 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 5 6 7 2 RESULTS 8 9 10 3 Table 1 presents maternal characteristics in beta-blocker-exposed and unexposed women (number 11 12 4 and percentage of pregnancies). We identified 2381 pregnancies exposed to only one beta-blocker, 13 14 5 1452 exposed to labetalol only, and 929 exposed to other beta-blockers. 98 pregnancies were 15 For peer review only 16 17 6 exposed to more than one beta-blocker. We found 515 pregnancies exposed to methyldopa, 86 18 19 7 pregnancies to calcium channel blockers (CCBs), and 48 pregnancies exposed to ACE inhibitors. 20 21 8 Women exposed to beta-blockers during pregnancy were older, had higher income, and higher 22 23 9 parity than unexposed women. The proportions of women redeeming prescriptions for statins, 24 25 26 10 antiobesity preparations, and insulins were higher among the beta-blocker-exposed group. The 27 28 11 proportion of pregnancies complicated by pre-eclampsia was higher among beta-blocker-exposed 29 30 12 pregnancies. There was no difference in smoking prevalence between beta-blocker-exposed and 31 32 13 unexposed women (table 1).

33 http://bmjopen.bmj.com/ 34 35 14 36 37 15 38 39 16 40

41 on September 26, 2021 by guest. Protected copyright. 17 42 43 18 44 45 46 19 47 48 20 49 50 21 51 52 22 53 54 23 55 56 24 57 58 59 8 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 9 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 5 6 2 7 8 3 9 10 4 Beta-blocker-exposed Beta-blocker-unexposed Propensity matched 11 12 Table 1. Basic characteristics for pregnancies exposed to beta-blockers, compared with unexposed 13 pregnancies and propensity score-matched pregnancies. 14 15 For (n=2459) peer review (n=909228) only (n=9662) a a 16 Characteristics n (%) n (%) p-value n (%) p-value 17 Educational level <0.001 0.991 18 Low 739 (30.05) 311 600 (35.45) 2965 (30.69) 19 Medium 972 (39.53) 285 450 (32.47) 3883 (40.19) 20 High 707 (28.75) 279 431 (31.79) 2814 (29.12) 21 Annual household income (GBP) 22 <0.001 0.989 23 0- 36 770 509 (23.99) 226 228 (24.84) 1924 (19.91) 24 36 771 – 52 703 594 (24.16) 227 195 (24.96) 2337 (24.19) 25 52 704 – 74 699 662 (26.92) 227 089 (24.94) 2631 (27.23) 26 ≥ 74 700 693 (28.18) 227 448 (24.98) 2770 (28.67) 27 Parity <0.001 0.998 28 1 900 (36.60) 394 661 (43.29) 3487 (28.87) 29 30 2 918 (37.33) 338 989 (37.18) 3658 (30.28) 31 3 455 (18.50) 129 482 (14.20) 1788 (14.80) 32 >3 186 (7.56) 46 057 (5.05) 729 (6.04)

33 Age (years) <0.001 1.000 http://bmjopen.bmj.com/ 34 <20 18 (0.73) 26 321 (2.89) 68 (0.56) 35 21-25 174 (7.07) 147 298 (16.16) 699 (5.79) 36 26-30 700 (28.47) 350 105 (38.40) 2757 (22.82) 37 38 31-35 930 (37.82) 281 154 (30.84) 3665 (30.34) 39 >35 637 (24.90) 104 339 (11.44) 2473 (20.47) 40 Daily cigarettesb 0.427 0.385

41 0 1548 (80.29) 572 642 (81.15) 6140 (81.81) on September 26, 2021 by guest. Protected copyright. 42 1-10 251 (13.02) 90 033 (12.76) 913 (12.16) 43 11-20 114 (5.19) 36201 (5.13) 394 (5.25) 44 >20 15 (0.78) 4849 (0.69) 59 (0.79) 45 46 Statins <0.001 0.492 47 Used 5 (0.20) 111 (0.01) 14 (0.14) 48 Not used 2454 (99.8) 909 115 (99.99) 9648 (99.86) 49 Antiobesity preparations (A10) 0.018 0.251 50 51 Used 9 (0.40) 1539 (0.17) 23 (0.24) 52 Not used 2450 (99.6) 907 687 (99.83) 9639 (99.76)

53 Insulins and analogues <0.001 0.782 54 Used 101 (4.11) 4208 (0.46) 412 (4.14) 55 56 Not used 2358 (95.89) 905 018 (99.53) 9250 (95.74)

57 Pre-eclampsia diagnosis(O13-O15) <0.001 58 59 9 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 10 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 Yes 99 (4.03) 7806 (0.86) - 5 No 2360 (95.97) 901 420 (99.14) - 6 1 7 a 8 2 Chi-square tests were used to assess the overall p value for the group comparison. 9 10 bInformation on smoking was only available for 1996-2007. 11 3 12 13 14 4 Women redeeming labetalol prescriptions were older, had a higher education level, and a 15 For peer review only 16 5 higher prevalence of preeclampsia and smoking than women exposed to other beta-blockers (table 17 18 6 2). The proportion of women redeeming prescriptions for insulin was larger among the labetalol- 19 20 7 exposed group. There was no difference in income or co-medication with statins and antiobesity 21 22 8 23 preparations between the two groups. Diagnoses of migraine and arrhythmias were more common 24 25 9 among women exposed to any other beta-blocker. Women exposed to other beta-blockers had 26 27 10 higher parity than those exposed to labetalol. 28 29 Table 2. Basic characteristics for pregnancies exposed to labetalol, 30 11 31 compared with pregnancies exposed to other beta-blockers. 32

33 http://bmjopen.bmj.com/ 34 Labetalol Other beta-blockers 35 (n=1452) (n=929) 36 Characteristics n (%) n (%) p-valuea 37 Educational level <0.001 38 39 Low 391 (26.93) 321 (34.55) 40 Medium 571 (39.33) 369 (39.72)

41 High 462 (31.82) 226 (24.33) on September 26, 2021 by guest. Protected copyright. 42 43 Annual household income (GBP) 0.138 44 0 – 36 770 202 (13.91) 289 (31.11) 45 36 771 – 52 703 223 (15.36) 357 (38.43) 46 52 704 – 74 699 228 (15.70) 413 (44.46) 47 48 ≥74 700 275 (19.94) 393 (42.30) 49 Parity 0.004 50 0 512 (35.26) 363 (39.07) 51 1 586 (40.36) 308 (33.15) 52 53 2 256 (17.63) 179 (19.27) 54 ≥3 98 (6.75) 79 (8.50) 55 Age (years) <0.001 56 57 <20 7 (0.58) 10 (1.08) 58 59 10 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 11 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 21-25 69 (4.75) 97 (10.44) 5 26-30 406 (27.96) 275 (29.60) 6 7 31-35 586 (40.36) 314 (33.79) 8 >35 384 (26.45) 233 (25.08) 9 Daily cigarettesb <0.001 10 11 0 933 (64.26) 565 (60.82) 12 1-10 130 (8.95) 112 (12.06) 13 11-20 44 (3.03) 62 (6.67) 14 >20 9 (6.19) 6 (0.65) 15 For peer review only 16 Antiobesity drugs 0.052 17 Yes 5 (0.34) 9 (0.97) 18 No 1447 (99.66) 920 (99.03) 19 Statins 0.261 20 21 Yes 5 (0.34) 1 (0.10) 22 No 1447 (99.66) 928 (99.90) 23 Insulins and analogues <0.001 24 25 Yes 83 (5.72) 16 (1.72) 26 No 1369 (94.28) 913 (92.28) 27 Migraine <0.001 28 Yes 26 (1.79) 46 (4.95) 29 30 No 1426 (98.21) 883 (95.05) 31 Pre-eclampsia 32 diagnosis 0.001

33 Yes 74 (5.10) 21 (2.26) http://bmjopen.bmj.com/ 34 No 1378 (94.90) 908 (97.84) 35 Arrhythmia <0.001 36 37 Yes 23 (1.58) 82 (8.83) 38 No 1429 (98.42) 847 (91.17) 39 Essential tremor 0.030 40 Yes - 3 (0.33)

41 on September 26, 2021 by guest. Protected copyright. 42 No 1452 (100) 926 (99.67) 43 1 a 44 Chi square tests were used to assess the overall p value for the group 45 comparison. 46 2 47 bInformation on smoking was only available for 1996-2007. 48 3 49 50 51 4 Table 3 presents ORs with 95% CIs for SGA, preterm birth and perinatal death for exposure 52 53 5 to beta-blockers during pregnancy. 54 55 6 56 57 58 59 11 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 12 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 SGA 5 6 2 We found 93 662 children born SGA in the unexposed population (table 3). There were 446 7 8 3 children born SGA among pregnancies exposed to some kind of beta-blocker. We found a higher 9 10 11 4 proportion of SGA among women exposed to beta-blockers compared with unexposed women. 12 13 5 Women exposed to labetalol or to other beta-blockers had similarly higher odds ratios than 14 15 6 unexposed womenFor (table 3). peer review only 16 17 7 18 19 20 8 Preterm birth 21 22 9 We identified 109 163 preterm births in the unexposed population (table 3). There were 697 preterm 23 24 10 births among pregnancies exposed to beta-blockers. We found an association between preterm birth 25 26 11 27 and beta-blocker exposure compared with unexposed women. Those exposed to labetalol or to other 28 29 12 beta-blockers had similarly higher odds ratios than unexposed women (table 3). 30 31 13 32

33 http://bmjopen.bmj.com/ 14 34 Perinatal mortality 35 36 15 We identified 6048 perinatal deaths in the unexposed population (table 3). There were 44 perinatal 37 38 16 deaths among infants exposed to beta-blockers. We found a higher rate of perinatal mortality 39 40 17 amongst women exposed to beta-blockers (table 3).

41 on September 26, 2021 by guest. Protected copyright. 42 18 When stratifying for different beta-blockers we found 30 perinatal deaths among labetalol- 43 44 45 19 exposed pregnancies. Labetalol exposure was associated with increased risk of perinatal mortality 46 47 20 (table 3). 48 49 21 We identified 13 perinatal deaths among pregnancies exposed to other beta-blockers. 50 51 22 Exposure to other beta-blockers was found to be significantly associated with perinatal mortality in 52 53 23 54 the unadjusted model and model 1. However, adjusting our analysis for additional confounding 55 56 24 variables (Model 2) rendered the association statistically insignificant (table 3). 57 58 59 12 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 13 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 5 6 2 7 Other analyses 8 9 3 We identified 515 pregnancies exposed to methyldopa (table 3). We found 61 children born SGA, 10 11 4 216 preterm births and 4 perinatal deaths among these pregnancies. We found a positive association 12 13 5 between children born SGA and exposure to methyldopa, and between methyldopa exposure and 14 15 6 increased risk ofFor preterm birth. peer Exposure to reviewmethyldopa during pregnancy only was not significantly 16 17 18 7 associated with perinatal mortality (table 3). 19 20 8 21 22 9 Table 3. ORs with 95% CIs for SGA, preterm birth and perinatal death for exposure to beta- 23 24 25 10 blockers during pregnancy. 26 27 11 28 29 30 31 32

33 http://bmjopen.bmj.com/ 34 35 36 37 38 39 40

41 on September 26, 2021 by guest. Protected copyright. 42 43 44 45 46 47 48 49 50 51 52 53 Table 3 Odds Ratios (ORs) with 95% CI for SGA, preterm birth and perinatal death for exposure to beta-blockers 54 during pregnancy. 55 56 57 58 59 13 60

Analyses are adjustedFor peer for maternalreview only age, household- http://bmjopen.bmj.com/site/about/guidelines.xhtml income, educational level, parity, birth year and prior stillbirths. aModel 2 is furthermore adjusted for smoking and comedication with statins, antiobesity preparations, insulins and diagnoses of pre-eclampsia/eclampsia. The cohort in model 2 comprises all births between 1996 and 2007 (n=778 394). BMJ Open Page 14 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 Exposure Crude Adjusted (model 1) Adjusted (model 2) 4 N (%) OR (95% CI) OR (95% CI) OR (95% CI) 5 SGA 6 7 Unexposed (n=909 226) 93 662 (10.30) Reference Reference Reference 8 All beta-blockers (n=2459) 446 (18.14) 1.93 (1.74-2.14) 1.99 (1.79-2.21) 1.97 (1.75-2.23) 9 Labetalol only (n=1452) 258 (17.77) 1.88 (1.64-2.15) 1.95 (1.70-2.24) 2.02 (1.72-2.37) 10 11 Other beta-blockers (n=929) 179 (19.27) 2.08 (1.76-2.44) 2.11 (1.79-2.49) 2.01 (1.66-2.43) 12 Methyldopa (n= 515) 61 (11.84) 1.17 (0.89-1.53) 1.32 (1.01-1.73) 1.43 (1.04-1.96) 13 CCBs (n=86) 21 (24.42) 2.30 (1.42-3.73) 2.24 (1.36-3.67) 1.88 (1.02-3.49) 14

15 For peer review only 16 Preterm birth 17 Unexposed (n=909 226) 109 163 (12.01) Reference Reference Reference 18 All beta-blockers (n=2459) 697 (28.34) 2.9 (2.66-3.14) 2.71 (2.48-2.97) 2.26 (2.03-2.52) 19 20 Labetalol only (n=1452) 473 (32.58) 3.54 (3.17-3.95) 3.33 (2.98-3.72) 2.74 (2.39-3.13) 21 Other beta-blockers (n=929) 206 (22.17) 2.08 (1.78-2.43) 1.93 (1.65-2.26) 1.69 (1.41-2.03) 22 Methyldopa (n= 515) 216 (41.94) 5.29 (4.44-6.31) 5.03 (4.21-6.01) 4.21 (3.38-5.23) 23 CCBs (n=86) 26 (30.23) 2.55 (1.63-3.99) 2.50 (1.60-3.89) 2.15 (1.26-3.67) 24 25 26 Perinatal mortality 27 Unexposed (n=909 226) 6048 (0.67) Reference Reference Reference 28 29 All beta-blockers (n=2459) 44 (1.79) 2.72 (2.02-3.67) 2.69 (1.98-3.65) 1.89 (1.25-2.84) 30 Labetalol only (n=1452) 30 (2.07) 3.15 (2.19-4.52) 3.24 (2.25-4.67) 2.08 (1.26-3.44) 31 Other beta-blockers (n=929) 13 (1.39) 2.12 (1.22-3.66) 1.92 (1.08-3.40) 1.72 (0.85-3.48) 32 Methyldopa (n= 515) 4 (0.78) 1.15 (0.43-3.07) 1.16 (0.43-3.12) 0.35 (0.05-2.50)

33 http://bmjopen.bmj.com/ 34 CCBs (n=86) 1 (1.16) 1.78 (0.25-12.57) 2.00 (0.28-14.83) 3.26 (0.45-23.77) 35 1 36 37 2 38 39 3 40 4 41 We found 86 pregnancies exposed to calcium channel blockers (table 3). These included 17 on September 26, 2021 by guest. Protected copyright. 42 43 5 children born SGA, 18 preterm births and 1 perinatal death. We found an association between 44 45 6 exposure to calcium channel blockers and children born SGA in all models. 46 47 48 7 Additionally, we found an association between exposure to calcium channel blockers and 49 50 8 increased risk of preterm birth in all models. As with methyldopa, exposure to calcium channel 51 52 9 blockers during pregnancy was not found to be associated with perinatal mortality (table 3). 53 54 10 Analyses for exposure to ACE inhibitors were not performed since we identified only 48 55 56 11 57 pregnancies exposed to them. 58 59 14 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 15 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 Post hoc we analysed the effect of exposure to all beta-blockers using a propensity score- 5 6 2 matched control group (Table 1) and found similar results to those of the primary analyses: SGA, 7 8 3 OR=1.93 (95% CI, 1.71–2.19); preterm birth, OR=2.40 (95% CI, 2.16–2.67); perinatal mortality, 9 10 11 4 OR=3.22 (95% CI, 2.15–4.82). 12 13 5 14 15 6 DISCUSSION For peer review only 16 17 7 In the present study, which we believe to be the largest of its kind to date, we found an association 18 19 8 20 between redeeming prescriptions of beta-blockers during pregnancy and being born SGA, preterm 21 22 9 birth, and perinatal mortality. In addition, we found an association between redeeming prescriptions 23 24 10 of methyldopa and calcium channel blockers, being born SGA, and preterm birth. Methyldopa and 25 26 11 calcium channel blockers were not found to be associated with perinatal mortality. 27 28 12 We found exposure to any beta-blocker to be associated with being born SGA. Our results are 29 30 31 13 in accordance with a recent study reporting increased risk of being born SGA among pregnancies 32

33 14 exposed to selective beta-blockers (OR=6.00; 95% CI, 1.06–33.87) and labetalol (OR=2.26; 95% http://bmjopen.bmj.com/ 34 35 15 CI, 1.04–4.88).[9] Labetalol is generally considered safe for use during pregnancy.[1,8,21] 36 37 16 38 39 40 17 Exposure to beta-blockers was found to be associated with preterm birth. When stratifying for

41 on September 26, 2021 by guest. Protected copyright. 42 18 different beta-blockers we found an increased risk of preterm birth after exposure to labetalol, and 43 44 19 all other beta-blockers, respectively. 45 46 20 47 We found an association between exposure to beta-blockers and perinatal mortality. When 48 49 21 stratifying for different beta-blockers we found this association to be statistically significant for 50 51 22 exposure to labetalol and other beta-blockers. When adjusting our analysis for maternal co- 52 53 23 morbidity, co-medication, and smoking, only labetalol was found to be associated with perinatal 54 55 24 mortality. 56 57 58 59 15 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 16 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 Methyldopa is mainly used to treat chronic hypertension during pregnancy as first-line 5 6 2 therapy.[1] Previous studies did not find any associations between methyldopa exposure and being 7 8 3 born SGA or preterm birth.[1,3] Methyldopa has not been found to have effects on placental 9 10 11 4 haemodynamics.[1] However, a recent case-control study reported an increased risk of being born 12 13 5 SGA among pregnancies exposed to centrally acting adrenergic agents during the second and third 14 15 6 trimesters[9]: OR=1.70For (95% peer CI, 1.00–2.89). review We found that methyldopa only exposure was associated 16 17 7 with being born SGA and preterm birth. This could be due to indicative antihypertensive treatment 18 19 20 8 with methyldopa in pregnant women with diabetes or pregnancy related diabetes. The prevalence of 21 22 9 diabetes among methyldopa-exposed pregnancies was found to be higher: 11.1% compared with 23 24 10 3.9% among beta-blocker-exposed pregnancies. Increased risk of preterm birth was still seen after 25 26 11 adjusting our analyses for additional confounding variables in model 2. We found no association 27 28 12 between exposure to methyldopa and perinatal mortality. These findings are consistent with those of 29 30 31 13 a previous study.[3] 32

33 14 Calcium channel blockers are considered to be safe during pregnancy.[3,22] We found that http://bmjopen.bmj.com/ 34 35 15 exposure to calcium channel blockers was associated with being born SGA and with preterm birth. 36 37 16 The risk of being born SGA and preterm of birth remained after adjusting our analyses for 38 39 40 17 additional confounding variables in model 2. We found no statistically significant association

41 on September 26, 2021 by guest. Protected copyright. 42 18 between calcium channel blocker exposure during pregnancy and perinatal mortality. 43 44 19 We chose to analyse two outcomes previously reported to be associated with beta-blocker 45 46 20 exposure during pregnancy —SGA and preterm birth[1,10,23] — that have been associated with 47 48 21 increased perinatal mortality in previous studies.[12,13] Therefore we investigated the risk of 49 50 51 22 perinatal mortality among beta-blocker-exposed pregnancies. We compared risks associated with 52 53 23 exposure to beta-blockers with exposure to methyldopa and calcium channel blockers to assess 54 55 24 possible confounding by indication. Our analyses show a similar risk of being born SGA and an 56 57 58 59 16 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 17 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 increased risk of preterm birth for all recommended agents during pregnancy. There are various 5 6 2 possible explanations for this finding. It is possible that the underlying indication for treatment, 7 8 3 maternal disease, is the true risk factor. Possible maternal diseases include hypertension, either 9 10 11 4 predating or complicating pregnancy. Accordingly, we were not able to rule out a potential effect of 12 13 5 maternal disease on perinatal outcomes. 14 15 6 We foundFor an association peer between exposure review to beta-blockers onlyduring pregnancy and perinatal 16 17 7 mortality. This association was not found for exposure to methyldopa and calcium channel 18 19 20 8 blockers, which might be due to the small number of cases. 21 22 9 We believe that the similar risks found for exposure to the various beta-blockers and SGA, 23 24 10 preterm birth, and perinatal mortality are a class effect. This seems to be true in spite of statistically 25 26 11 significant differences in the basic characteristics of women exposed to labetalol and those exposed 27 28 12 to other beta-blockers (table 2). After adjustments were made for these variables, we found 29 30 31 13 comparable risk profiles for labetalol-exposed pregnancies and pregnancies exposed to other beta- 32

33 14 blockers. Most beta-blockers are known to cross the placenta,[21,24] and effects on placental http://bmjopen.bmj.com/ 34 35 15 haemodynamics have been observed in both human and animal studies. A mechanism has been 36 37 16 proposed of diminished placental blood flow due to the selective vasoconstriction of placental 38 39 40 17 vessels by beta-blockers without intrinsic sympathomimetic activity.[24] This effect on placental

41 on September 26, 2021 by guest. Protected copyright. 42 18 haemodynamics could explain growth retardation of foetuses exposed to beta-blockers during 43 44 19 pregnancy and might result in children being born SGA and preterm. 45 46 20 We defined exposure as redemption of at least two prescriptions between six months before 47 48 21 conception and the twentieth week of gestation. At least one of these prescriptions had to be 49 50 51 22 redeemed between conception and twentieth week of gestation. We believe that this model 52 53 23 increases the probability of identifying continuous use that extends into pregnancy. 54 55 56 57 58 59 17 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 18 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 The rate of perinatal mortality in Denmark is low (table 3).[25] A large number of women 5 6 2 exposed to beta-blockers, methyldopa, and calcium channel blockers are therefore needed to 7 8 3 identify a possible risk increase associated with these outcomes. Our cohort comprises all births in 9 10 11 4 Denmark between 1995 and 2008. This minimises confounding due to race, educational level, and 12 13 5 other socio-economic factors. The national Danish registers cover the entire nation and are 14 15 6 considered valid.For As part of peerthe national health review care reimbursement only scheme, Danish pharmacies are 16 17 7 required by law to register all redeemed prescriptions. Approximately 97.5% of all redeemed 18 19 20 8 prescriptions are registered in the Danish Prescription register.[16] Our study includes data on 21 22 9 exposure to beta-blockers based on information on prescriptions paid for at the pharmacy, and not 23 24 10 only prescribed by the physician, thereby increasing the probability of exposure. Furthermore, our 25 26 11 study was not confounded by recall bias since information was recorded prospectively. The Danish 27 28 12 Fertility Database contains more than 99% of all births during the study period.[14] 29 30 31 13 Limitations of our study include missing information on maternal weight and alcohol 32

33 14 consumption. We were unable to adjust for treatment indication and severity of maternal disease. http://bmjopen.bmj.com/ 34 35 15 Given the study design, we were not able to address this issue further, nor were we able to rule out 36 37 16 confounding by indication, the underlying maternal disease, as a possible explanation for our 38 39 40 17 findings. Consequently we were unable to differentiate between a possible class effect of beta-

41 on September 26, 2021 by guest. Protected copyright. 42 18 blockers and the effect of the underlying maternal disease. 43 44 19 Unfortunately information on diagnoses of essential hypertension was not available, since 45 46 20 these are known risk factors for our primary outcomes. 47 48 21 The prevalence of pre-eclampsia and eclampsia in the cohort is based on primary discharge 49 50 51 22 diagnoses from hospital admissions. We did not use secondary diagnoses, since these in general are 52 53 23 not validated. We estimated exposure from National Prescription Registry data, which contains 54 55 24 information on all redeemed prescriptions.[16] Overestimation of exposure is therefore a 56 57 58 59 18 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 19 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 possibility, since we cannot adjust for a potential lack of compliance. However, in a study by 5 6 2 Olesen et al. conducted in a cohort of pregnant Danish women in the county of North Jutland,[26] 7 8 3 compliance with prescribed beta-blockers was estimated to be complete, strengthening the validity 9 10 11 4 of our analyses. Furthermore, overestimation of exposure would bias the estimates towards unity. 12 13 5 There is a general consensus that labetalol is safer than other beta-blockers during pregnancy 14 15 6 and this drug is Forrapidly becoming peer the first-line review choice in conditions only such as chronic hypertension 16 17 7 during pregnancy.[21,23] We found an association between redeeming prescriptions for beta- 18 19 20 8 blockers and being born SGA, preterm birth, and perinatal mortality. Risk profiles for pregnancies 21 22 9 exposed to labetalol and to other beta-blockers were similar. The increasing use and uncertainty of 23 24 10 effects and possible side effects of treatment with beta-blockers during pregnancy call for further 25 26 11 studies to validate our findings. 27 28 12 29 30 31 13 Conflicts of interests 32

33 14 The authors have no relevant conflict of interests. http://bmjopen.bmj.com/ 34 35 15 36 37 16 Funding 38 39 17 The project was sponsored by the Capital Region of Copenhagen. 40

41 18 on September 26, 2021 by guest. Protected copyright. 42 43 19 44 Contributorship Statement 45 20 46 21 KMP, EJS, JTA, MP, KB, LK, CTP, HEP 47 22 48 23 KMP, EJS, JTA and HEP conceptualized the study. MP, KB, LK and CTP assisted with the study design. KMP 49 50 24 preformed the analyses assisted by EJS and JTA, MP, KB, LK, CTP and HEP assisted in the interpretation. 51 25 KMP, EJS, JTA, MP, KB, LK, CTP and HEP wrote and revised the final manuscript. Figure design was done by 52 26 KMP, EJS, JTA, MP, KB, LK, CTP and HEP. All authors approved the final version to be published. 53 54 27 55 56 28 57 58 59 19 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 20 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 REFERENCES 5 6 7 2 1 Sibai BM. Treatment of hypertension in pregnant women. N Engl J Med 1996 Jul 8 9 3 25;335(4):257-65. 10 11 12 4 2 Magee LA, Ornstein MP, von DP. Fortnightly review: management of hypertension in 13 14 15 5 pregnancy.For BMJ 1999 peer May 15;318(7194):1332-6. review only 16 17 18 6 3 Afifi Y, Churchill D. Pharmacological treatment of hypertension in pregnancy. Curr Pharm 19 20 7 Des 2003;9(21):1745-53. 21 22 23 8 4 Magee LA, Duley L. Oral beta-blockers for mild to moderate hypertension during 24 25 9 26 pregnancy. Cochrane Database Syst Rev 2003;(3):CD002863. 27 28 29 10 5 Modi S FAU - Lowder D, Lowder DM. Medications for migraine prophylaxis.(0002-838X 30 31 11 (Print)). 32

33 http://bmjopen.bmj.com/ 34 12 6 Lyons KE FAU - Pahwa R, Pahwa R. Pharmacotherapy of essential tremor : an overview of 35 36 13 existing and upcoming agents.(1172-7047 (Print)). 37 38 39 14 40 7 Sibai BM, Gonzalez AR, Mabie WC et al. comparison of labetalol plus hospitalization

41 on September 26, 2021 by guest. Protected copyright. 42 15 versus hospitalization alone in the management of preeclampsia remote from term. Obstet 43 44 16 Gynecol 1987 Sep;70(3 Pt 1):323-7. 45 46 47 17 8 Magee LA, Elran E, Bull SB et al. Risks and benefits of beta-receptor blockers for 48 49 18 pregnancy hypertension: overview of the randomized trials. Eur J Obstet Gynecol Reprod 50 51 52 19 Biol 2000 Jan;88(1):15-26. 53 54 55 56 57 58 59 20 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 21 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 9 Nakhai-Pour HR, Rey E, Berard A. Antihypertensive medication use during pregnancy and 5 6 2 the risk of major congenital malformations or small-for-gestational-age newborns. Birth 7 8 3 Defects Res B Dev Reprod Toxicol 2010 Apr;89(2):147-54. 9 10 11 12 4 10 Lydakis C, Lip GY, Beevers M et al. Atenolol and foetal growth in pregnancies complicated 13 14 5 by hypertension. Am J Hypertens 1999 Jun;12(6):541-7. 15 For peer review only 16 17 6 11 Abalos E, Duley L, Steyn DW et al. Antihypertensive drug therapy for mild to moderate 18 19 7 hypertension during pregnancy. Cochrane Database Syst Rev 2007;(1):CD002252. 20 21 22 8 23 12 Zeitlin J, El AM, Jarreau PH et al. Impact of foetal growth restriction on mortality and 24 25 9 morbidity in a very preterm birth cohort. J Pediatr 2010 Nov;157(5):733-9. 26 27 28 10 13 Challis JR, Lye SJ, Gibb W et al. Understanding preterm labor. Ann N Y Acad Sci 2001 29 30 11 Sep;943:225-34. 31 32

33 12 14 Knudsen LB. The Danish Fertility Database. Dan Med Bull 1998 Apr;45(2):221-5. http://bmjopen.bmj.com/ 34 35 36 13 37 15 Andersen TF, Madsen M, Jorgensen J et al. The Danish National Hospital Register. A 38 39 14 valuable source of data for modern health sciences. Dan Med Bull 1999 Jun;46(3):263-8. 40

41 on September 26, 2021 by guest. Protected copyright. 42 15 16 Gaist D, Sorensen HT, Hallas J. The Danish prescription registries. Dan Med Bull 1997 43 44 16 Sep;44(4):445-8. 45 46 47 17 17 Baadsgaard M, Quitzau J. Danish registers on personal income and transfer payments. 48 49 50 18 Scand J Public Health 2011 Jul;39(7 Suppl):103-5. 51 52 53 19 18 Jensen VM, Rasmussen AW. Danish education registers. Scand J Public Health 2011 54 55 20 Jul;39(7 Suppl):91-4. 56 57 58 59 21 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 22 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 19 Pedersen CB, Gotzsche H, Moller JO et al. The Danish Civil Registration System. A cohort 5 6 2 of eight million persons. Dan Med Bull 2006 Nov;53(4):441-9. 7 8 9 3 20 Knudsen LB, Borlum KF. Monitoring perinatal mortality and perinatal care with a national 10 11 12 4 register: content and usage of the Danish Medical Birth Register. Community Med 1986 13 14 5 Feb;8(1):29-36. 15 For peer review only 16 17 6 21 Karthikeyan VJ, Lip GY. Hypertension in pregnancy: pathophysiology and management 18 19 7 strategies. Curr Pharm Des 2007;13(25):2567-79. 20 21 22 8 23 22 Magee LA, Schick B, Donnenfeld AE et al. The safety of calcium channel blockers in 24 25 9 human pregnancy: a prospective, multicenter cohort study. Am J Obstet Gynecol 1996 26 27 10 Mar;174(3):823-8. 28 29 30 11 23 Podymow T, August P. Update on the use of antihypertensive drugs in pregnancy. 31 32 12 Hypertension 2008 Apr;51(4):960-9.

33 http://bmjopen.bmj.com/ 34 35 36 13 24 Lennestal R, Otterblad OP, Kallen B. Maternal use of antihypertensive drugs in early 37 38 14 pregnancy and delivery outcome, notably the presence of congenital heart defects in the 39 40 15 infants. Eur J Clin Pharmacol 2009 Jun;65(6):615-25.

41 on September 26, 2021 by guest. Protected copyright. 42 43 16 25 World Health Organization. Levels & Trends in Child Mortality. Report 2011. Estimates 44 45 17 Developed by the UN Inter-agency for Child Mortality Estimation. 2011. 46 47 48 18 http://www.who.int/child_adolescent_health/documents/child/childmortality_booklet_2011. 49 50 19 pdf, World Health Organization. 51 52 20 Ref Type: Online Source 53 54 55 56 57 58 59 22 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 23 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 26 Olesen C, Sondergaard C, Thrane N et al. Do pregnant women report use of dispensed 5 6 2 medications? Epidemiology 2001 Sep;12(5):497-501. 7 8 3 9 10 11 4 12 13 14 15 For peer review only 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

33 http://bmjopen.bmj.com/ 34 35 36 37 38 39 40

41 on September 26, 2021 by guest. Protected copyright. 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 23 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 24 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 Beta-blocker treatment during pregnancy and adverse pregnancy outcomes: a nationwide 5 2 population-based cohort study 6 7 3 8 9 4 Kasper Meidahl Petersen MB1; Espen Jimenez-Solem MD1; Jon Trærup Andersen MD1; 10 11 5 Morten Petersen MD1, PhD; Kasper Brødbæk MD1; Henrik Enghusen Poulsen MD, DMSc1; 12 13 6 Lars Køber MD, DMSc2; Christian Torp-Petersen MD, DMSc3; Henrik Enghusen Poulsen 14 15 1 For peer review only 16 7 MD, DMSc 17 18 8 19 20 9 Author affiliations 21 22 10 1: Department of Clinical Pharmacology, Q, Rigshospitalet, University Hospital Copenhagen, 23 24 11 25 Denmark 26 27 12 2: Department of Cardiology, Rigshospitalet, University Hospital Copenhagen, Denmark 28 29 13 3: Department of Cardiology, Gentofte Hospital, Gentofte, Denmark 30 31 14 32

33 http://bmjopen.bmj.com/ 15 Keywords (MeSH): Adrenergic betaantagonists, pregnancy, small for gestational age infant, 34 35 16 premature birth, perinatal mortality. 36 37 17 Words: 2995 3054 38 39 18 40 19 Correspondence to:

41 20 Kasper Meidahl Petersen on September 26, 2021 by guest. Protected copyright. 42 21 Department of Clinical Pharmacology, Q 43 22 Rigshospitalet, University Hospital Copenhagen 44 23 Tagensvej 20 45 46 24 DK2200 Copenhagen N 47 25 Denmark 48 26 Tel +45 5123 7716 49 27 Fax +45 3545 2745 50 28 Email: [email protected] 51 29 52 53 30 54 55 31 56 57 58 59 1 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 25 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 5 6 2 7 8 3 9 ABSTRACT 10 11 4 Objective: To investigate the association between exposure to betablockers during pregnancy and 12 13 5 the risk of being born small for gestational age (SGA), preterm birth, and perinatal mortality in 14 15 6 a nationwide cohort.For peer review only 16 17 7 Design: A populationbased retrospective cohort study, using the Danish Fertility Database. We 18 19 20 8 identified all pregnant women redeeming a prescription for betablockers using the National 21 22 9 Prescription Registry. Multivariate logistic regression models were used to assess the association 23 24 10 between exposure and our outcomes. 25 26 11 Setting: Register based survey. 27 28 12 Participants: 911685 births between 1995 and 2008 obtained from the Danish Fertility Database. 29 30 31 13 Outcome measures: Being born SGA was defined as having a birth weight below the tenth 32 th 33 14 percentile for the corresponding gestational week. Preterm birth was defined as birth before the 37 http://bmjopen.bmj.com/ 34 35 15 gestational week. Perinatal mortality was defined as either death occurring within the first 28 days 36 37 16 of life, or stillbirth. Before 2004, foetal deaths were recorded as stillbirths if they occurred after 28 38 39 40 17 weeks of gestation, but since then stillbirth is recorded for deaths after 22 gestational weeks.

41 on September 26, 2021 by guest. Protected copyright. 42 18 Results: We identified 2459 pregnancies exposed to betablockers. Betablocker exposure during 43 44 19 pregnancy was found to be associated with increased risk of SGA; adjusted OR=1.97 (95% CI, 45 46 20 1.75–2.23), preterm birth; adjusted OR=2.26 (95% CI, 2.03–2.52) and perinatal mortality; adjusted 47 48 21 OR=1.89 (95 % CI, 1.25–2.84). Analyses were adjusted for socioeconomic and maternal variables. 49 50 51 22 We found similar risk profiles for pregnancies exposed to labetalol and for pregnancies exposed to 52 53 23 other betablockers. 54 55 56 57 58 59 2 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 26 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 Conclusion: We found that exposure to betablockers during pregnancy was associated with being 5 6 2 born SGA, preterm birth and perinatal mortality. Our findings show that labetalol is not safer than 7 8 3 other betablockers during pregnancy., and future treatment of pregnant women with betablockers 9 10 11 4 should therefore be based primarily on the individual needs of the mother and not the unborn child. 12 13 14 5 ARTICLE SUMMARY 15 For peer review only 16 6 Article focus 17 18 7 • There is contradictory evidence concerning the consequences of betablocker treatment 19 20 8 during pregnancy. 21 22 23 9 • This survey explores the effects of betablocker exposure during pregnancy in a Danish birth 24 25 10 cohort comprising all births in Denmark between 1995 and 2008. In addition we compared 26 27 11 risks associated with exposure to labetalol with exposure to other betablockers. 28 29 12 Key messages 30 31 32 13 • Redeeming prescriptions of betablockers was found to be significantly associated with

33 http://bmjopen.bmj.com/ 34 14 increased risk of being born SGA, preterm birth, and perinatal mortality. 35 36 15 • We found comparable risk profiles in labetalolexposed pregnancies and in pregnancies 37 38 16 exposed to any other betablocker. 39 40 17 Strengths and limitations of this study

41 on September 26, 2021 by guest. Protected copyright. 42 43 18 • This study is the largest of its kind to date, and covers an entire nation which minimises risk 44 45 19 of selection bias. 46 47 20 48 • Given the study design, we were not able to adjust for treatment indication and severity of 49 50 21 maternal disease, nor were we able to rule out confounding by indication, the underlying 51 52 22 maternal disease, as a possible explanation for our findings. 53 54 23 55 56 57 58 59 3 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 27 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 INTRODUCTION 5 6 2 Betablockers are widely used in the treatment of chronic hypertension,[14] migraine,[5] essential 7 8 3 tremor[6], and various other conditions. There is contradictory evidence concerning the 9 10 11 4 consequences of betablocker treatment during pregnancy. Some studies report an association 12 13 5 between betablocker treatment and small for gestational age (SGA) newborns, and preterm 14 15 6 birth,[4,710] whileFor others dopeer not.[2,11] Preterm review birth and being bornonly SGA are both associated with 16 17 7 increased risk of perinatal mortality.[12,13] We set out to investigate whether the use of beta 18 19 20 8 blockers during pregnancy was associated with being born SGA, preterm birth and perinatal 21 22 9 mortality in a nationwide survey between 1995 and 2008. 23 24 10 25 26 11 METHOD 27 28 12 29 Study population 30 31 13 We used data obtained from three nationwide registries: the Danish Fertility Database,[14] the 32

33 14 Danish National Hospital Register[15], and the National Prescription Register.[16] Data concerning http://bmjopen.bmj.com/ 34 35 15 income and educational level were obtained respectively from the Income Statistics Register[17] 36 37 16 and the Danish Education register,[18] both of which are provided by Statistics Denmark. In 38 39 40 17 Denmark all citizens are given a unique tendigit identification number at birth.[19] This number

41 on September 26, 2021 by guest. Protected copyright. 42 18 can be used to link information between nationwide registers. 43 44 19 Using the Danish Fertility Database we identified 974 805 births between 1995 and 2008. We 45 46 20 removed 52 603 records lacking information on pregnancy duration and 7681 records with coding 47 48 21 errors. In addition, we excluded 2836 records with pregnancyinduced hypertension, defined as 49 50 51 22 having redeemed an antihypertensive drug prescription after the twentieth week of gestation, but 52 53 23 never before. The final study population thus comprised 911 685 births. 54 55 56 57 58 59 4 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 28 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 The Danish Fertility Database contains information on maternal age, date of birth, and 5 6 2 previous births, as well as on each child’s sex, gestational age, weight, and mortality.[14] 7 8 3 Time of conception is based on ultrasound estimates in early pregnancy, or information on last 9 10 11 4 menstrual period. 12 13 5 Information on redeemed prescriptions was retrieved from the National Prescription Register, 14 15 6 which holds informationFor on peerdate of redemption, review quantity, strength, only and form.[16] Drugs are coded 16 17 7 in accordance with the Anatomical Therapeutic Chemical (ATC) classification. 18 19 20 8 The Danish National Hospital Register contains information on diagnoses of somatic 21 22 9 admissions and outpatients at all Danish hospitals since 1977[15] in accordance with the Danish 23 24 10 revision of the 10th International Classification of Diseases (ICD)system. We used primary 25 26 11 discharge diagnoses and disregarded secondary diagnoses, because secondary diagnoses in general 27 28 12 are not validated. We identified diagnoses of preeclampsia and eclampsia, migraine, essential 29 30 31 13 tremor, arrhythmias and maternal smoking. Preeclampsia and eclampsia were defined as women 32

33 14 diagnosed with O13, O14, or O15. Migraine was defined as G43 or G44, essential tremor as G250 http://bmjopen.bmj.com/ 34 35 15 and arrhythmias as I47, I48, and I49. Maternal smoking was defined as women diagnosed with 36 37 16 UT00, UT20, UT21, UT22, and UT23. 38 39 40 17

41 on September 26, 2021 by guest. Protected copyright. 42 18 Identification of Exposure 43 44 19 We defined exposure to betablockers as the redemption of at least two prescriptions between six 45 46 20 47 months before conception and the twentieth week of gestation. At least one of these prescriptions 48 49 21 had to be redeemed between conception and the twentieth week of gestation. 50 51 22 We assessed exposure to betablockers by identifying redeemed prescriptions with ATC code C07. 52 53 23 Furthermore, we identified the most frequently redeemed betablockers in Denmark: labetalol 54 55 24 (C07AG01), metoprolol (C07AB02), atenolol (C07AB03), propranolol (C07AA05), pindolol 56 57 58 59 5 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 29 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 (C07AA03), and sotalol (C07AA07). Fewer than 50 pregnancies were exposed to any of the 5 6 2 remaining betablockers. 7 8 3 We divided betablocker exposure into exposure to labetalol and exposure to other beta 9 10 11 4 blockers. The latter group was formed because there were few redeemed prescriptions of individual 12 13 5 betablockers other than labetalol. We compared risks associated with exposure to betablockers 14 15 6 with exposure toFor methyldopa peer (C02AB01, C02AB02), review calcium channel only blockers (C08C), and ACE 16 17 7 inhibitors (C09A) to assess possible confounding by indication. 18 19 20 8 Maternal diabetes mellitus was defined as redeeming a prescription for insulin or an insulin 21 22 9 analogue (ATC code A10A). Furthermore, we assessed comedication with statins (ATC code C10) 23 24 10 and antiobesity drugs (ATC code A08A). We identified pregnant women redeeming prescriptions 25 26 11 with these drugs in order to adjust for diabetes mellitus, obesity, and statin use since these women 27 28 12 have different risk profiles for the defined outcomes. 29 30 31 13 32

33 14 Definition of Outcomes http://bmjopen.bmj.com/ 34 35 15 Being born SGA was defined as having a birth weight below the tenth percentile for the 36 37 th 38 16 corresponding gestational week. Preterm birth was defined as birth before the 37 gestational week. 39 40 17 Perinatal mortality was defined as either death occurring within the first 28 days of life, or stillbirth.

41 on September 26, 2021 by guest. Protected copyright. 42 18 Before 2004, foetal deaths were recorded as stillbirths if they occurred after 28 weeks of gestation, 43 44 19 but since then stillbirth is recorded for deaths after 22 gestational weeks.[20] 45 46 47 20 48 49 21 Statistical analyses 50 51 22 Data were managed and analysed using SAS 9.2 (SAS Institute Inc., Cary, NC, USA). Logistic 52 53 23 54 regression models were developed for dichotomous variables adjusted for maternal age, year of 55 56 24 conception, annual household income, parity, and educational level (model 1). Maternal age was 57 58 59 6 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 30 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 divided into five groups: <20, 2125, 2630, 3135, >35 years (no missing values). Annual 5 6 2 household income at year of birth was divided into quartiles (1266 missing values). Subjects were 7 8 3 divided into quartiles according to the number of previous births, including stillbirths (37 missing 9 10 11 4 values): 0, 1, 2, ≥3 births. Year of conception was ordered into three categories (19941998, 1999 12 13 5 2003, and 20042008). Educational level was divided into tertiles by highest level of education 14 15 6 achieved at the Foryear of birth. peer For missing information review we used information only from the following 16 17 7 calendar year (32 745 missing values). 18 19 20 8 We constructed a separate logistic regression model (model 2) including the socioeconomic 21 22 9 variables in model 1 and additional confounding variables: smoking status, comedication (yes/no) 23 24 10 with statins, antiobesity drugs, insulin and insulin analogues, and diagnoses of pre 25 26 11 eclampsia/eclampsia. These confounders were included in model 2 due to the high frequency of 27 28 12 missing data, because information on smoking and diagnoses of preeclampsia/eclampsia were not 29 30 31 13 available for the years 1995 and 2008. Maternal smoking was divided into four categories according 32

33 14 to the number of cigarettes smoked daily (0, 110, 1120, >20). http://bmjopen.bmj.com/ 34 35 15 When estimating the risk of perinatal mortality, analyses were further adjusted for previous 36 37 16 stillbirths. Odds ratios are presented with 95% confidence intervals (95% CIs). For description of 38 39 40 17 basic characteristics we used frequencies with percentages. We used Chisquare tests to analyse

41 on September 26, 2021 by guest. Protected copyright. 42 18 differences in the proportions of the different classes of categorical baseline characteristics. 43 44 19 Statistical significance was defined as p<0.05. All tests were twosided. 45 46 20 In addition, we carried out a propensity scorematched regression analysis to consolidate our 47 48 21 findings. We calculated a propensity score for the likelihood of redeeming a betablocker during 49 50 51 22 pregnancy by multivariate logistic regression conditional on baseline covariates. Using the Greedy 52 53 23 matching macro (http://mayoresearch.mayo.edu/mayo/research/biostat/upload/gmatch.sas), we 54 55 24 matched each case to four controls on the basis of the propensity score (table 1). We did not match 56 57 58 59 7 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 31 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 on diagnoses of preeclampsia/eclampsia since a large fraction of these cases redeemed betablocker 5 6 2 prescriptions. 7 8 3 9 10 11 4 12 RESULTS 13 14 5 Table 1 presents maternal characteristics in betablockerexposed and unexposed women (number 15 For peer review only 16 17 6 and percentage of pregnancies). We identified 2381 pregnancies exposed to only one betablocker, 18 19 7 1452 exposed to labetalol only, and 929 exposed to other betablockers. 98 pregnancies were 20 21 8 exposed to more than one betablocker. We found 515 pregnancies exposed to methyldopa, 86 22 23 9 pregnancies to calcium channel blockers (CCBs), and 48 pregnancies exposed to ACE inhibitors. 24 25 26 10 Women exposed to betablockers during pregnancy were older, had higher income, and higher 27 28 11 parity than unexposed women. The proportions of women redeeming prescriptions for statins, 29 30 12 antiobesity preparations, and insulins were higher among the betablockerexposed group. The 31 32 13 proportion of pregnancies complicated by preeclampsia was higher among betablockerexposed

33 http://bmjopen.bmj.com/ 34 14 35 pregnancies. There was no difference in smoking prevalence between betablockerexposed and 36 37 15 unexposed women (table 1). 38 39 40 16

41 on September 26, 2021 by guest. Protected copyright. 42 17 43 44 18 45 46 19 47 48 20 49 50 21 51 52 22 53 54 23 55 56 24 57 58 59 8 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 32 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 5 6 2 7 8 3 9 10 4 11 12 5 13 14 6 Beta-blocker-exposed Beta-blocker-unexposed Propensity matched 15 For peer review only 16 Table 1. Basic characteristics for pregnancies exposed to betablockers, compared with unexposed 17 pregnancies and propensity scorematched pregnancies. 18 19 (n=2459) (n=909228) (n=9662) 20 Characteristics n (%) n (%) p-valuea n (%) p-valuea 21 Educational level <0.001 0.991 22 Low 739 (30.05) 311 600 (35.45) 2965 (30.69) 23 Medium 972 (39.53) 285 450 (32.47) 3883 (40.19) 24 High 707 (28.75) 279 431 (31.79) 2814 (29.12) 25 26 Annual household income (GBP) <0.001 0.989 27 0 36 770 509 (23.99) 226 228 (24.84) 1924 (19.91) 28 36 771 – 52 703 594 (24.16) 227 195 (24.96) 2337 (24.19) 29 52 704 – 74 699 662 (26.92) 227 089 (24.94) 2631 (27.23) 30 ≥ 74 700 693 (28.18) 227 448 (24.98) 2770 (28.67) 31 Parity <0.001 0.998 32 1 900 (36.60) 394 661 (43.29) 3487 (28.87) 33 http://bmjopen.bmj.com/ 34 2 918 (37.33) 338 989 (37.18) 3658 (30.28) 35 3 455 (18.50) 129 482 (14.20) 1788 (14.80) 36 >3 186 (7.56) 46 057 (5.05) 729 (6.04) 37 Age (years) <0.001 1.000 38 <20 18 (0.73) 26 321 (2.89) 68 (0.56) 39 2125 174 (7.07) 147 298 (16.16) 699 (5.79) 40 2630 700 (28.47) 350 105 (38.40) 2757 (22.82)

41 on September 26, 2021 by guest. Protected copyright. 42 3135 930 (37.82) 281 154 (30.84) 3665 (30.34) 43 >35 637 (24.90) 104 339 (11.44) 2473 (20.47) 44 Daily cigarettesb 0.427 0.385 45 0 1548 (80.29) 572 642 (81.15) 6140 (81.81) 46 110 251 (13.02) 90 033 (12.76) 913 (12.16) 47 1120 114 (5.19) 36201 (5.13) 394 (5.25) 48 >20 15 (0.78) 4849 (0.69) 59 (0.79) 49 50 Statins <0.001 0.492 51 Used 5 (0.20) 111 (0.01) 14 (0.14) 52 Not used 2454 (99.8) 909 115 (99.99) 9648 (99.86) 53 Antiobesity preparations (A10) 0.018 0.251 54 55 Used 9 (0.40) 1539 (0.17) 23 (0.24) 56 Not used 2450 (99.6) 907 687 (99.83) 9639 (99.76) 57 58 59 9 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 33 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 Insulins and analogues <0.001 0.782 5 Used 101 (4.11) 4208 (0.46) 412 (4.14) 6 Not used 2358 (95.89) 905 018 (99.53) 9250 (95.74) 7 8 Pre-eclampsia diagnosis(O13-O15) <0.001 9 Yes 99 (4.03) 7806 (0.86) 10 No 2360 (95.97) 901 420 (99.14) 11 1 12 a 13 2 Chisquare tests were used to assess the overall p value for the group comparison. 14 15 bInformation onFor smoking was peer only available forreview 19962007. only 16 3 17 18 19 4 Women redeeming labetalol prescriptions were older, had a higher education level, and a 20 21 5 higher prevalence of preeclampsia and smoking than women exposed to other betablockers (table 22 23 6 2). The proportion of women redeeming prescriptions for insulin was larger among the labetalol 24 25 7 exposed group. There was no difference in income or comedication with statins and antiobesity 26 27 8 28 preparations between the two groups. Diagnoses of migraine and arrhythmias were more common 29 30 9 among women exposed to any other betablocker. Women exposed to other betablockers had 31 32 10 higher parity than those exposed to labetalol.

33 http://bmjopen.bmj.com/ 34 Table 2. Basic characteristics for pregnancies exposed to labetalol, 35 11 36 compared with pregnancies exposed to other betablockers. 37 38 39 Labetalol Other betablockers 40 (n=1452) (n=929) a

41 Characteristics n (%) n (%) pvalue on September 26, 2021 by guest. Protected copyright. 42 Educational level <0.001 43 44 Low 391 (26.93) 321 (34.55) 45 Medium 571 (39.33) 369 (39.72) 46 High 462 (31.82) 226 (24.33) 47 48 Annual household income (GBP) 0.138 49 0 – 36 770 202 (13.91) 289 (31.11) 50 36 771 – 52 703 223 (15.36) 357 (38.43) 51 52 704 – 74 699 228 (15.70) 413 (44.46) 52 53 ≥74 700 275 (19.94) 393 (42.30) 54 Parity 0.004 55 0 512 (35.26) 363 (39.07) 56 1 586 (40.36) 308 (33.15) 57 58 59 10 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 34 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 2 256 (17.63) 179 (19.27) 5 ≥3 98 (6.75) 79 (8.50) 6 7 Age (years) <0.001 8 <20 7 (0.58) 10 (1.08) 9 2125 69 (4.75) 97 (10.44) 10 11 2630 406 (27.96) 275 (29.60) 12 3135 586 (40.36) 314 (33.79) 13 >35 384 (26.45) 233 (25.08) 14 Daily cigarettesb <0.001 15 For peer review only 16 0 933 (64.26) 565 (60.82) 17 110 130 (8.95) 112 (12.06) 18 1120 44 (3.03) 62 (6.67) 19 >20 9 (6.19) 6 (0.65) 20 21 Antiobesity drugs 0.052 22 Yes 5 (0.34) 9 (0.97) 23 No 1447 (99.66) 920 (99.03) 24 25 Statins 0.261 26 Yes 5 (0.34) 1 (0.10) 27 No 1447 (99.66) 928 (99.90) 28 Insulins and analogues <0.001 29 30 Yes 136983 (5.72) 16 (1.72) 31 No 831369 (94.28) 913 (92.28) 32 Migraine <0.001 33 Yes 26 (1.79) 46 (4.95) http://bmjopen.bmj.com/ 34 35 No 1426 (98.21) 883 (95.05) 36 Pre-eclampsia 37 diagnosis 0.001 38 1378 (94.90)74 39 Yes (5.10) 908 (97.84)21 (2.26) 40 74 (5.10) 1378 No (94.90) 21 (2.26)908 (97.84)

41 on September 26, 2021 by guest. Protected copyright. 42 Arrhythmia <0.001 43 Yes 23 (1.58) 82 (8.83) 44 45 No 1429 (98.42) 847 (91.17) 46 Essential tremor 0.030 47 Yes 3 (0.33) 48 No 1452 (100) 926 (99.67) 49 50 1 aChi square tests were used to assess the overall p value for the group 51 52 comparison.

53 2 b 54 Information on smoking was only available for 19962007. 55 3 56 57 58 59 11 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 35 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 Table 3 presents ORs with 95% CIs for SGA, preterm birth and perinatal death for exposure 5 6 2 to betablockers during pregnancy. 7 8 3 9 10 11 4 SGA 12 13 5 We found 93 662 children born SGA in the unexposed population (table 3). There were 446 14 15 6 children born SGAFor among pregnanciespeer exposed review to some kind of betablocker.only We found a higher 16 17 7 proportion of SGA among women exposed to betablockers compared with unexposed women. 18 19 20 8 Women exposed to labetalol or to other betablockers had similarly higher odds ratios than 21 22 9 unexposed women (table 3). 23 24 10 25 26 27 11 Preterm birth 28 29 12 We identified 109 163 preterm births in the unexposed population (table 3). There were 697 preterm 30 31 13 births among pregnancies exposed to betablockers. We found an association between preterm birth 32

33 14 and betablocker exposure compared with unexposed women. Those exposed to labetalol or to other http://bmjopen.bmj.com/ 34 35 15 betablockers had similarly higher odds ratios than unexposed women (table 3). 36 37 38 16 39 40 17 Perinatal mortality

41 on September 26, 2021 by guest. Protected copyright. 42 18 We identified 6048 perinatal deaths in the unexposed population (table 3). There were 44 perinatal 43 44 45 19 deaths among infants exposed to betablockers. We found a higher rate of perinatal mortality 46 47 20 amongst women exposed to betablockers (table 3). 48 49 21 When stratifying for different betablockers we found 30 perinatal deaths among labetalol 50 51 22 exposed pregnancies. Labetalol exposure was associated with increased risk of perinatal mortality 52 53 23 54 (table 3). 55 56 57 58 59 12 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 36 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 We identified 13 perinatal deaths among pregnancies exposed to other betablockers. 5 6 2 Exposure to other betablockers was found to be significantly associated with perinatal mortality in 7 8 3 the unadjusted model and model 1. However, adjusting our analysis for additional confounding 9 10 11 4 variables (Model 2) rendered the association statistically insignificant (table 3). 12 13 5 14 15 6 Other analysesFor peer review only 16 17 18 7 We identified 515 pregnancies exposed to methyldopa (table 3). We found 61 children born SGA, 19 20 8 216 preterm births and 4 perinatal deaths among these pregnancies. We found a positive association 21 22 9 between children born SGA and exposure to methyldopa, and between methyldopa exposure and 23 24 10 increased risk of preterm birth. Exposure to methyldopa during pregnancy was not significantly 25 26 11 27 associated with perinatal mortality (table 3). 28 29 12 30 31 13 Table 3. ORs with 95% CIs for SGA, preterm birth and perinatal death for exposure to beta 32

33 http://bmjopen.bmj.com/ 14 blockers during pregnancy. 34 35 36 15 37 38 39 40

41 on September 26, 2021 by guest. Protected copyright. 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 13 60

Table 3 Odds RatiosFor (ORs)peer reviewwith 95% only CI for- http://bmjopen.bmj.com/site/about/guidelines.xhtml SGA, preterm birth and perinatal death for exposure to beta-blockers during pregnancy. Page 37 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 Exposure Crude Adjusted (model 1) Adjusted (model 2) 4 N (%) OR (95% CI) OR (95% CI) OR (95% CI) 5 SGA 6 7 Unexposed (n=909 226) 93 662 (10.30) Reference Reference Reference 8 All betablockers (n=2459) 446 (18.14) 1.93 (1.742.14) 1.99 (1.792.21) 1.97 (1.752.23) 9 Labetalol only (n=1452) 258 (17.77) 1.88 (1.642.15) 1.95 (1.702.24) 2.02 (1.722.37) 10 11 Other betablockers (n=929) 179 (19.27) 2.08 (1.762.44) 2.11 (1.792.49) 2.01 (1.662.43) 12 Methyldopa (n= 515) 61 (11.84) 1.17 (0.891.53) 1.32 (1.011.73) 1.43 (1.041.96) 13 CCBs (n=86) 21 (24.42) 2.30 (1.423.73) 2.24 (1.363.67) 1.88 (1.023.49) 14

15 For peer review only 16 Preterm birth 17 Unexposed (n=909 226) 109 163 (12.01) Reference Reference Reference 18 All betablockers (n=2459) 697 (28.34) 2.9 (2.663.14) 2.71 (2.482.97) 2.26 (2.032.52) 19 20 Labetalol only (n=1452) 473 (32.58) 3.54 (3.173.95) 3.33 (2.983.72) 2.74 (2.393.13) 21 Other betablockers (n=929) 206 (22.17) 2.08 (1.782.43) 1.93 (1.652.26) 1.69 (1.412.03) 22 Methyldopa (n= 515) 216 (41.94) 5.29 (4.446.31) 5.03 (4.216.01) 4.21 (3.385.23) 23 CCBs (n=86) 26 (30.23) 2.55 (1.633.99) 2.50 (1.603.89) 2.15 (1.263.67) 24 25 26 Perinatal mortality 27 Unexposed (n=909 226) 6048 (0.67) Reference Reference Reference 28 29 All betablockers (n=2459) 44 (1.79) 2.72 (2.023.67) 2.69 (1.983.65) 1.89 (1.252.84) 30 Labetalol only (n=1452) 30 (2.07) 3.15 (2.194.52) 3.24 (2.254.67) 2.08 (1.263.44) 31 Other betablockers (n=929) 13 (1.39) 2.12 (1.223.66) 1.92 (1.083.40) 1.72 (0.853.48) 32 Methyldopa (n= 515) 4 (0.78) 1.15 (0.433.07) 1.16 (0.433.12) 0.35 (0.052.50)

33 http://bmjopen.bmj.com/ 34 CCBs (n=86) 1 (1.16) 1.78 (0.2512.57) 2.00 (0.2814.83) 3.26 (0.4523.77) 35 1 36 37 2 38 39 3 40 4 41 We found 86 pregnancies exposed to calcium channel blockers (table 3). These included 17 on September 26, 2021 by guest. Protected copyright. 42 43 5 children born SGA, 18 preterm births and 1 perinatal death. We found an association between 44 45 6 exposure to calcium channel blockers and children born SGA in all models. 46 47 48 7 Additionally, we found an association between exposure to calcium channel blockers and 49 50 8 increased risk of preterm birth in all models. As with methyldopa, exposure to calcium channel 51 52 9 blockers during pregnancy was not found to be associated with perinatal mortality (table 3). 53 54 10 Analyses for exposure to ACE inhibitors were not performed since we identified only 48 55 56 11 57 pregnancies exposed to them. 58 59 14 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 38 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 Post hoc we analysed the effect of exposure to all betablockers using a propensity score 5 6 2 matched control group (Table 1) and found similar results to those of the primary analyses: SGA, 7 8 3 OR=1.93 (95% CI, 1.71–2.19); preterm birth, OR=2.40 (95% CI, 2.16–2.67); perinatal mortality, 9 10 11 4 OR=3.22 (95% CI, 2.15–4.82). 12 13 5 14 15 6 DISCUSSION For peer review only 16 17 7 In the present study, which we believe to be the largest of its kind to date, we found an association 18 19 8 20 between redeeming prescriptions of betablockers during pregnancy and being born SGA, preterm 21 22 9 birth, and perinatal mortality. In addition, we found an association between redeeming prescriptions 23 24 10 of methyldopa and calcium channel blockers, being born SGA, and preterm birth. Methyldopa and 25 26 11 calcium channel blockers were not found to be associated with perinatal mortality. 27 28 12 We found exposure to any betablocker to be associated with being born SGA. Our results are 29 30 31 13 in accordance with a recent study reporting increased risk of being born SGA among pregnancies 32

33 14 exposed to selective betablockers (OR=6.00; 95% CI, 1.06–33.87) and labetalol (OR=2.26; 95% http://bmjopen.bmj.com/ 34 35 15 CI, 1.04–4.88).[9] Labetalol is generally considered safe for use during pregnancy.[1,8,21] 36 37 16 38 39 40 17 Exposure to betablockers was found to be associated with preterm birth. When stratifying for

41 on September 26, 2021 by guest. Protected copyright. 42 18 different betablockers we found an increased risk of preterm birth after exposure to labetalol, and 43 44 19 all other betablockers, respectively. 45 46 20 We found an association between exposure to betablockers and perinatal mortality. When 47 48 49 21 stratifying for different betablockers we found this association to be statistically significant for 50 51 22 exposure to labetalol and other betablockers. When adjusting our analysis for maternal co 52 53 23 morbidity, comedication, and smoking, only labetalol was found to be associated with perinatal 54 55 24 mortality. 56 57 58 59 15 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 39 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 Methyldopa is mainly used to treat chronic hypertension during pregnancy as firstline 5 6 2 therapy.[1] Previous studies did not find any associations between methyldopa exposure and being 7 8 3 born SGA or preterm birth.[1,3] Methyldopa has not been found to have effects on placental 9 10 11 4 haemodynamics.[1] However, a recent casecontrol study reported an increased risk of being born 12 13 5 SGA among pregnancies exposed to centrally acting adrenergic agents during the second and third 14 15 6 trimesters[9]: OR=1.70For (95% peer CI, 1.00–2.89). review We found that methyldopa only exposure was associated 16 17 7 with being born SGA and preterm birth. This could be due to indicative antihypertensive treatment 18 19 20 8 with methyldopa in pregnant women with diabetes or pregnancy related diabetes. The prevalence of 21 22 9 diabetes among methyldopaexposed pregnancies was found to be higher: 11.1% compared with 23 24 10 3.9% among betablockerexposed pregnancies. Increased risk of preterm birth was still seen after 25 26 11 adjusting our analyses for additional confounding variables in model 2. We found no association 27 28 12 between exposure to methyldopa and perinatal mortality. These findings are consistent with those of 29 30 31 13 a previous study.[3] 32

33 14 Calcium channel blockers are considered to be safe during pregnancy.[3,22] We found that http://bmjopen.bmj.com/ 34 35 15 exposure to calcium channel blockers was associated with being born SGA and with preterm birth. 36 37 16 The risk of being born SGA and preterm of birth remained after adjusting our analyses for 38 39 40 17 additional confounding variables in model 2. We found no statistically significant association

41 on September 26, 2021 by guest. Protected copyright. 42 18 between calcium channel blocker exposure during pregnancy and perinatal mortality. 43 44 19 We chose to analyse two outcomes previously reported to be associated with betablocker 45 46 20 exposure during pregnancy —SGA and preterm birth[1,10,23] — that have been associated with 47 48 21 increased perinatal mortality in previous studies.[12,13] Therefore we investigated the risk of 49 50 51 22 perinatal mortality among betablockerexposed pregnancies. We compared risks associated with 52 53 23 exposure to betablockers with exposure to methyldopa and calcium channel blockers to assess 54 55 24 possible confounding by indication. Our analyses show a similar risk of being born SGA and an 56 57 58 59 16 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 40 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 increased risk of preterm birth for all recommended agents during pregnancy. There are various 5 6 2 possible explanations for this finding. It is possible that the underlying indication for treatment, 7 8 3 maternal disease, is the true risk factor. Possible maternal diseases include hypertension, either 9 10 11 4 predating or complicating pregnancy. Accordingly, we were not able to rule out a potential effect of 12 13 5 maternal disease on perinatal outcomes. 14 15 6 We foundFor an association peer between exposure review to betablockers onlyduring pregnancy and perinatal 16 17 7 mortality. This association was not found for exposure to methyldopa and calcium channel 18 19 20 8 blockers, which might be due to the small number of cases. 21 22 9 We believe that the similar risks found for exposure to the various betablockers and SGA, 23 24 10 preterm birth, and perinatal mortality are a class effect. This seems to be true in spite of statistically 25 26 11 significant differences in the basic characteristics of women exposed to labetalol and those exposed 27 28 12 to other betablockers (table 2). After adjustments were made for these variables, we found 29 30 31 13 comparable risk profiles for labetalolexposed pregnancies and pregnancies exposed to other beta 32

33 14 blockers. Most betablockers are known to cross the placenta,[21,24] and effects on placental http://bmjopen.bmj.com/ 34 35 15 haemodynamics have been observed in both human and animal studies. A mechanism has been 36 37 16 proposed of diminished placental blood flow due to the selective vasoconstriction of placental 38 39 40 17 vessels by betablockers without intrinsic sympathomimetic activity.[24] This effect on placental

41 on September 26, 2021 by guest. Protected copyright. 42 18 haemodynamics could explain growth retardation of foetuses exposed to betablockers during 43 44 19 pregnancy and might result in children being born SGA and preterm. 45 46 20 We defined exposure as redemption of at least two prescriptions between six months before 47 48 21 conception and the twentieth week of gestation. At least one of these prescriptions had to be 49 50 51 22 redeemed between conception and twentieth week of gestation. We believe that this model 52 53 23 increases the probability of identifying continuous use that extends into pregnancy. 54 55 56 57 58 59 17 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 41 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 The rate of perinatal mortality in Denmark is low (table 3).[25] A large number of women 5 6 2 exposed to betablockers, methyldopa, and calcium channel blockers are therefore needed to 7 8 3 identify a possible risk increase associated with these outcomes. Our cohort comprises all births in 9 10 11 4 Denmark between 1995 and 2008. This minimises confounding due to race, educational level, and 12 13 5 other socioeconomic factors. The national Danish registers cover the entire nation and are 14 15 6 considered valid.For As part of peerthe national health review care reimbursement only scheme, Danish pharmacies are 16 17 7 required by law to register all redeemed prescriptions. Approximately 97.5% of all redeemed 18 19 20 8 prescriptions are registered in the Danish Prescription register.[16] Our study includes data on 21 22 9 exposure to betablockers based on information on prescriptions paid for at the pharmacy, and not 23 24 10 only prescribed by the physician, thereby increasing the probability of exposure. Furthermore, our 25 26 11 study was not confounded by recall bias since information was recorded prospectively. The Danish 27 28 12 Fertility Database contains more than 99% of all births during the study period.[14] 29 30 31 13 Limitations of our study include missing information on maternal weight and alcohol 32

33 14 consumption. We were unable to adjust for treatment indication and severity of maternal disease. http://bmjopen.bmj.com/ 34 35 15 Given the study design, we were not able to address this issue further, nor were we able to rule out 36 37 16 confounding by indication, the underlying maternal disease, as a possible explanation for our 38 39 40 17 findings. Consequently we were unable to differentiate between a possible class effect of beta

41 on September 26, 2021 by guest. Protected copyright. 42 18 blockers and the effect of the underlying maternal disease. 43 44 19 Unfortunately information on diagnoses of essential hypertension was not available, since 45 46 20 these are known risk factors for our primary outcomes. 47 48 21 The prevalence of preeclampsia and eclampsia in the cohort is based on primary discharge 49 50 51 22 diagnoses from hospital admissions. We did not use secondary diagnoses, since these in general are 52 53 23 not validated. We estimated exposure from National Prescription Registry data, which contains 54 55 24 information on all redeemed prescriptions.[16] Overestimation of exposure is therefore a 56 57 58 59 18 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 42 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 possibility, since we cannot adjust for a potential lack of compliance. However, in a study by 5 6 2 Olesen et al. conducted in a cohort of pregnant Danish women in the county of North Jutland,[26] 7 8 3 compliance with prescribed betablockers was estimated to be complete, strengthening the validity 9 10 11 4 of our analyses. Furthermore, overestimation of exposure would bias the estimates towards unity. 12 13 5 There is a general consensus that labetalol is safer than other betablockers during pregnancy 14 15 6 and this drug is Forrapidly becoming peer the firstline review choice in conditions only such as chronic hypertension 16 17 7 during pregnancy.[21,23] We found an association between redeeming prescriptions for beta 18 19 20 8 blockers and being born SGA, preterm birth, and perinatal mortality. Risk profiles for pregnancies 21 22 9 exposed to labetalol and to other betablockers were similar. Our findings therefore suggest that 23 24 10 future treatment of pregnant women with betablockers should be based primarily on the individual 25 26 11 needs of the mother and not of the unborn child. The increasing use and uncertainty of effects and 27 28 12 possible side effects of treatment with betablockers during pregnancy call for further studies to 29 30 31 13 validate our findings. 32

33 14 http://bmjopen.bmj.com/ 34 35 15 Conflicts of interests 36 37 16 The authors have no relevant conflict of interests. 38 39 40 17

41 on September 26, 2021 by guest. Protected copyright. 42 18 Funding 43 44 19 The project was sponsored by the Capital Region of Copenhagen. 45 46 20 47 48 21 49 50 22 REFERENCES 51 52 53 23 1 Sibai BM. Treatment of hypertension in pregnant women. N Engl J Med 1996 Jul 54 55 24 25;335(4):25765. 56 57 58 59 19 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml Page 43 of 45 BMJ Open BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 2 Magee LA, Ornstein MP, von DP. Fortnightly review: management of hypertension in 5 6 2 pregnancy. BMJ 1999 May 15;318(7194):13326. 7 8 9 3 3 Afifi Y, Churchill D. Pharmacological treatment of hypertension in pregnancy. Curr Pharm 10 11 12 4 Des 2003;9(21):174553. 13 14 15 5 4 Magee LA,For Duley L.peer Oral betablockers review for mild to moderate only hypertension during 16 17 6 pregnancy. Cochrane Database Syst Rev 2003;(3):CD002863. 18 19 20 7 5 Modi S FAU Lowder D, Lowder DM. Medications for migraine prophylaxis.(0002838X 21 22 8 23 (Print)). 24 25 26 9 6 Lyons KE FAU Pahwa R, Pahwa R. Pharmacotherapy of essential tremor : an overview of 27 28 10 existing and upcoming agents.(11727047 (Print)). 29 30 31 11 7 Sibai BM, Gonzalez AR, Mabie WC et al. comparison of labetalol plus hospitalization 32

33 12 versus hospitalization alone in the management of preeclampsia remote from term. Obstet http://bmjopen.bmj.com/ 34 35 36 13 Gynecol 1987 Sep;70(3 Pt 1):3237. 37 38 39 14 8 Magee LA, Elran E, Bull SB et al. Risks and benefits of betareceptor blockers for 40

41 15 pregnancy hypertension: overview of the randomized trials. Eur J Obstet Gynecol Reprod on September 26, 2021 by guest. Protected copyright. 42 43 16 Biol 2000 Jan;88(1):1526. 44 45 46 17 9 NakhaiPour HR, Rey E, Berard A. Antihypertensive medication use during pregnancy and 47 48 49 18 the risk of major congenital malformations or smallforgestationalage newborns. Birth 50 51 19 Defects Res B Dev Reprod Toxicol 2010 Apr;89(2):14754. 52 53 54 20 10 Lydakis C, Lip GY, Beevers M et al. Atenolol and foetal growth in pregnancies complicated 55 56 21 by hypertension. Am J Hypertens 1999 Jun;12(6):5417. 57 58 59 20 60

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml BMJ Open Page 44 of 45 BMJ Open: first published as 10.1136/bmjopen-2012-001185 on 19 July 2012. Downloaded from 1 2 3 4 1 11 Abalos E, Duley L, Steyn DW et al. Antihypertensive drug therapy for mild to moderate 5 6 2 hypertension during pregnancy. Cochrane Database Syst Rev 2007;(1):CD002252. 7 8 9 3 12 Zeitlin J, El AM, Jarreau PH et al. Impact of foetal growth restriction on mortality and 10 11 12 4 morbidity in a very preterm birth cohort. J Pediatr 2010 Nov;157(5):7339. 13 14 15 5 13 Challis JR,For Lye SJ, Gibbpeer W et al. Understanding review preterm labor.only Ann N Y Acad Sci 2001 16 17 6 Sep;943:22534. 18 19 20 7 14 Knudsen LB. The Danish Fertility Database. Dan Med Bull 1998 Apr;45(2):2215. 21 22 23 8 15 Andersen TF, Madsen M, Jorgensen J et al. The Danish National Hospital Register. A 24 25 26 9 valuable source of data for modern health sciences. Dan Med Bull 1999 Jun;46(3):2638. 27 28 29 10 16 Gaist D, Sorensen HT, Hallas J. The Danish prescription registries. Dan Med Bull 1997 30 31 11 Sep;44(4):4458. 32

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41 on September 26, 2021 by guest. Protected copyright. 42 15 Jul;39(7 Suppl):914. 43 44 45 16 19 Pedersen CB, Gotzsche H, Moller JO et al. The Danish Civil Registration System. A cohort 46 47 17 of eight million persons. Dan Med Bull 2006 Nov;53(4):4419. 48 49 50 18 51 20 Knudsen LB, Borlum KF. Monitoring perinatal mortality and perinatal care with a national 52 53 19 register: content and usage of the Danish Medical Birth Register. Community Med 1986 54 55 20 Feb;8(1):2936. 56 57 58 59 21 60

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