DOI: 10.1111/j.1471-0528.2008.02058.x Epidemiology www.blackwellpublishing.com/bjog The effect of maternal alcohol consumption on fetal growth and preterm birth CM O’Leary,a N Nassar,a JJ Kurinczuk,b C Bowera a Division of Population Sciences, Telethon Institute for Child Health Research, Centre for Child Health Research, University of Western Australia, Perth, WA, Australia b National Perinatal Epidemiology Unit, University of Oxford, Headington, Oxford, UK Correspondence: Ms CM O’Leary, Division of Population Sciences, Telethon Institute for Child Health Research, Centre for Child Health Research, University of Western Australia, PO Box 855, West Perth, WA 6872, Australia. Email [email protected] Accepted 26 October 2008. Objective To investigate the relationship between prenatal alcohol association between alcohol intake and SGA infants was exposure and fetal growth and preterm birth and to estimate the attenuated after adjustment for maternal smoking. Low levels of effect of dose and timing of alcohol exposure in pregnancy. prenatal alcohol were not associated with preterm birth; however, binge drinking resulted in a nonsignificant increase in odds. Design A population-based cohort study linked to birth Preterm birth was associated with moderate and higher levels of information on the Western Australian Midwives Notification prenatal alcohol consumption for the group of women who System. ceased drinking before the second trimester. This group of Setting Western Australia. women was significantly more likely to deliver a preterm infant than women who abstained from alcohol (adjusted OR 1.73 [95% Population A 10% random sample of births restricted to CI 1.01–3.14]). nonindigenous women who had delivered a singleton infant (n = 4719) in 1995–1997. Conclusions Alcohol intake at higher levels, particularly heavy and binge drinking patterns, is associated with increased risk Methods The impact of alcohol consumption in pregnancy on of preterm birth even when drinking is ceased before the fetal growth (small-for-gestational-age [SGA] and large-for- second trimester. This finding, however, is based on small gestational-age infants [LGA]) and preterm birth (<37 weeks of numbers and needs further investigation. Dose and timing of gestation) was assessed using multivariate logistic regression prenatal alcohol exposure appears to affect preterm delivery analysis and adjusting for confounding factors. andshouldbeconsideredinfutureresearchandhealth Main outcome measures Odds ratios and 95% CI, attributable education. risk, and population attributable risk were calculated. Keywords Fetal growth, high risk, pregnancy, prenatal alcohol Results The percentage of SGA infants and preterm birth increased exposure, preterm birth, RASCALS, small for gestational age. with higher levels of prenatal alcohol exposure; however, the Please cite this paper as: O’Leary C, Nassar N, Kurinczuk J, Bower C. Impact of maternal alcohol consumption on fetal growth and preterm birth. BJOG 2009;116:390–400. Introduction tions, which prevented their results from being generalised to the wider community. The evidence surrounding the effect of low to moderate In the few studies that have reported an association intake of alcohol during pregnancy on fetal growth and pre- between low levels of prenatal alcohol exposure and fetal term birth is inconclusive. While there is a large body of growth, the direction of the association has not been consis- literature on the issue, the evidence base has many weaknesses tent. While the majority of studies have reported no associa- limiting our ability to reach definitive conclusions. In their tion with less than 72 g of alcohol per week (equivalent to systematic review of the literature, Henderson et al. (2007)1 seven standard drinks per week in Australia; six in the reported that many studies did not control for known con- USA, Canada, and Europe; and nine units in the UK) and founding factors, such as cigarette smoking and ethnicity. In low birthweight,3–9 intrauterine growth restriction,5,10,11 and their more detailed report,2 the authors found that the studies preterm birth,8,10,12–17 a small number of studies found an that had adjusted for confounding factors had other limita- increased risk at low levels18–20 and, conversely, others have 390 ª 2009 The Authors Journal compilation ª RCOG 2009 BJOG An International Journal of Obstetrics and Gynaecology The effect of prenatal alcohol on fetal outcomes reported a possible protective effect of low levels of alcohol or never) and the quantity consumed (e.g. number of cans, consumption in pregnancy.10,13,18,21–23 At higher levels of pre- glasses, bottles) on a typical occasion for each of four types of natal alcohol exposure, the findings of an association between alcoholic beverages (beer, wine/champagne, spirits/liqueurs, prenatal alcohol exposure and fetal growth are not consistent, and fortified wines). Consumption frequency calculations with around half of studies reporting no significant associa- used the lower of the days marked, for example 3–4 days/week tion3,4,10,18,24–31 and half reporting a significant associa- was included as 3 days/week to calculate total weekly dose tion.9,20,32–40 Uncertainty also exists about the impact of of alcohol. However, there were a small number of women binge drinking on intrauterine growth and questions remain (n = 7 in first trimester and n = 1 in third trimester) who as to whether the increased risk from binge drinking, if one reported a frequency of drinking of one to two times per week truly exists, is due to the pattern of binge drinking per se or and who consumed two or more types of beverages each at rather a result of heavy alcohol intake.2 less than 50 g per occasion, but with a total weekly consump- Using data from a population-based cohort study of non- tion of 70+ g. As we could not be confident that the women indigenous women in Western Australia (WA), this study had consumed only once per week, and therefore, at binge examines the impact of maternal alcohol consumption, taking levels, we coded them as heavy drinkers. Where respondents into account the quantity per occasion, frequency of con- used a tick mark instead of indicating a numeric value, a sumption, and total quantity consumed during the 3 months minimum level for the type of beverage, time period, and before and during each trimester of pregnancy on preterm frequency was applied. Standard drink calculations were birth and fetal growth. derived during the data analysis stage and covered a range of measures for each type of beverage;42 more details are avail- Materials and methods able on request from the authors. To examine the impact of the pattern of drinking by The details of the study used for this analysis have been women before and during pregnancy, we took into account described previously.41–43 Briefly, a 10% random sample of the frequency, quantity per occasion, and total quantity con- all women giving birth in WA between 1995 and 1997 was sumed. The level of alcohol consumption was categorised into invited by letter at 12 weeks postpartum to participate in five mutually exclusive groups; none, low, moderate, binge a postal survey of health-related behaviours and events during (less than weekly up to twice per week), and heavy (including pregnancy and infancy (subsequently known as the RASCALS women who binged more than twice per week) (Table 1). For study), designed to survey health-related behaviours and the analyses, abstinence during pregnancy refers to women events before and during pregnancy and early infancy. Data who reported not drinking at any stage during pregnancy. were collected using a postal questionnaire sent with the letter One standard drink in Australia is equal to 10 g of alcohol. of invitation. Mothers whose infants were stillborn (n = 20) or The ‘low’ category was defined in line with the 2001 recom- given up for adoption (n = 5) were excluded. An 81% mendation to women who are pregnant or might soon response rate resulted in 4861 completed questionnaires of become pregnant set out by the Australian National Health which 4860 were able to be linked to their corresponding and Medical Research Council alcohol guideline 11, which birth information on the WA Midwives’ Notification System, recommends that ‘If women choose to drink, over a week, a statutory population-based surveillance system of all births should have less than 7 standard drinks, AND, on any one in WA. The analysis reported here was restricted to women day, no more than 2 standard drinks’.45 To assess the overall with singleton births (multiples n = 66) and nonindigenous impact of alcohol intake greater than the low level, moderate, mothers (indigenous n = 75), giving a sample size of 4719. heavy, and binge drinking were also combined. Comparison with data available for all births in WA in this The primary outcomes of the study were the effect of alcohol period44 showed that the respondents were representative of consumption in pregnancy on fetal growth and preterm birth. mothers of all singleton live births with the exception of a slight Appropriate fetal growth was ascertained using the proportion underrepresentation of mothers with low-birthweight babies of optimal birthweight (POBW), where optimal birthweight (5.3% overall versus 4.7% respondents) and mothers aged less was determined after taking into account infant sex, gestational than 20 years (6.0% overall versus 3.6% respondents; 2.5% in this age, maternal height, and parity. The POBW was then calcu- sample). Ethics approval for the conduct of this study was granted lated by taking the ratio of observed birthweight to optimal by the Princess Margaret Hospital Research Ethics Committee birthweight.46 The population selected to define optimal birth- and the WA Confidentiality of Health Information Committee. weight was the total 1998–2002 WA population of singleton, Information about maternal alcohol consumption was col- Caucasian births, not exposed to factors known to influence lected retrospectively for the 3-month period prepregnancy fetal growth pathologically.