Sex Ratios at Birth After Induced Abortion
Total Page:16
File Type:pdf, Size:1020Kb
CMAJ Research Sex ratios at birth after induced abortion Marcelo L. Urquia PhD, Rahim Moineddin PhD, Prabhat Jha MD DPhil, Patricia J. O’Campo PhD, Kwame McKenzie MD, Richard H. Glazier MD MPH, David A. Henry MD, Joel G. Ray MD MSc See also www.cmaj.ca/lookup/doi/10.1503/cmaj.160183 and CMAJ Open article www.cmajopen.ca/content/4/2/E116 Abstract Competing interests: None Background: Skewed male:female ratios at birth infants of women who immigrated from India declared. have been observed among certain immigrant and had previously given birth to 2 girls, the This article has been peer groups. Data on abortion practices that might overall male:female ratio was 1.96 (95% confi- reviewed. help to explain these findings are lacking. dence interval [CI] 1.75–2.21) for the third live Accepted: Jan. 8, 2016 birth. The male:female infant ratio after 2 Online: Apr. 11, 2016 Methods: We examined 1 220 933 births to girls was 1.77 (95% CI 1.26–2.47) times higher women with up to 3 consecutive singleton live if the current birth was preceded by 1 induced Correspondence to: births between 1993 and 2012 in Ontario. Marcelo Urquia, abortion, 2.38 (95% CI 1.44–3.94) times higher [email protected] Records of live births, and induced and sponta- if preceded by 2 or more induced abortions neous abortions were linked to Canadian immi- and 3.88 (95% CI 2.02–7.50) times higher if CMAJ 2016. DOI:10.1503 / cmaj.151074 gration records. We determined associations of the induced abortion was performed at male:female infant ratios with maternal birth- 15 weeks or more gestation relative to no pre- place, sex of the previous living sibling(s) and ceding abortion. Spontaneous abortions were prior spontaneous or induced abortions. not associated with male-biased sex ratios in subsequent births. Results: Male:female infant ratios did not appreciably depart from the normal range Interpretation: High male:female ratios among Canadian-born women and most observed among infants born to women who women born outside of Canada, irrespective immigrated from India are associated with of the sex of previous children or the charac- induced abortions, especially in the second tri- teristics of prior abortions. However, among mester of pregnancy. he natural odds of having a male child raphy, particularly among couples with 2 prior — the male:female ratio at birth — is daughters. Differing male:female infant ratios relatively stable across human popula- may also be explained by differential use of T1,2 12 tions. It ranges between 1.03 and 1.07 males pre- and postfertilization techniques, bias in per female, and is largely independent of birth the reporting of live births13 and sex-selective order and the sex of previous siblings.2,3 Modest postnatal infanticide.14 The body of literature to variations in the natural male:female ratio have date reflects mostly indirect evidence obtained been linked to demographic, biologic and envi- by rough measurement of male:female ratios at ronmental factors,2,4–6 including wartime and birth in India,15–17 China,13,18,19 Vietnam20,21 and environmental disasters.7–9 the rest of Asia.22–25 Prior studies of this phe- In certain Asian countries, a higher-than- nomenon in industrialized countries have expected male:female ratio at birth is thought to looked at maternal country of origin broadly be a product of sex discrimination fuelled by but have observed it predominantly among the preference for sons. This preference has Asian immigrants from countries where male- been attributed to various economic and cul- biased infant sex ratios have been extensively tural factors, including provision of financial documented.10,26–30 Data on the relation between support in old age, the burden of dowry pay- abortion practices and male:female infant ratios ments and worship duties in India,10,11 patrilin- are lacking. eal lineage in China and India, and the 1-child Although prenatal sex selection is thought to policy in China.10 One major mechanism occur within certain Asian countries (e.g., behind skewed male:female infant ratios is India),31 differing approaches to interpretation thought to be induced abortion of female of sex ratios at birth has led to some contro- fetuses identified on early prenatal ultrasonog- versy regarding its practice in North America © 2016 Joule Inc. or its licensors CMAJ, June 14, 2016, 188(9) E181 Research and the United Kingdom.32–34 Published studies tion records of all individuals granted permanent rarely considered the sex of the previous sib- residency in Canada since January 1985. The lings — a key determinant of subsequent fertil- immigration database is linked with the Ontario ity decisions35 — nor did they distinguish Registered Persons Database, a registry that con- between women who had induced abortions tains the unique health numbers that have been following live births from those who had not. issued to individuals eligible for coverage under We studied the male:female ratios of liveborn the Ontario Health Insurance Plan (OHIP). children in Ontario, where induced abortions are About 90% of individuals in the immigration both legal and free. Our objective was to evaluate database were matched to a resident of Ontario the male:female ratio at birth in relation to the with a valid health card number. Unmatched mother’s country of birth, the sex and birth order immigrants may have moved out of Ontario or of her children, and the type, number and timing may have been misclassified as nonimmigrants. of any abortions she had between live births. Sociodemographic characteristics did not signifi- cantly differ between matched and unmatched Methods individuals, suggesting little, if any, selection bias among immigrants.36 We assigned 6 groups Study setting and participants by maternal birthplace: born in Canada (group The eligible study population comprised all sin- contains a small proportion of immigrant resi- gleton live births to women residing in Ontario dents who could not be matched to the immigra- at the time of delivery who had a valid Ontario tion registry or who immigrated before 1985), health card number. The study sample was immigrants from India, immigrants from China retrieved from population-based administrative (including Hong Kong, Macau and Taiwan), databases linked at the Institute for Clinical immigrants from other South Asian countries Evaluative Sciences (Toronto) and restricted to (Afghanistan, Bangladesh, Sri Lanka, Pakistan), women who had up to 3 consecutive singleton immigrants from other Asian countries (Iran, live births in Ontario hospitals starting Apr. 1, Nepal, Bhutan, Maldives, Vietnam, Philippines, 1993, of which at least 1 live birth occurred Indonesia, Cambodia, Thailand, Singapore, between Apr. 1, 2002, and Mar. 31, 2012. The Myanmar, Lao People’s Democratic Republic, latter is required because all previous live births Brunei Darussalam, Timor-Leste and Malaysia) would have been reported in the obstetrical and immigrants from the rest of the world. delivery record since Apr. 1, 2002, and this We defined induced abortions as any surgi- number had to agree with the historical count of cal or medication-induced termination of preg- liveborn deliveries to the same mother to accu- nancy. If 2 consecutive abortions were recorded rately measure live-birth order. If the 2 num- within 40 days of each other, they were consid- bers differed, we excluded these women and all ered the same event, and the date of the first of their births to avoid including women with abortion was used. Induced abortions per- incomplete reproductive history. We also formed in a hospital acute care, day surgery or excluded births for which sex of the infant was emergency department setting were captured in unknown, fourth- or higher-order live births the Discharge Abstracts Database, Same-Day- that resulted in sparse data, women whose first Surgery Database and the National Ambulatory birth was before April 1993 and women whose Care Reporting System of the Canadian Insti- country of birth could not be determined. tute for Health Information, under mandatory reporting requirements. To be considered an Variable definitions and data sources induced abortion, a record must have had a pro- We defined birth order as the complete sequence cedure code for a termination of pregnancy of up to 3 consecutive live births from the same without a concomitant diagnostic code for a mother. We updated birth order at each subse- spontaneous abortion (Appendix 1, available quent live birth by removing prior siblings who at www.cmaj.ca/lookup/suppl/doi:10.1503/ were no longer alive by the estimated conception cmaj.151074/-/DC1). Abortions performed date of the current live birth, based on the out of hospital were captured using the OHIP assumption that fertility decisions are based on the physician billing codes for a surgical induced number and sex of the children currently alive. abortion. An induced abortion was classified Alive status was assessed via a linkage with the according to whether it was performed at less death database of the Ontario Office of the Regis- than 15 weeks or at 15 weeks or more gesta- trar General, complemented by in-hospital deaths. tion, based on fee codes S752 and S785, We ascertained maternal birthplace through respectively. Terminations at 15 weeks or more the Citizenship and Immigration Canada perma- are only eligible for payment if gestational age nent resident database, which has the immigra- is confirmed by ultrasonography. E182 CMAJ, June 14, 2016, 188(9) Research Statistical analysis groups, but it varied according to the sex of the The male:female ratio is a particular example of previous sibling(s) (Table 1). Women who had the odds [Pmale/(1 – Pmale)], expressed herein as immigrated from India and who gave birth to a the proportion of males divided by the propor- third child were 2.9 times more likely to have tion of females, at the current (index) delivery.