Main findings

We evaluated most registered live births to Indian immigrants to Canada for more than 2 decades, and compared these births to nearly all live births to Canadian-born parents. Among Indian immigrants, high M:F ratios were observed at third-order and fourth or higher-order births, which did not vary considerably across provinces. We conservatively estimated that 4472 daughters of Indian immigrants to Canada were unaccounted for over the last 2 decades - so-called "missing girls"7-9 - largely among couples of 2 Indian-born parents (89.4%), but also among couples including 1 Canadian-born parent.

Our findings highlight the magnitude of the skewed sex ratios at birth among Indian immigrants to Canada but do not explain them. There are numerous speculations regarding the factors that may affect natural sex ratios, most of which are surrounded by conflicting evidence.18 Human intervention, in the form of prenatal sex selection, specifically induced abortion of female fetuses after prenatal ultrasonography, is the most commonly cited explanation in settings where son preference and strong patriarchal cultures are prevalent, although direct evidence of such a link remains scarce.2,20 Our companion paper adds plausibility to such a claim by showing that high M:F ratios are associated with preceding induced abortions in Ontario.21 Because son-biased sex ratios among Indian immigrants did not differ according to Canadian province in this study, those Ontario findings are likely to apply to the rest of Canada. A qualitative study supports the link between son preference and prenatal sex selection among Indian immigrants in the United States,22 not limited to induced abortion but also involving assisted reproductive technologies. Future studies may further elucidate the specific contribution of the distinct pathways leading to sex-biased ratios at birth.

It appears that skewed M:F ratios among some Indian immigrants to Canada have been present for at least 2 decades, accruing about 4472 "missing girls." This estimate may be conservative, because calculations of the deficit in the number of girls based on M:F ratios do not account for repeated induced abortions of female fetuses.21 Since the biological probability of having a male live birth is independent of the sex of the previous births of the same mother,23 consecutive pregnancies of female fetuses are likely to occur. Some couples may, therefore, undergo repeated induced abortions until they carry a male fetus.21,22 Our study confirms that most of the deficit of girls occurs at the third birth (n = 2616, 58.5%). However, the deficit of girls is higher among fourth and higher-order births (n = 1092, 24.4%) than among second-order births (n = 764, 17.1%), despite the larger number of second-order births. Few previous studies were large enough to examine M:F ratios at fourth and higher-order births.6,13 Unlike in our previous study that was limited to Ontario, and in which we included live and stillbirths in defining birth order,13 here we only included live births. Counting stillbirths dilutes the association between birth order and M:F ratios, since fertility decisions are thought to be made based on the current number and sex of the living children in the family.1

We found increasing temporal trends in the M:F ratio at the third birth paralleled by decreasing trends at higher-order births. This is likely a function of declining trends in family size over time. Under the hypothesis of the son preference, securing a boy by the third birth may release the pressure of getting a boy in subsequent births, although some couples may still recourse to induced abortions to control family size after having had a son.2 The lack of substantial provincial differences in the sex ratios of births to Indian immigrants suggests that the place of origin may be more influential than that of destination. Although the M:F ratio at the fourth birth was somewhat higher in British Columbia, Manitoba and Saskatchewan than in Ontario - something worthy of further exploration - it was higher than expected in all Canadian provinces, suggesting that our findings may be generalized to similar Indian diasporas. Finally, our study quantified the contribution of both maternal and paternal country of birth to M:F newborn sex ratios. Paternal influence has been postulated to be a key influence on M:F ratios,24 and our findings suggest that this is so even among couples of mixed nativity. Certainly, some Canadian-born mothers may have been of second-generation Indian ancestry. Data from the 2001 and 2006 Canadian censuses reported a M:F ratio of 1.32 within households of "Asian" couples with 2 previous girls, in which one or both parents were Canadian-born.11 Interestingly, among mixed nativity couples, most parents in the "Other" group (i.e., not born in Canada or India) were born in the UK, where a large Indian diaspora exists, including second-generation Indians. Further studies may clarify to what extent the skewed sex ratios among mixed nativity couples involve second-generation Indians. Although mixed nativity couples accounted for only 10.6% of the total deficit of girls in the current study, it remains to be seen how M:F ratios will change within this emerging demographic group.19