More boys than expected are born to Indian-born women living in Ontario, Canada, who already have two daughters, according to a large study in CMAJ (Canadian Medical Association Journal). The likelihood of male births increases if women had had an induced abortion before the male birth.

The natural odds of having a boy are in the range of 103 to 107 boys for every 100 girls.

Researchers looked at data on more than 1.2 million births in women with having a third child in Ontario between Apr. 1, 1993, and Mar. 31, 2012. Of the total group, 153 829 (12.6%) were immigrant women from Asia. Data came from the Institute for Clinical Evaluative Sciences (ICES) and the Citizenship and Immigration Canada permanent resident database regarding maternal birthplace.

Among women born in India who already had two girls, the ratio of male to female babies for the third birth was almost double the average, with 196 boys born for every 100 girls. If an Indian-born mother with two daughters had had an abortion before the third child, the sex ratio increased to 326 boys for every 100 girls and to 409 boys if the mother had had multiple abortions. If a woman had an abortion at or after 15 weeks, when ultrasound can determine sex of the fetus, the sex ratio rose further, to 663 boys for every 100 girls.

“Among some Indian immigrants, the practice of induced abortions is associated with subsequently having a boy, especially at the third birth and among women with two previous girls,” states Dr. Marcelo Urquia, St. Michael’s Hospital, Toronto, Ontario, with coauthors.

Birth ratios fell within the natural range for Canadian-born women and immigrant women from most other countries.

Previous studies of male – female birth ratios have relied on indirect evidence, and most have not considered the sex of the existing siblings or the number of abortions as factors.

The researchers suggest that these findings “provide details about specific factors associated with this practice.”

“Further research may clarify the social and cultural forces that influence some immigrant couples to have more more sons than daughters, particularly in the Canadian context, which is a more sex-egalitarian society, and where the given reasons for preferring sons are supposed to be undermined,” they conclude.

In a related commentary, Drs. Abdool Yasseen and Thierry Lacaze-Masmonteil, from the Children’s Hospital of Eastern Ontario,Ottawa, Ontario, write, “[the authors’] results suggest that prenatal sex selection is likely present among first-generation immigrants to Canada from India and provide strong evidence that suggests induced abortions are being used to select infant sex in Canada. We hope that these findings stimulate discussion toward the re-evaluation and development of public health policies aimed at eliminating the practice of prenatal sex selection in Canada.”

“The real question is not whether the practice of prenatal sex selection exists – it is clear from the results of this study and numerous others that it does – but why this practice persists, particularly in a Canadian society that espouses sex equality.”