According to a new study published in the CMAJ (Canadian Medical Association Journal), mothers who were born in India, but now live in Canada, are considerably more likely to give birth to boys as their second or third births than Canadian women.

Dr. Joel Ray of the St. Michael’s Hospital and University of Toronto remarks:

“Our findings raise questions about why there are more male liveborns than female liveborns among Indian couples who have had two or more previous babies.”

In a male:female ratio study, researchers from St. Michael’s Hospital and the University of Toronto examined 766,688 single live births in Ontario between 2002 and 2007. The births were categorized by the mother’s country or region of birth, revealing that 486,599 babies were born to Canadian mothers, 58,505 to European mothers, 31,978 to Indian mothers and 23,818 to Chinese mothers, whilst 18,971 babies were born to mothers originating from the rest of East Asia, as well as 18,018 Pakistani mothers and 3,663 Korean mothers.

The investigators also considered the fathers country of birth and calculated the male:female ratio of live births by country or region and on how many previous deliveries the mother already had, i.e. 0, 1, 2, 3 or more.

The findings showed that the male:female ratio for most women was 1.05 and remained unchanged, regardless of the number of previous births, yet for Indian and South Korean women with previous children, the likelihood of giving birth to a male child was substantially higher, and even higher than that for Indian-born women with more than one previous child.

According to earlier research in India and a study that examined Canadian census data for South Asian and East Asian immigrants, the patterns of a higher male:female ratios are associated with having more children, in particular, if the previous children were girls.

The authors conclude:

“Whether this difference in sex ratios was the result of prenatal sex selection should be determined by direct study of practices of sex-selected preimplantation and pregnancy termination among individuals from various world regions. In addition, an analysis of the duration of residence in Canada, access to fertility care, family income and parental preferences would be of value in describing factors that might influence prenatal sex selection.”

The study was limited in terms of only including single births, with no consideration to any sex selection in multiple pregnancies from fertility treatments. The researchers were also unable to determine the sex of older siblings from the same mother.

Written By Petra Rate