Contrary to what researchers expected, the length of time Indian immigrants have lived in Canada has no effect whatsoever on the practice of sex selection in favour of boys.

The lead author of an upcoming study, Marcelo Urquia, said his team's findings show Indian mothers are more than twice as likely to have a male third child, if a couple has already had two daughters.

"Families prefer to have boys rather than girls," said Urquia, an assistant professor at the University of Manitoba. "Or, if they already have daughters, they want to have at least one male in the family."

While Canadian-born women give birth to about 105 boys for every 100 girls, Urquia and his team from the University of Toronto and St. Michael's Hospital, showed Punjabi-speaking mothers in Ontario, at their third birth, had 240 boys for every 100 girls.

"We expected that with longer exposure to Canada's environment of greater gender equality, immigrants from India would progressively shift toward valuing daughters and sons more equally," Urquia said. But it seems that's not so.

Instead of finding a decrease, they actually found a slight increase in preference for boys.

For Punjabi-speaking Ontario women new to Canada, Urquia found they give birth to 213 boys to every 100 girls if they have already had two daughters, whereas mothers who have been in Canada for 10 years or more, including those raised in Canada, gave birth to 270 boys to every 100 girls.

Among Indian immigrants, the researchers found sex selection most common in the Punjabi-speaking community but it was also seen in women whose mother tongue was Hindi.

No choice for some moms: director

The new findings are based on 46,834 live births to Indian-born mothers who gave birth in Ontario hospitals between 1993 and 2014 and will be published in an upcoming issue of the Journal of Obstetrics and Gynaecology Canada.

Sex selection with preferences for boys happens across the country, Urquia said.

"But we don't really understand why this is still happening in Canada."

The data were especially puzzling to Urquia and his colleagues because other health trends do change after immigrants live in Canada for years. For example, Indian women who abstained from drinking in India tend to begin consuming alcohol after living in Canada, said Urquia. Also, Indian immigrants tend to become more sedentary when they move to Canada and obesity rates, not surprisingly, rise.

"We don't have a proper explanation," he said of the preference for boys. "We really don't know why this is happening."

Kripa Sekhar, executive director of the South Asian Women's Centre in Toronto, said findings by Urquia and his colleagues confirmed what her organization has seen and heard from women for years.

Her organization was one of a handful consulted as part of the new research into sex selection.

"I'm not saying this happens across the board but definitely among more traditional, South Asian families there appears to be a desire to have a male child," Sekhar said.

Some of the potential reasons mothers abort female daughters can be traced to both cultural and economic reasons, she said.

Traditionally, sons take care of elderly parents and their families also receive dowries in marriages, so the birth of a boy is a joyous occasion, Sekhar said, especially for traditional families.

"I think it comes down from traditions of patriarchy," she said.​ "It's very sad … Because she's under pressure to have that male child, she actually in many ways has no choice."