It is rarely openly discussed and difficult to prove, but new research suggests that some couples in Canada are practising prenatal sex selection, aborting female fetuses out of a preference for male children.

Two related studies, published on Monday in CMAJ (Canadian Medical Association Journal), found a higher-than-expected ratio of boys to girls born to immigrants from India over the past two decades, which researchers linked to preceding abortions. This gender imbalance was particularly striking among families that already had two daughters.

"This suggests that many of the abortions may have involved female fetuses. And that's why the sex ratio at the third birth is distorted," said Marcelo Urquia, a researcher at St. Michael's Hospital in Toronto who led both studies.

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"I think the most important implication is that some immigrant groups put more value on the life of sons than daughters," he added. "If a son preference exists at this point in life, this raises the question of whether females in some immigrant communities are also at a disadvantage at other life stages – for example, in infancy, childhood, adolescence and adulthood."

The suggestion that certain immigrant groups in Canada use abortion to select the sex of their children has long been a contentious issue. Politicians and activists have argued for legal limits on abortion to deter sex-selection. And a controversial CMAJ editorial in 2012 recommended banning the disclosure of the sex of a fetus until 30 weeks, when abortions are performed only in rare circumstances. But such measures are difficult to enforce and, some argue, unjustifiably sweeping, while others note that identifying and targeting specific groups for practising sex selection is discriminatory.

One of the studies published Monday examined national data for 5.9 million births, between 1990 and 2011, to Canadian-born women and 177,990 births to women who had been born in India.

Among Canadian-born mothers, the researchers found that about 105 boys were born for every 100 girls, consistent with the natural odds of 103 to 107 boys for every 100 girls.

By contrast, among Indian-born mothers, the proportion of males increased with the number of children born. By the third birth, 138 boys were born to Indian-born mothers for every 100 girls, and by the fourth birth, 166 boys were born to every 100 girls.

The researchers estimated that over the past two decades, there have been at least 4,472 "missing girls" – that is, female fetuses not born to Indian immigrants in Canada, primarily in families where both parents are from India.

Although a preference for sons is recognized among other groups, the authors noted that they zeroed in on immigrants from India because of its high documented male-to-female ratios, and because the country contributes a large number of immigrants who give birth in Canada.

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The second study examined records for more than 1.2 million babies born in Ontario between 1993 and 2012 to women who had up to three children. Within the province, researchers found women from India who already had two daughters gave birth to 196 boys for every 100 girls. If an Indian-born mother with two daughters received an abortion before their third child, the ratio jumped to 326 boys for every 100 girls, and 409 boys for every 100 girls if the mother had multiple abortions.

While couples may allow for a daughter as their first or second child, the skewed sex ratios likely appear in subsequent births as families approach their limit in size, Urquia explains. "Then this issue of having a son becomes more important for some families."

The second study also indicated a slight imbalance in boys born to Chinese immigrants, but Urquia said the researchers did not find this was linked to abortions.

In an accompanying commentary in CMAJ, authors Abdool Yasseen and Thierry Lacaze-Masmonteil of the Children's Hospital of Eastern Ontario in Ottawa said the results of these studies offer "strong evidence" of the use of abortion for prenatal sex selection, and called for discussion aimed at examining and developing public-health policies to curb the practice.

"We need to sort of approach that with tact because you don't want to single out a particular ethnic group, but you do want to intervene if something discriminatory is happening," said Yasseen, a clinical investigator.

Although sex selection is banned in Canada when it comes to assisted reproductive treatment, the country has no law on abortion, including its use for sex selection. While professional bodies, such as the Society for Obstetricians and Gyneologists of Canada, have policies against sex-selective abortions and against the use of medical testing solely for identifying a fetus's sex, some parents and doctors object, arguing that parents have the right to know, Yasseen and Lacaze-Masmonteil wrote.

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While studies such as the ones published Monday may show patterns that indicate sex selection is likely occurring, individual parents do not often openly acknowledge using abortion for that purpose.

Shree Mulay, associate dean and professor of community health and humanities at Memorial University of Newfoundland, said she has heard accounts from social workers who have had women ask for the sex of their fetuses, only to later learn that they terminated the pregnancy after finding out.

Mulay, who specializes in immigrant women's health, said women are not necessarily the ones seeking sex-selective abortion, but may feel pressured to do so by their families.

One reason males may be preferred, she said, is that, "according to the Indian family customs, the male of the family is supposed to … take responsibility for looking after the elderly parents."

Even though this does not always happen in practice today, Mulay, a founding member of Montreal's South Asian Women's Community Centre, said some people tend to adhere to traditions, even more rigidly than they might otherwise in their country of origin, as they settle in a new place.

"But traditions have to be challenged," she said, adding that to be effective, efforts to change attitudes that favour sons over daughters must come from within the immigrant groups themselves.

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At Mosaic, an immigrant and refugee settlement organization based in Vancouver, Ninu Kang said she already sees signs of this happening among various immigrant groups. The preference for male children decreases as families recognize females have greater opportunities and are more empowered in Canadian society, she said.

For example, she said families in Canada increasingly celebrate the Punjabi festival Lohri, which is traditionally held in honour of the birth of a boy, for their daughters as well.

Amrita Mishra, project director of the Indo-Canadian Women's Association in Edmonton, said the key issue is that the existing legal loopholes allow anyone to use abortion for infant sex selection.

"I see Canada as enabling as such practices. And I refuse to have this turn into an Indian issue that's been imported like vegetables or fruit into Canada," Mishra said, noting that a law against sex-selective abortion would send a powerful message to anyone considering the practice.

"When one says Indians or Chinese, Koreans or Philippines have brought this problem to a country, we really need to take a good solid look at ourselves and ask ourselves what are the laws in this country that allow this to happen?" she said.