The work, by researchers from Toronto's St. Michael's Hospital, shows that the ratio of boy births to girl births is higher than average among those two communities, at least among babies born to women who've already had one child.
But the lead author of the study urged caution in interpreting the findings, saying the work doesn't prove some women are aborting female fetuses because they want to have a boy.
Another researcher who has studied the sex selection phenomenon in India said that even if the finding is true, the study suggest the number of women practising sex selection in Ontario is not huge.
"There's certainly a ratio difference that's prominent, specifically amongst Indian women ... who have had at least two prior children and in the same way among (South) Koreans who have had one prior child," said lead author Dr. Joel Ray, a researcher at St. Michael's who practises internal and obstetrical medicine.
"We don't know and we've been really careful not to speculate on the mechanism — not for fear of insulting people or miscategorizing these ratios but because mechanism is completely absent in our study."
By mechanism, Ray means he has no evidence with which to explain the higher ratio of boy births. He is working on a follow-up study, looking at data on spontaneous and elective abortions in Ontario.
That carefully anonymized data set shows the number and gender of children previously born to women undergoing terminations or who had spontaneous abortions. It is broken down by the women's ethnic background as well.
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He and his colleagues can see, for example, that immigrant women from South Korean have more boys as second children than the general population. But are those extra boys being born into families that had a girl as their first child? Or is the elevated rate of boy births among third children in families of Indian descent happening in families where the first two children were daughters?
Without knowing the birth patterns in the families, it's hard to conclude whether sex selection or something else is at play, Ray said.
"We would strongly discourage people from drawing conclusions. Those conclusions are really presumptuous and medical science and other forms of science have often drawn conclusions about a whole bunch of different things that when you complete the picture you end up realizing the conclusions were premature and wrong."
In Canada there are, on average, 105 boys born for every 100 girls.
But the study, published in this week's issue of the Canadian Medical Association Journal, shows that in women who came to Ontario from South Korea and who have already had one child, 120 boys were born for every 100 girls among second children born to those women.
For mothers who came to Canada from India, there were 111 boys for every 100 girls among second children, and 136 boys for every 100 girls among third children.
The differences in those ratios may seem big, but Dr. Prabhat Jha also warned against jumping to conclusions.
Jha, director of the Centre for Global Health Research at St. Michael's Li Ka Shing Knowledge Institute, knows about the phenomenon of sex selection. He researched the issue in India, publishing studies that quantified the loss of girl children there due to cultural preferences for boys.
In a major study published last year in the journal Lancet, he and colleagues estimated that up to 12 million girls were not born over the past three decades because of the practice of aborting female fetuses.
He called Ray's paper suggestive, but said it doesn't prove this practice is happening in Ontario. (The two are colleagues, but Jha was not an author of Ray's study.) And if it is, the practice doesn't appear to be widespread, he said.
Jha noted that over the six years of births Ray analyzed, there were nearly 32,000 children born to mothers who had immigrated to Ontario from India.
Most of those children were first children, which were born at the Canadian average rate of boys to girls. The big discrepancies in rates were seen in the third and fourth children in a family, but the total number of third and fourth children was small — about 4,100 in total.
If those children were born at the average birth ratio, 1,999 of them would have been girls, Jha said. But the actual number of girls was 1,754, about 245 fewer than would be expected. That's less than one per cent of the total births to Indian born mothers in Ontario during the period studied, Jha noted.
"The phenomenon that is occurring is occurring in quite a small number of births, if it is occurring in Ontario," he said.
The suggestion that women from some immigrant groups are selectively aborting female fetuses because they favour boy babies is a hot button topic.
Earlier this year the then acting editor of the Canadian Medical Association Journal, Dr. Rajendra Kale sparked a heated debate with an editorial he wrote suggesting sex selection is being practised by some Canadians of Asian descent.
He suggested groups that govern doctors across the country should adopt policies refusing to inform pregnant women of the sex of their fetus before 30 weeks gestation, to foil the practice.
The recommendation was strongly rejected by others, including the Society of Obstetricians and Gynecologists of Canada.