02/11/2013 01:59 EST | Updated 02/11/2013 02:38 EST

Birth Weight In Canada: Newborns Of Immigrant Mothers Generally Larger, Study Says

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A nurse (L) at the Bunda Hospital in Jakarta attends to one of 12 babies born by C-sections on December 12, 2012. Several hospitals in Indonesia's main cities performed more Caesarians than usual with new mothers hoping a 12-12-12 birth date will bring luck to their newborns. AFP PHOTO / BAY ISMOYO (Photo credit should read BAY ISMOYO/AFP/Getty Images)

For most women, the surest way to have a healthy baby is to practice a healthy lifestyle. And based on variables such as age, sex, income, education, and ethnicity as important determinants in a population health study, it looks like Canadian women are following the right guidelines — and by extension, delivering healthy babies.

But a new study in journal Paediatric and Perinatal Epidemiology by Dr. Joel Ray, a researcher and physician at St. Michael’s Hospital, highlights some interesting facts about babies born in Ontario — specifically, that newborns born to immigrant women are bigger than those born in their mothers’ native countries, but smaller than those of Canadian-born mothers.

“Nearly all infants born to women in their native country have lower birth weights than those born to mothers who had emigrated to Canada,” Dr. Ray said in the hospital’s press release.

Baby boys weighed, on average, 115 grams more, and baby girls were 112 grams more, he added. Dr. Ray’s paper was based on the published birth weight curves recorded between 1980 and 2012 in 21 countries.

Tracking infant birth weight can help predict future outcomes for children. According to the International Journal of Epidemiology, birthweight is "used to explain variations in infant mortality and later morbidity."

Although not certain, Dr. Ray suggested these results could merely be the law of averages, since it's more likely that those who manage to migrate to Canada are leaving a higher monetary bracket and were of a higher social background in their home country.

Still, genetic predispositions, habits and adjusting to a new lifestyle (not walking as much, driving more, eating new and different foods, etc.) does influence the new immigrants' health choices, but does not necessarily make the individual any less or more healthy.

So although the infant may get additional attention from the attending staff when it is smaller, generally speaking a newborn who is lighter or heavier than average is most likely fine. But it is prudent to have a checklist which includes ethnic-specific weight charts. Misdiagnosing babies causes anxiety for the parents, and if nothing else, puts pressure on an already stretched nursing community.

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According to Statistics Canada, the year 2006 reported about 3 million immigrant women living in Canada, accounting for 20 per cent of the total female population. This mirrors the number of total immigrants, and if the trend continues, Canada could have about 11.1 million immigrants by 2031.

Dr. Ray also notes that there were exceptions in the weight results – Swedish and Israeli boys and girls were actually bigger when born in their native countries. And babies of immigrant mothers from East and South Asia are still smaller than babies born to mothers who were themselves born in Canada.

This may be explained by high levels of healthcare and social services in Sweden, and the small number of babies born to Swedish immigrants in Ontario. For Israelis, the explanation may be the higher rate of obesity among women of child-bearing age, or the possibility that Israelis don't systematically gain weight after arriving in Canada as some other immigrant groups do.

Dr. Ray said the newborns' weight differences highlight the need for newborn weight curves designed specifically for immigrants. Neither those designed for Canadian-born women nor women in their native countries accurately reflect the birth weights of children born to most immigrant groups.