Women who immigrate to Ontario have babies who are bigger than those born in their native countries, new research has shown.
But the babies of immigrant mothers from East and South Asia are still smaller than babies born to mothers who were themselves born in Canada.
The typical male born to an immigrant mother in Ontario weighs 115 grams more than babies in her native country, said Dr. Joel Ray, a researcher and physician at St. Michael's Hospital. The typical female weighs 112 grams more than babies in her mother's native country, he said.
His findings appear online in the journal Paediatric and Perinatal Epidemiology.
"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.
Dr. Ray said he was not sure why the weight differences exist. He said it may be a byproduct of an immigration policy that selects more robust and well-off immigrants. Or it may be that immigrants ingest more calories and exercise less than in their native countries, so both they and their babies are bigger.
There were some exceptions – notably Swedish and Israeli boys and girls, all of who were bigger when born in their native countries. Dr. Ray said this may be explained by high levels of health care 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 and-or the possibility Israelis do no systematically gain weight after arriving in Canada as some other immigrants do.
The biggest weight differences tended to be between babies born in Ontario and those born in poorer, less developed countries.
Dr. Ray said the weight differences highlight the need for newborn weight curves designed specifically for immigrants. Neither those designed for Canadian-born women or women in their native countries accurately reflect the birth weights of children born to most immigrant groups.
Birth weight curves are graphs used to plot how one baby's weight compares to others of the same age. They are important for identifying babies who are both small and large for their gestational age. Babies who are small for their gestational age are at risk of developmental issues. Those who are large may need to be delivered early or by way of Cesarean section.
In 2006, there were about 3 million immigrant women living in Canada, accounting for 20 per cent of the total female population.
Dr. Ray's paper was based on a systematic review of all birth weight curves published between 1980 and 2012 in 21 countries accounting for 13.3 million single male births and 12.9 single female births at 40 weeks gestation.