Newcomers to Canada should be discouraged from adopting the unhealthy diet and couch-potato lifestyle of long-term residents, say researchers who found recent immigrants had a lower risk of complications during pregnancy.

Previous studies have found that new immigrants have lower rates of chronic disease such as hypertension, heart disease and cancer — the so-called "healthy immigrant effect." The healthy effect fades after a decade, and immigrants tend to pack on pounds within a generation.

In the Results of the Recent Immigrant Pregnancy and Perinatal Long-term Evaluation Study, or RIPPLES, study appearing in Tuesday's issue of the Canadian Medical Association Journal, Dr. Joel Ray of St. Michael’s Hospital in Toronto and his colleagues at the Institute for Clinical Evaluative Sciences found the healthy immigrant effect also extends to a pregnancy complication called maternal placental syndrome.

The syndrome is defined as a diagnosis of pre-eclampsia (a sudden increase in a woman's blood pressure in late pregnancy), eclampsia (a serious form of poisoning in pregnancy), premature separation of the placenta from the uterus, or a sudden blockage of the blood supply to the placenta.

The risk of the syndrome was lowest among women who immigrated within three months of delivering, and highest for those who had lived in Ontario for five years or more before giving birth, the team found.

"A reasonable public health recommendation based on the findings from RIPPLES and other studies is that we should aim to preserve the apparent healthier state of new immigrant women through policies designed to discourage the adoption of adverse lifestyle choices," the study's authors concluded.

"For long-term immigrants and native-born residents, the goal should be to improve their health status."

For all Canadians, the approach includes promoting nutritious eating before pregnancy to prevent obesity, as well as higher physical activity from childhood through early adulthood and limits on calorie intake, they said.

Factors that can harm the health of the placenta and fetus, such as high blood pressure, obesity and smoking, also increased the longer immigrants lived in the province, the researchers found.

Currently, immigrants are carefully screened to ensure they are in good health, and may be deemed inadmissible to Canada if they have end-stage organ disease, certain cancers, infectious diseases or need long-term nursing care, the study's authors said.

The study's findings support expanding the scope and focus of immigrant screening away from exclusion for disease and toward sustaining and improving the health of immigrants, such as addressing their reproductive health needs, Dr. Brian Gushulak of Migration Health Consultants said in a journal commentary accompanying the study.

Describing and quantifying the healthy immigrant effect also helps to reduce the wrong impression that immigrants frequently need or use excessive amounts of medical services, he added.

"Finally, and perhaps most importantly, these studies provide information that will generate better tools and interventions to maintain the health of those representing the largest component of Canada's population growth," Gushulak wrote.