Perinatal health among foreign versus native-born mothers in Canada: variations across outcomes and cohorts.

BACKGROUND: To examine perinatal health differences between foreign-born and native-born mothers in Canada across multiple outcomes and two cohorts 10 years apart. METHODS: Using 94 896 and 131 271 births in the 1996 and 2006 Canadian Census-Birth Cohort, respectively, we estimated risk ratios and risk differences of preterm birth (PTB), small-for-gestational age (SGA), large-for-gestational age (LGA), stillbirth and infant mortality between foreign-born and Canadian-born mothers. RESULTS: In the 1996 cohort, we observed no important differences in adverse outcomes between foreign-born and native-born mothers. In the 2006 cohort, however, foreign-born mothers had lower risks of PTB, LGA, stillbirth, and infant mortality and a higher risk of SGA on both the relative and absolute scales. Lowered risk of PTB among foreign-born mothers in the 2006 cohort was also observed within Caucasian, East Asian, Southeast Asian and South Asian mothers. Favourable outcomes associated with foreign-born status in the 2006 cohort were negatively graded by duration of residence in Canada among immigrant mothers. CONCLUSIONS: Differences in perinatal health by maternal foreign-born status varied across cohorts and a more pronounced 'healthy migrant' effect was observed among more recent migrants. The native-born mothers' perinatal health over time and a more restrictive/selective immigration policy in recent years would explain our results.