Risk of Preterm Birth According to Maternal and Paternal Country of Birth: A Population-Based Study

To examine the co-contribution of maternal and paternal country of origin to preterm birth, and the differences in PTB rates between immigrants giving birth in Canada and those giving birth in their country of origin.

Using a population-based study for all of Ontario, we included 1 200 864 singleton and twin livebirths from 2002 to 2011. The risk of PTB in infants of immigrant parents from the same country was compared to those whose parents were both Canadian-born. Logistic regression analysis adjusted for maternal and paternal age, parity, marital status, income, infant sex, and twins. We also measured differences in the calculated rate of PTB among immigrants by parental country of birth minus the published PTB rate within their native country. The main outcome measures were PTB < 37 weeks, late PTB at 34 to 36 weeks, and very PTB < 32 weeks.

Compared with infants of two Canadian-born parents, those of immigrant parents from the same country had a lower risk of PTB (aOR 0.94, 95% CI 0.92 to 0.96) and late PTB (aOR 0.92, 95% CI 0.89 to 0.94) but a higher risk of very PTB (aOR 1.09, 95% CI 1.04 to 1.16). Infants of couples from Guyana, Trinidad and Tobago, the Philippines, and Jamaica were at increased risk of PTB, late PTB, and very PTB. The rate of PTB was, on average, 3% lower for newborns of immigrant parents than the published rate of PTB in their native country.

The rate of PTB is influenced by maternal and paternal country of birth. That rate is generally lower among immigrants than the rate in their native country of origin.