Concomitant preterm birth and severe small-for-gestational age birth weight among infants of immigrant mothers in Ontario originating from the Philippines and East Asia: a population-based study

Objectives Women from the Philippines form one of the largest immigrant groups to North America. Their newborns experience higher rates of preterm birth (PTB), and separately, small-for-gestational age (SGA) birth weight, compared with other East Asians. It is not known if Filipino women are at elevated risk of concomitant PTB and severe SGA (PTB-SGA), a pathological state likely reflective of placental dysfunction and neonatal morbidity. Methods We conducted a population-based study of all singleton or twin live births in Ontario, from 2002 to 2011, among immigrant mothers from the Philippines (n=27 946), Vietnam (n=15 297), Hong Kong (n=5618), South Korea (n=5148) and China (n=42 517). We used modified Poisson regression to generate relative risks (RR) of PTB-SGA, defined as a birth < 37 weeks' gestation and a birth weight < 5th percentile. RRs were adjusted for maternal age, parity, marital status, income quintile, infant sex and twin births. Results Relative to mothers from China (2.3 per 1000), the rate of PTB-SGA was significantly higher among infants of mothers from the Philippines (6.5 per 1000; RR 2.91, 95% CI 2.27 to 3.73), and those from Vietnam (3.7 per 1000; RR 1.68, 95% CI 1.21 to 2.34). The RR of PTB-SGA was not higher for infants of mothers from Hong Kong or South Korea. Interpretation Among infants born to immigrant women from five East Asian birthplaces, the risk of PTB-SGA was highest among those from the Philippines. These women and their fetuses may require additional monitoring and interventions.