Health Advantages and Disparities in Preterm Birth Among Immigrants Despite Disparate Sociodemographic, Behavioral, and Maternal Risk Factors in San Diego, California.

Introduction: Reproductive health advantages have been reported among selected immigrants, but few studies have included new immigrants and refugees, nor simultaneously adjusted for socioeconomic, behavioral, and medical disparities.

Methods: We examined the risk of preterm birth (PTB, < 37 weeks' gestation) among singleton live births in San Diego County from 2007 to 2012. Multivariable regression was used to compare PTB (1) by nativity within racial/ethnic groups and (2) among immigrants compared to United States (US) born Whites, while adjusting for sociodemographic, behavioral, reproductive and medical variables.

Results: Among 230,878 singleton live births, overall PTB prevalence was highest among parturient women who were US-born Blacks (10.9%), Philippine (10.8%) and US-born Filipinas (10.7%), and US-born Asians (8.6%) despite differences in socioeconomic and maternal risk factors, and lowest among Somali (5.5%) migrants. Blacks born in Somalia or outside of the US, had significantly lower overall PTB prevalence compared to US-born Blacks (5.5% vs 7.6% vs 10.9%). Compared to US-born Whites, spontaneous PTB risk was significantly lower among Somali migrants (4.8% vs 3.7%, adjusted relative risk, aRR 0.7 [95% Confidence Intervals 0.5-0.9]), but higher among Philippine migrants (4.8% vs 7.7%, aRR 1.4 [1.3-1.6]). The strongest risk factor for overall PTB among nulliparous US-born Blacks was preexisting diabetes (aRR 3.81 [2.05-7.08]), and preexisting hypertension among Filipinas (aRR: 3.27 [2.36-4.54] and US-born Asians (aRR: 3.64 [1.61-8.24]).

Conclusion: Black migrants had lower PTB prevalence compared to US-born Blacks, but this immigrant advantage was not observed in other racial/ethnic groups. Compared to US-born Whites, Somali migrants had significantly lower risk of spontaneous PTB while Filipinas had elevated risk.