Long-term ambient sulfur dioxide exposure during gestation and preterm birth in North Carolina, 2003-2015

Coal-fired power plants are major contributors of ambient sulfur dioxide (SO2) air pollution. Epidemiological literature suggests an adverse association between SO2 exposure during gestation and preterm birth (PTB; <37 weeks completed gestation). PTB is strongly associated with infant mortality and increased risk for later life morbidities. We investigated associations between SO2 and PTB in North Carolina and evaluated whether the associations were modified by race/ethnicity. We assembled a retrospective, administrative cohort of singleton births in North Carolina from 2003-2015. We used US EPA EQUATES data to assign long-term SO2 gestational exposures to eligible births for the entire pregnancy and by trimester. We used multivariable generalized linear regression to estimate risk differences (RD (95%CI)) per 1-ppb increase in SO2, adjusted for gestational parent education, Medicaid status, marital status, and season of conception. Multi-pollutant models were additionally adjusted for other criteria air co-pollutants (O3, PM2.5, NO2). The median SO2 (24-hour average) across exposure windows was ∼1.5 (IQR: 1.8) ppb. The overall baseline risk for PTB was 8,756 per 100,000 live births. When stratified by race/ethnicity, the baseline risk for PTB was 12215, 7824, and 7187 per 100,000 live births among non-Hispanic Black, non-Hispanic white, and Hispanic births, respectively. RDs per 1-ppb increase in SO2 averaged across the entire pregnancy were 317.0 (95%CI: 279.4, 354.5) and 568.2 (95%CI: 500.3, 636.1) per 100,000 live births for single- and multi-pollutant models, respectively. For the PTB multi-pollutant models, we observed similar RDs for non-Hispanic Black participants (669.6 [95%CI: 573.9, 765.2]) and non-Hispanic white participants (635.4 [95%CI: 557.2, 713.6]) with smaller RDs for Hispanic participants (336.8 [95%CI: 241.3, 432.2]). The results for our adjusted single- and multi-pollutant models showed adverse associations between SO2 and PTB, with some evidence of effect measure modification by race/ethnicity within subcategories of PTB.