Maternal exposure to gaseous ambient air pollutants increases the risk of preterm birth in the Pearl River Delta, China 2014–2017

Abstract The association between maternal exposure to gaseous air pollutants and preterm birth is still unclear. We assessed the effects of ambient sulfur dioxide (SO 2 ), nitrogen dioxide (NO 2 ), and carbon monoxide (CO) on preterm birth based on a large cohort of live births in China. Data for a total of 1,098,600 singleton live births in nine subtropical cities in the Pearl River Delta, South China from January 1, 2014 through October 31, 2017 were collected. Information on date of birth, birth weight, fetal outcome, infant sex, gestational age, parity, maternal age, maternal ethnicity, maternal cigarette smoking state and mother's residential address was collected. Odds ratios (ORs) and corresponding 95% confidence intervals (CIs) for an interquartile range (IQR) increment in concentrations of air pollutants were estimated to examine the associations between month- and trimester-specific concentrations of the pollutants and preterm birth based on generalized estimating equation. Population-attributable risk was also calculated to estimate the number of excess preterm births associated with air pollution exposure. Of all the births included, 54,521 (4.96%) were preterm. In full adjusted model, elevated risk of preterm birth was associated with an IQR increment in maternal exposure to SO 2 (OR = 1.287, 95% CI, 1.204–1.375), especially during the first trimester of pregnancy (OR = 1.136, 95% CI, 1.097–1.177). Similarly, elevated risk of preterm birth linked to CO exposure during the first trimester of pregnancy (OR = 1.085, 95% CI, 1.056–1.115) was found. Additionally, increased odds of preterm birth associated with NO 2 exposure during the third trimester of pregnancy (OR = 1.092, 95% CI, 1.043–1.143) were seen. The magnitude of association between very preterm birth and air pollution was larger than that for preterm birth. The associations were modified by maternal age, mother parity, infant sex and birth season of infant. Our study suggests maternal exposure to outdoor gaseous air pollutants increases risk of preterm birth.