Prenatal exposure to specific PM2.5 constituents and preterm birth in China: a nationwide cohort study

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Background:Prenatal exposure to fine particulate matter (PM2.5) has been linked with preterm birth (PTB) in North America and Europe. However, this association remained inconsistent and the roles of specific PM2.5 chemical constituents behind this association has never been quantified at higher ambient levels. We estimated the odd ratio (OR) for preterm delivery from prenatal exposure to PM2.5 and its chemical constituents in China.Methods:We conducted a cohort study using the China Labor and Delivery Survey data. 62,895 singleton live birth records from 25 (out of 34) provinces of mainland China between March 1st 2015 and December 31st 2016 were included. Exposures to PM2.5 total mass and 6 main constituents during the entire pregnancy and each trimester was represented by satellite-based models. Multilevel logistic regression models were used to examine the associations of PTB with PM2.5 exposure, controlling for seasonality, spatial variation and individual covariates.Results:Prenatal exposure to ambient PM2.5 was associated with increased risk of PTB, with the most significant association during the third trimester [odd ratios (OR) for an interquartile range (IQR) increase =1.09 (95% confident interval (CI): 1.01-1.18)] which became larger for infants conceived by assisted reproductive technology than ones conceived naturally. For PM2.5 composition, the strongest association per IQR was estimated for nitrate, ammonium and soil (OR=1.11–1.17), followed by black carbon and sulfate (OR=1.07-1.08). Conclusion:Constituents (e.g., ammonium and nitrate) from combustion of fossil fuel have an appreciable influence on the increased risk of PTB.