Effects of Prenatal Exposure to PM^2.5Chemical Components on Adverse Birth Outcomes and Under-5 Mortality in South Korea

Background: Exposure to fine particulate matter (PM2.5) during pregnancy has been associated with adverse birth outcomes. However, limited evidence exists on the effects of specific PM2.5 components. We investigated the association of prenatal exposure to PM2.5 and its components with birth outcomes and mortality at age <5 years in four metropolitan cities in South Korea. Methods: We obtained data from Statistic Korea linking birth records for 2013-2015 to death records under age 5 years. Data for PM2.5 and 10 of its components were collected from four monitoring stations. We calculated exposures during pregnancy and each trimester for a total of 324,566 births. We used logistic regression to estimate the associations between exposure and risk of preterm birth (PTB) (<37 weeks), low birth weight (<2.5 kg), small for gestational age (birth weight <10th percentile for the same gestational age), and under-5 mortality. Results: An interquartile range (8.7 g/m3) increase in exposure to PM2.5 during the entire pregnancy was associated with increased odds of PTB (odds ratio [OR] = 1.17; 95% confidence interval [CI] = 1.11, 1.23). We observed no association with low birth weight, small for gestational age, or under-5 mortality for the entire pregnancy exposure. Elemental carbon and secondary inorganic aerosols showed higher effect estimates for PTB than did other components. Conclusions: In urban populations of South Korea, exposure to PM2.5 during pregnancy was associated with an increased risk of PTB. Different components showed varying associations with adverse birth outcomes.