Exposure to ambient PM2.5 during pregnancy and preterm birth in metropolitan areas of the state of Georgia

A number of studies has pointed to air pollution as an additional factor that could be associated with preterm birth. We assessed in this study the association between exposure to PM₂.₅ in ambient air during pregnancy and preterm birth in metropolitan areas of the state of Georgia, where the rate of preterm birth has been among the highest in the nation over the years. Birth data were obtained from the National Center for Health Statistics natality dataset. The study population consisted of 53,094 singleton live births between January 1 and December 31, 2004 in nine metropolitan counties of Georgia. Preterm birth was defined as birth, which occurs before 37 weeks of gestation. County-level daily air quality index (AQI) data obtained from the US Environmental Protection Agency (EPA) was used to estimate individual exposure levels of PM₂.₅ for each study participant based on the county of residence for the duration of the pregnancy. A multivariate logistic regression analysis was conducted to assess the association, adjusting for potential confounders. Of the infants whose mothers resided in the nine metropolitan counties of Georgia, 4543 (8.6%) were born preterm. A higher rate of preterm birth (9.8%) was observed in infants whose mothers were exposed to ambient PM₂.₅ with AQI values > 50 than the ones with AQI ≤ 50 (EPA standard for good air quality conditions). Mothers with exposure to PM₂.₅ at average AQI values greater than 50 during the entire pregnancy were at increased risk of preterm birth (odds ratio 1.15; 95% CI 1.07, 1.25), after adjusting for sex of infant, mother’s age, race/ethnicity, education, marital status, prenatal care, cigarette smoking, alcohol consumption, and season of conception. The study provides more evidence on the role of PM₂.₅ in preterm birth. Reducing exposure to ambient particulate matter, especially in urban areas, for pregnant women would be necessary to improve the health of infants.