Fine Particulate Matter and Risk for Preterm Birth in Connecticut in 2000–2006

Abstract

Preterm birth occurs in more than 12% of births in the United States. Its etiology is multifactorial, with exposure to ambient air pollution a suggested risk factor. Fine particulate matter with aerodynamic diameter of less than 2.5 μm (PM2.5) can elicit biologic responses. This longitudinal study was performed to test the hypothesis that a woman is at more risk for preterm delivery when she has elevated exposure to ambient PM2.5 during pregnancy. The study assessed women’s exposure to ambient airborne PM2.5 and preterm birth (PTB) across successive pregnancies in Connecticut (2000–2006). From 271,204 singleton live births, the study population comprised 61,688 neonates born to 29,175 women. Daily (24-hour) mean PM2.5 measurements, taken every third day, were obtained from an Environmental Protection Agency PM2.5 monitor within 40 km of each woman’s residence at the time of birth. Daily measurements were also obtained for CO, NO2, and SO2. Mean exposures were computed for each week of gestation and used to compute exposure for each trimester and the whole pregnancy. Adjustment was made for the mean number of cigarettes smoked per day, maternal age, and parity. The prevalence rates of PTB for black, Hispanic, and white women were 9.4%, 7.0%, and 5.3%, respectively. Most variation (92.9%) in daily measurements of PM2.5 was due to temporal factors rather than spatial/site factors (7.1%). Because a pregnancy spans multiple seasons, 78.5% of the variation in mean pregnancy exposure to PM2.5 was explained by site and 21.5% was explained by timing of pregnancy. Timing of pregnancy explained 53.5%, 52.5%, and 63.3% of the variation in first-, second-, and third-trimester PM2.5 exposures, respectively. The median exposure to PM2.5 in pregnancy was 12.38 μg/m3. The mean whole-pregnancy exposures for the first and second births to each woman were 12.69 μg/m3 and 12.36 μg/m3, respectively (P < 0.001). The odds of PTB increased by a factor of 1.10 (95% confidence interval [CI], 1.03–1.17) per interquartile range (IQR) increase in first-trimester PM2.5. The odds of PTB decreased by a factor of 0.93 (95% CI, 0.87–0.99) per IQR in second-trimester PM2.5. Adjusted ORs per IQR (2.33 μg/m3) increase in PM2.5 in the first trimester, second trimester, third trimester, and entire pregnancy were 1.07 (95% CI, 1.00–1.15), 0.96(95% CI, 0.90–1.03), 1.03 (95% CI, 0.97–1.08), and 1.13 (95% CI, 1.01–1.28), respectively. Among Hispanic women, the OR per IQR increase in whole-pregnancy exposure was 1.31 (95% CI, 1.00–1.73). An adverse association with PTB for elevated maternal exposure to PM2.5 was found in the first trimester of pregnancy. Weak evidence was seen for a 7% increase in risk for PTB among all women, and strong evidence was seen for an 18% increase in risk among Hispanic parturients.