Trimester specific PM2.5 exposure and fetal growth in Ohio, 2007-2010

Background: Exposure to particulate matter, particularly with aerodynamic diameter < 2.5 mu m (PM2.5), may increase inflammation and oxidative stress in pregnant women and affect fetal growth. We examined trimester specific PM2.5 exposure levels and small for gestational age (SGA) using the statewide birth registry of Ohio from 2007 to 2010. Methods: Exposure to PM2.5 in each trimester and for each gestational week was determined using data from 57 Environmental Protection Agency network monitoring stations across the state of Ohio. We restricted the data to 224,921 singleton live births, with a gestational age of 20-42 weeks, no genetic disorders or congenital abnormalities, and who had home addresses within a 10 km radius of any PM2.5 monitoring station. We estimated odds ratios of SGA using Generalized Linear Models (GLMs) and Distributed Lag Models (DLMs), and adjustment for maternal age, race, education, parity, body mass index, insurance type, tobacco use, prenatal care initiation, birth year, season of birth, and sex of the baby. Results: Mean PM2.5 levels during the entire pregnancy were 13.03 mu g/m(3) with a standard deviation of 1.57 mu g/m(3). Covariates adjusted odds ratios and 95% confidence intervals of a 10 mu g/m(3) increase in PM2.5 levels with a 10 km buffer radius for SGA and trimesters modeled separately were 0.94 (0.88, 1.00) for the first trimester, 0.93 (0.86, 1.00) for the second trimester, 1.07 (1.00, 1.15) for the third trimester, and 0.92 (0.81, 1.06) for the entire pregnancy. When a 5 km buffer radius was used, adjusted odds ratios and 95% confidence intervals for SGA were 0.97 (0.89, 1.05) for the first trimester, 0.96 (0.88, 1.05) for the second trimester, 1.09 (1.02, 1.17) for the third trimester, and 0.99 (0.85, 1.14) for the overall pregnancy, indicating sensitivity to buffer choice. DLMs showed gestational weeks 30-35 to be a particular window of vulnerability. Conclusion: Increasing exposure to PM2.5 during the third trimester of pregnancy was associated with a small increase in risk of SGA in this population-based study. Selection of a buffer radius significantly impacted our results in the first trimester, but not in the third trimester.