Objective

Test the hypothesis that exposure to fine particles in the air (PM2.5) is associated with increased risk of preterm birth (PTB).

Study Design

Geo-spatial population-based cohort study using live birth records from Ohio(2007-2010) linked to average daily measures of PM2.5, recorded by 57 EPA network monitoring stations across the state. Geographic coordinates of the home residence for births were linked to the nearest monitoring station using ArcGIS. Association between PTB and high PM2.5 levels (above the EPA annual standard of 15ug/m3) was estimated using GEE, with adjustment for age, race, education, parity, insurance, tobacco, birth season and year, and baby gender. An exchangeable correlation matrix for the monitor stations was used in the models. Analyses limited to singleton births at 20-42 wks with no known chromosome abnormality occurring within 10km of a monitor station.

Results

The frequency of PTB was 8.5% and small for gestational age (SGA, BW<2500 gm) was 6.9% in the study cohort, n=224,921. High PM2.5 exposure >EPA recommended max occurred frequently during the study period, with 24,662 women (11%) having high exposure in all three trimesters. Pregnancies with high PM2.5 exposure through pregnancy had increased PTB risk even after adjustment for coexisting risk factors, aOR1.15(1.06-1.25). Assessed per trimester, high 3rd trimester PM2.5 had the highest PTB risk, aOR1.25(1.18-1.33). High exposure in 3rd trimester and through pregnancy also increased SGA risk, aOR1.16(1.09-1.24) and 1.24(1.16-1.32) respectively.

Conclusion

Exposure to high levels of fine particulate air pollution, PM2.5, in pregnancy is associated with increased risk of PTB and SGA. Although the risk increase associated with high PM2.5 levels is modest, the potential impact on overall PTB rates is robust as all pregnant women are potentially at risk. This may in part contribute to the higher preterm birth rates in Ohio compared to other states in the US, especially in urban areas.