Prenatal PM2.5 exposure and the risk of adverse births outcomes: Results from Project ELEFANT

Background: Studies investigating the impact of fine particulate matter (PM<inf>2.5</inf>) exposure during pregnancy upon adverse birth outcomes have primarily been performed in Western nations with low ambient PM<inf>2.5</inf> levels. We examined associations between high levels of PM<inf>2.5</inf> exposure during pregnancy and risk of adverse birth outcomes by timing and level of exposure in a Chinese population. Methods: We analysed data from 10,738 live births within the Project ELEFANT study based in Tianjin, China. Personal mean daily PM<inf>2.5</inf> exposures were estimated using data from 25 local monitoring sites across the city, used to compute the days exceeding 50, 100, 150, 200 and 250 μg/m³. Relative risk of pre-term birth (<37 weeks) and low birthweight (<2500 g) were estimated by generalized additive distributed lag models, adjusted for maternal age, sex, region, paternal smoking, parity, maternal occupation, season, temperature and dew point. Results: A dose-response was exhibited for PM<inf>2.5</inf> exposure and relative risk (RR) of adverse birth outcomes, with exposure in the second and third trimesters of pregnancy associated with greatest risk of adverse birth outcomes. The RRs of pre-term birth with exposures of >50, >150 and > 250 μg/m³ PM<inf>2.5</inf> in the third trimester were 1.09 (95%CI: 1.03–1.16), 1.30 (1.09–1.54) and 2.73 (2.03–3.66) respectively. For low birthweight, exposures of >50, >150 and > 250 μg/m³ PM<inf>2.5</inf> in the third trimester were associated with RRs of 0.99 (0.88–1.11), 1.37 (1.04–1.81) and 3.03 (1.75–5.23) respectively. Conclusions: Exposure to high levels of PM<inf>2.5</inf> from the second trimester onwards was most strongly associated with increased risk of pre-term birth and low birthweight, with a dose-response relationship. Our data demonstrates the need to account for both level and timing of exposure in analysis of PM<inf>2.5</inf>-associated birth outcomes.