Quantifying the association between pregnancy exposure to biomass-attributable PM2.5 and the risk of preterm birth and stillbirth A case-control study in Sydney, Australia for 2010–2020

Abstract

Biomass combustion, including wildfires and residential wood burning, is a significant source of particulate matter (PM2.5) in Australia, with potentially distinct health effects due to its unique chemical composition. This study aimed to quantify the association between exposure to ambient biomass-attributable PM2.5 and the risk of preterm birth and stillbirth across pregnancy windows in Sydney, Australia, from 2010 to 2020. We conducted case–control studies nested within a cohort of 578,391 singleton pregnancies, including 29,954 preterm births and 2,928 stillbirths. Controls were randomly selected using risk-set sampling. Daily all-source PM2.5 estimates at a 5 km resolution were obtained from a previous study. Days exceeding the 95th percentile of all-source PM2.5 at statistical area level 4 without significant dust storm pollution were classified as biomass-affected days. For these days, biomass-attributable PM2.5 was estimated using the remainder component from a seasonal trend decomposition, with the seasonal and trend components representing nonbiomass-attributable PM2.5. Conditional logistic regressions were used to analyze associations between biomass-attributable PM2.5 exposure and outcomes, adjusting for area-level socioeconomic factors, temperature, humidity, and temporal and seasonal trends. The odds ratio for preterm birth per interquartile range increase in biomass-attributable PM2.5 was 1.002 (95% CI = 0.997, 1.007) for the entire pregnancy average exposure, with similar null results across trimesters. For stillbirth, the odds ratio was 1.002 (95% CI = 0.985, 1.019) for the entire pregnancy average exposure, with comparable null findings across trimesters. These results suggest that in Sydney, biomass-attributable PM2.5 exposure during pregnancy may not increase the risk of preterm births or stillbirths.