Associations of PM_2.5 and PAHs from wildland fires with pregnancy outcomes: evidence based on high-resolution...

Wildfire threats are increasing dramatically in the United States and compromising decades of progress in air quality improvements. However, research on wildfire PM_2.5 and preterm birth (PTB) remains limited. No studies have examined wildfire-emitted polycyclic aromatic hydrocarbons (PAHs), a potential driver of wildfire PM_2.5 toxicity, or specifically investigated preterm premature rupture of membranes (PPROM), a leading cause of PTB. We used statewide birth certificate data in California and estimated hourly concentrations of PM_2.5 and particulate-phase PAHs from wildland fires at a 1 km resolution in 2017 and 2018, based on a two-stage machine learning model integrating the Community Multiscale Air Quality model outputs. We applied the generalized linear mixed model to examine the associations of wildfire PM_2.5 and PAH exposures during pregnancy with PTB and PPROM. We examined the effect modification by maternal characteristics and other environmental exposures and calculated the population-attributable fractions of PTB. We observed positive associations of maternal exposures to wildfire PM_2.5 and PAHs with PTB and PPROM among 627,494 births, particularly during the second trimester. Every interquartile range increase in wildfire PM_2.5 was associated with a 13% (95% CI: 12%, 14%) higher risk of PTB. Race/ethnicity, pre-pregnancy body mass index, season of conception, non-wildfire PM_2.5 exposure, and temperature exposure were important effect modifiers. Approximately 6.96% of PTB cases can be attributed to higher exposure to wildfire PM_2.5 during pregnancy. These findings highlight the need for targeted public health interventions to reduce wildfire smoke exposure during pregnancy, especially among vulnerable populations.