Impact of Wildland Fire Smoke PM_2.5 on Birth Weight in California

The increase in the frequency, duration, and intensity of wildland fires is a significant source of air pollution that can impact perinatal outcomes. This study assessed associations between wildfire fine particulate matter <2.5 μm (PM_2.5) and adverse birth weight outcomes among singleton term births in California for 2007-2018. Exposure was assessed using bias-corrected Community Multiscale Air Quality Model, linked to residence at delivery. Logistic and linear regression models estimated associations between average daily wildfire PM_2.5 and birth weight outcomes, adjusting for individual-level sociodemographic covariates and seasonality. We conducted race/ethnicity-stratified analyses to assess whether the influence of wildfire PM_2.5 differed among racially marginalized populations. In a sample of 4,537,418 term births, a 1 μg/m³ increase in wildfire PM_2.5 during pregnancy was associated with increased odds of large for gestational age and an increase in birth weight, as well as moderately decreased odds of low birth weight and small for gestational age. These associations were more pronounced among Hispanic individuals and those in the Other race category. Conversely, among American Indian and Alaska Native births, exposure to wildfire PM_2.5 was associated with decreased odds of large for gestational age. Results underscore the importance of understanding how wildfire PM_2.5 impacts fetal growth, especially among marginalized groups.