Prenatal exposure to wildfire fine particulate matter and fetal growth outcomes in the United States: Findings from the ECHO Cohort.

BACKGROUND

Increasing exposure to wildfire fine particulate matter (PM2.5) may pose unique risks to fetal development. We assessed associations between prenatal wildfire PM2.5 exposure and fetal growth outcomes, including birth weight at term, birth weight for gestational age z-scores, small for gestational age, and large for gestational age in the U.S. Environmental Influences on Child Health Outcomes Cohort.

METHODS

The study included 20,034 births (2006-2020) from 30 cohort sites nationwide. We assigned daily wildfire PM2.5 at census-tract resolution and summarized average concentrations and the number of smoke days exceeding multiple intensity thresholds across pregnancy. We used covariate-adjusted mixed-effects models to estimate overall associations and distributed lag models and trimester-specific analyses to evaluate critical exposure windows across gestation, and we examined potential effect modification by US region, fetal sex, maternal race, and neighborhood poverty.

RESULTS

Pregnancy wildfire exposure metrics, including mean prenatal PM2.5 and the number of smoke days, were not associated with study outcomes. Distributed lag and trimester-specific models did not show consistent sensitive windows of exposure associated with birth weight at term, birth weight for gestational age z-scores, or small for gestational age. A positive association was observed between higher early-pregnancy wildfire exposure and large for gestational age (odds ratio = 1.015 per smoke day, 95% confidence interval: 1.001, 1.029), though effect estimates were small in magnitude. No consistent effect modification was identified.

CONCLUSION

In this nationwide cohort, wildfire PM2.5 showed limited associations with fetal growth outcomes.