Prevalence and National Trends in Prenatal Wildfire Smoke Exposure Among Live Births

Wildfire smoke is an increasing source of pollution in the United States and can affect communities far from active fires. The developing fetus is vulnerable to prenatal smoke exposure, yet existing evidence is focused on a few western states. This population-based retrospective cohort study documents national patterns and trends in prenatal wildfire smoke exposure across geographic and sociodemographic groups.

Satellite-based wildfire smoke plumes were combined with restricted-use vital statistics microdata for 34,440,915 live births in the contiguous United States from 2012-2020. Prenatal exposure was measured as the number of days during gestation with medium or heavy wildfire smoke in the mother's county of residence. Changes in median smoke-days, the share of infants prenatally exposed to ≥7 smoke-days, and wildfire-attributed PM_2.5 on smoke-days overall and by maternal and county characteristics were examined. Statistical significance was assessed using t-tests and quantile regression. Analysis was performed from March to November 2024.

25.5 million infants (74.2%) had prenatal smoke exposure. 4.3 million (22.7%) births had at least 7 days of exposure in 2016-2020, a significant increase from 2012-2015 (p<0.001). Median exposure significantly increased from 0.6 days in 2012-2015 to 2.0 days in 2016-2020 (p<0.001). Non-Hispanic American Indian/Alaska Native infants, infants living in rural counties, and states in the Upper and Western Midwest and Rocky Mountains faced the highest prenatal exposures.

Prenatal wildfire smoke exposure is widespread, increasing, and not confined to regions near active fires. These findings highlight a growing national public health concern and underscore the need for preparedness, targeted prevention, and risk-appropriate care across communities.