Researchers from the University of Maryland, College Park published a study in Frontiers in Environmental Health on Thursday regarding prenatal exposure to wildfire smoke. The analysis indicates that increasing wildfire activity is systematically offsetting prenatal air quality gains from reducing emissions from vehicles, refineries, factories and other human sources.

The study analyzed air pollution data from the Environmental Protection Agency and live birth records for nearly 65 million babies born in the contiguous United States between 2003 and 2019. This dataset covered 2,842 counties in 48 states, providing a broad view of exposure trends across the country during this period.

Average daily prenatal exposure to air pollution from human sources dropped by 37 percent between 2003 and 2019. Daily prenatal PM2.5 exposure from all sources decreased by approximately 34 percent on average during the same timeframe, reflecting broader improvements in ambient air quality.

Despite these reductions, the contribution of wildfire smoke to prenatal PM2.5 exposure more than doubled between 2003 and 2019, rising from approximately 3.7 percent to 8.2 percent. By 2019, approximately 65 percent of prenatal PM2.5 exceedance days were attributed to wildfire smoke.

Regional variations showed distinct increases in wildfire contributions. In Western states, wildfire contributions to PM2.5 pollution increased from approximately 3.7 percent to 9.7 percent between 2003 and 2019.

Prenatal exposure to wildfire smoke significantly increases the likelihood of preterm birth and low birth weight. Low-income, rural, and Indigenous populations bore a disproportionate burden of wildfire-related poor air quality during the study period.

"We were looking at infants that were born and what their exposure was like during the prenatal period," Michel Boudreaux, associate professor of health policy and management, said. "What that tells me is that the next frontier is how do we help people manage exposure to wildfire smoke, which is a different kind of exposure than ambient pollution from other sources."

Menglu Liang, assistant clinical professor, emphasized the long-term implications of these exposures. "These outcomes matter well beyond the delivery room and harms experienced before birth can echo for decades," Liang said. She added that the benefits of previous regulatory efforts remain critical despite the new challenges posed by wildfires.

"Those gains have genuinely protected pregnant people and unborn babies, and without them exposures today would be considerably worse," she said. "What our findings show is that wildfire smoke is offsetting a growing share of these hard-won improvements."

The study identified specific demographic disparities in exposure levels. "Wildfire pollution burdens were highest for low-income, rural, American Indian and Alaska Native communities, and areas with shortages of maternity care services," she said. Communities disproportionately affected by wildfire smoke often have the least access to neonatal care.

She described the methodological shift as essential for equitable public health planning. "The central contribution of this work is a shift in perspective. Prior research has mapped very well where wildfire smoke occurs, but public health resources are allocated to populations, not to acres," she said.

"With these results, we can begin to answer who is exposed and where they live. We need this information to target interventions and allocate resources fairly."

Ilona Jaspers, professor of pediatrics, commented on the study's alignment with existing knowledge. "What this study does do well is confirm and expand the well-established finding that ambient PM2.5 in the United States is increasingly wildfire-dominated, offsetting Clean Air Act gains, but applies a birth-weighted lens to it," Jaspers said.

The study did not account for individual behaviors such as time spent outdoors, use of N95 masks, or home air-filtration systems. It also did not track whether individuals moved across counties or regions during pregnancy, which could influence exposure estimates.

Why It Matters

Rising wildfire smoke is systematically offsetting prenatal air quality gains achieved through decades of emissions reductions, threatening to reverse progress made under the Clean Air Act. This shift disproportionately impacts low-income, rural, and Indigenous communities that often lack access to neonatal care, linking environmental changes directly to increased risks of preterm birth and low birth weight. The findings indicate that public health strategies must evolve from regulating stationary sources to managing wildfire exposure to protect future generations.