A new study examining pollution levels over a 16-year span has found that increasing wildfire smoke air pollution is offsetting previous declines in pollution from vehicles and industry. This shift could contribute to negative outcomes for pregnant women and babies, including preterm births and low birth weight.
Published by Frontiers in Environmental Health, the study analyzed data from approximately 64.5 million pregnancies between 2003 and 2019 across more than 2,800 counties in 48 states. Researchers noted that even in regions not strongly associated with wildfires, such as the southeast U.S., wildfire pollution rates grew substantially during that period.
The research utilized two models of pollutants, one of which removed all fire-related pollution to determine how much was correlated with wildfires. Over the study period, about 65% of the days recording pollution levels above the National Ambient Air Quality Standard could be attributed to wildfire smoke.
Menglu Liang, the study's leading author and an assistant clinical professor of biostatistics at the University of Maryland, stated that while efforts to reduce other forms of pollution have protected pregnant people and unborn babies, wildfire smoke is offsetting those hard-won improvements. Liang noted that prenatal exposure is a significant public health concern because harms experienced before birth can echo for decades.
Some regions were disproportionately impacted by the smoke. In the Northwest, pollution rates from wildfires more than doubled over the study period. The study found that the highest burdens were located in rural, low-income areas with significant American Indian and Alaska Native populations, as well as areas facing maternity care shortages.
The study period did not include some of the most recent and explosive wildfire seasons in the United States and Canada, such as those in 2020, 2024, and the current year. By mid-July this year, more than 800 wildfires were burning across Canada, causing hazardous smoke levels in parts of the Midwest and northeast.
In Oregon, recent reports indicate the state is on track for its worst fire season on record, with nearly 1.8 million acres already burned. The previous record was set in 2024 with 1.9 million acres burned.
Scientists believe the inflammatory responses caused by wildfire smoke can harm the placenta, which is essential for fetal survival. Some pollutants may also cross the placental barrier, potentially affecting fetal growth and development. Recent studies have also correlated wildfire smoke exposure with increased risks of stillbirth and certain congenital anomalies.
