Wildfires Become Leading Source of Unhealthy Air Pollution for Pregnant Women in U.S., Study Finds

A study in Frontiers in Environmental Health analyzing 64.5 million U.S. pregnancies from 2003 to 2019 reveals that wildfire smoke has become the leading source of unhealthy air days for pregnant women. While overall prenatal PM2.5 exposure fell 34%, rising wildfire smoke offset these gains, accounting for 65% of high-pollution days by 2019. Low-income, rural, and Indigenous communities faced the highest burdens, raising concerns over risks like preterm birth and low birth weight.

Wildfire smoke pregnancy exposure

• ▪A study published in Frontiers in Environmental Health found that wildfire smoke became the dominant contributor to high-pollution days experienced during pregnancy in the United States by 2019.
• ▪By 2019, approximately 65% of prenatal fine particulate matter (PM2.5) exposure days exceeding U.S. Environmental Protection Agency safety standards were attributable to wildfire smoke.
• ▪The contribution of wildfire smoke to total prenatal fine particulate matter (PM2.5) exposure in the United States more than doubled from 3.7% in 2003 to 8.2% in 2019.

Declining non-wildfire PM2.5 trends

• ▪Reductions in air pollution from sources such as vehicles and industrial output between 2003 and 2019 were partially offset by rising wildfire smoke.
• ▪Daily prenatal fine particulate matter (PM2.5) exposure from all sources in the United States declined by an average of 34% between 2003 and 2019.

Adverse birth outcomes

• ▪Researchers believe that maternal inflammatory responses to wildfire smoke can damage the placenta and that pollutants may cross the placental barrier to affect fetal development.
• ▪Prenatal exposure to wildfire smoke is linked to adverse birth outcomes, including low birth weight, preterm births, stillbirth, and congenital anomalies.

Regional disparities in exposure

• ▪In the Northwest region of the United States, the contribution of wildfires to prenatal fine particulate matter (PM2.5) pollution rose from 5.1% to 13.3% between 2003 and 2019.
• ▪Wildfire smoke pollution rates grew substantially between 2003 and 2019 even in U.S. regions not strongly associated with wildfires, such as the Southeast.

Demographic disparities in exposure

• ▪Pregnant individuals living in areas with shortages of maternity care services experienced disproportionately high burdens of wildfire smoke pollution between 2003 and 2019.
• ▪Wildfire pollution burdens during pregnancy between 2003 and 2019 were highest for low-income, rural, American Indian, and Alaska Native communities.

Study methodology data scope

• ▪The study analyzed demographic and air quality data covering approximately 64.5 million pregnancies across 2,842 counties in 48 U.S. states between 2003 and 2019.
• ▪The study's computer models simulated air pollution by comparing a run with all PM2.5 sources to a run with fire-related pollution removed.
• ▪The study did not track whether pregnant individuals relocated during pregnancy or used protective measures like masks and air filters.

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