A University of Washington study finds that wildfire smoke exposure during pregnancy increases the risk of preterm birth, especially during mid-gestation, highlighting an urgent maternal-health concern in fire-prone regions.
- Pregnant women exposed to wildfire smoke were more likely to deliver early
- The strongest risk appeared around the 21st week of pregnancy
- Western U.S. women faced the greatest exposure and preterm-birth risk
Every tenth baby in America arrives early, before 37 weeks, a major cause of infant complications. Now, new research suggests wildfire smoke could be part of the reason.
A University of Washington-led study, published in The Lancet Planetary Health, examined more than 20,000 births across the U.S. and found that exposure to wildfire smoke during pregnancy significantly increased the risk of preterm birth (1✔ ✔Trusted Source
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Inside the Study
Researchers analyzed data from 20,034 births between 2006 and 2020 as part of the National Institutes of Health’s Environmental Influences on Child Health Outcomes (ECHO) program. Using air-quality modeling, they estimated how many days each pregnant person was exposed to wildfire-related fine particles (PM2.5) and how intense that exposure was.
Those exposed to higher concentrations of wildfire smoke, especially levels exceeding 10 micrograms per cubic meter, were more likely to give birth early. The risk peaked around the 21st week of gestation, a crucial stage when the placenta grows most rapidly and supports fetal development.
Dr. Allison Sherris, the lead author, explained, “Air pollution is already known to raise preterm-birth risk, and our findings show wildfire smoke is no exception. This issue is inseparable from maternal and infant health.”
Why the Timing Matters
Co-author Dr. Catherine Karr noted that the second trimester may be the most vulnerable window: “The placenta undergoes its richest growth at this stage. Some smoke particles are so tiny they can cross into the bloodstream, reaching the placenta or fetus.”
The link was strongest in the Western U.S., where smoke concentrations were highest and exposure days most frequent. In these regions, every small rise in average wildfire PM2.5 was tied to an increase in preterm-birth odds.
Beyond the Numbers
Wildfire smoke is a complex mix of gases and fine particles that vary by geography and fuel source. In the West, fires burn closer to populated areas, producing fresher, more reactive smoke. In contrast, the Midwest often experiences older, long-range smoke that’s chemically different. These differences — along with co-factors like heat and housing quality — may shape how smoke harms pregnancy.
The findings underline an emerging truth: environmental exposure during pregnancy isn’t limited to city pollution — wildfire smoke is now a growing global risk.
Protecting Mothers and Babies
The researchers urge both public-health agencies and clinicians to include pregnant people in wildfire-smoke advisories. Simple actions — like staying indoors with filtered air, wearing N95 masks outdoors during smoke days, or monitoring local air-quality alerts — could lower exposure.
“We can’t prevent every fire,” Sherris said, “but we can help people protect themselves when smoke fills the air.”
Final Takeaway
Wildfire smoke isn’t just a respiratory threat — it may quietly affect pregnancies too. As fires become more frequent and severe, protecting expectant mothers from exposure could safeguard the next generation’s health.
Until more is known, awareness, cleaner indoor air, and timely guidance from healthcare providers remain the simplest defences for both mother and baby.
Reference:
- Wildfire-specific fine particulate matter and preterm birth: a US ECHO Cohort analysis – (https://www.thelancet.com/journals/lanplh/article/PIIS2542-5196(25)00202-5/fulltext)
Source-Medindia