Doctors warn wildfire smoke could raise preterm birth risk

SEATTLE - A University of Washington-led study is raising new alarms over the health impacts of wildfire smoke on pregnancy. Researchers found exposure to wildfire-related air pollution is associated with higher odds of preterm birth, especially in the western United States.

Dr. Catherine Karr, a UW Professor of Pediatrics and Environmental Health has long studied how the environment influences children.

"It’s hard to ignore wildfire smoke when you live in the Pacific Northwest because it’s a really important issue," she said, noting people in the region have "experienced the reality of increasing impacts."

More Smoke, Lasting Longer

Dr. Karr has observed that the severity and duration of smoke events are growing locally.

"Kids are growing up and each year they’re seeing exposure," she said.

She warned that exposure is no longer a rare event and asked if this could lead to "chronic" health issues throughout children’s lives.

Last summer, skies above Seattle turned an eerie orange as wildfire haze hung heavy over Puget Sound. Across the water in the Olympics, smoke from the Bear Gulch Fire was so thick that the town of Hoodsport briefly had the worst air quality in the entire nation. At the same time, fires near Leavenworth reduced forests to ashes, sending plumes of smoke drifting across the Cascades. 

"When you burn trees or wildlands, some of the components of that smoke are similar to the kind of air pollutants we see in everyday sources," said Dr. Karr.

Study: Higher Odds of Early Delivery

The UW-led study found that even small increases in wildfire-related pollution are linked to a measurable rise in risk. Karr explained researchers looked at increases of 1 microgram per meter cubed, noting a roughly 7% higher risk of preterm birth tied to that increase.

"These are lifelong consequences for children and that’s why it’s a big deal," she said, pointing to concerns beyond temporary symptoms like irritated eyes and coughing. 

Conditions such as asthma in children are among the long-term risks being examined.

Why Pregnancy Is Especially Vulnerable

"I think when you’re pregnant, it’s realizing that it’s a sensitive time and that the fetus is particularly vulnerable to wildfire smoke," said Dr. Karr.

She explained that during the second trimester, the placenta is undergoing "its most rapid growth and developmental changes," making it more susceptible to disruption.

"So how it works is you inhale the smoke, it gets in your lungs, and there’s some biological processes that get unleashed right there in the lung," she explained. "That spills over into the blood stream and travels to organs including the placenta."

Higher Risk in the West

The research was conducted through the ECHO Study (the Environmental Influences on Child Health Outcomes program), funded by the National Institutes of Health. More than 20,000 pregnant women from nearly every U.S. state participated in the study.

"Unfortunately for us in the west, but perhaps maybe not surprisingly, we tend to have more intense and higher exposures to wildfire smoke," shared Dr. Karr. "We did find that the risk was a bit higher."

She said the impacts are not limited to early life. Both early and late life stages appear to be more sensitive to these exposures.

Mitigation and Prevention

Karr said there are ways to reduce risk. 

"We will have less preterm births if everyone’s able to protect themselves," she noted.

Her recommendations include:

• Get into a safe indoor environment — doing so can reduce risk by half.
• Wear an N95 mask to filter harmful particles.
• Use indoor air filtration with a MERV-13 or higher rated filter and replace it regularly.

During severe smoke episodes, she advises patients to consider what room in their home they could safely stay in for extended periods. It should be a space with few doors and windows, she suggested sometimes a bedroom, though families with children may opt for a different area.

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