A University of Washington-led study is raising serious concerns about the health impacts of wildfire smoke on pregnancy, with researchers finding that exposure to wildfire-related air pollution significantly increases the odds of preterm birth, with the effect particularly pronounced in the western United States where smoke events have become more frequent and severe.
Dr. Catherine Karr, a UW Professor of Pediatrics and Environmental Health who has dedicated her career to studying how environmental factors influence children’s health, indicated that the escalating severity and duration of wildfire smoke events in the Pacific Northwest have made this issue impossible for residents to ignore.
“It’s hard to ignore wildfire smoke when you live in the Pacific Northwest because it’s a really important issue,” Dr. Karr stated, noting that people in the region have “experienced the reality of increasing impacts” as wildfire seasons have extended and intensified in recent years.
Dr. Karr has observed that both the severity and duration of smoke events are growing locally, creating a new normal where children grow up experiencing significant smoke exposure year after year rather than encountering it as a rare occurrence.
“Kids are growing up and each year they’re seeing exposure,” she stated, expressing concern about whether this repeated annual exposure could lead to “chronic” health issues that persist throughout children’s lives.
Last summer provided a stark illustration of the smoke impacts Dr. Karr describes. Skies above Seattle turned an eerie orange as wildfire haze hung heavy over Puget Sound, reducing visibility and creating hazardous air quality conditions. Across the water in the Olympics, smoke from the Bear Gulch Fire was so thick that the town of Hoodsport briefly registered the worst air quality in the entire nation. Simultaneously, fires near Leavenworth reduced forests to ashes, sending plumes of smoke drifting across the Cascades and blanketing communities on both sides of the mountain range.
“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,” Dr. Karr explained, noting that wildfire smoke contains particulate matter and chemical compounds that have well-documented health effects similar to urban air pollution but often at much higher concentrations during intense smoke episodes.
The UW-led study found that even small increases in wildfire-related pollution are linked to measurable increases in preterm birth risk. Dr. Karr explained that researchers examined increases of just 1 microgram per cubic metre of air, a relatively small increment, and found a roughly 7% higher risk of preterm birth associated with that increase in exposure.
“These are lifelong consequences for children and that’s why it’s a big deal,” she stated, emphasising that the concerns extend far beyond the temporary symptoms like irritated eyes, scratchy throats, and coughing that people experience during smoke events. The preterm births linked to smoke exposure can lead to developmental challenges, respiratory problems, and other health issues that affect children throughout their lives.
Conditions such as asthma in children are amongst the long-term health risks being examined by researchers studying the lasting impacts of early-life smoke exposure. Children born prematurely face elevated risks for numerous health challenges including respiratory diseases, developmental delays, learning disabilities, and chronic health conditions that can persist into adulthood.
“I think when you’re pregnant, it’s realising that it’s a sensitive time and that the foetus is particularly vulnerable to wildfire smoke,” Dr. Karr stated, explaining the biological mechanisms that make pregnancy a period of heightened vulnerability to air pollution.
She explained that during the second trimester, the placenta undergoes “its most rapid growth and developmental changes,” making this period particularly susceptible to disruption from environmental exposures. The placenta serves as the critical interface between mother and foetus, facilitating oxygen and nutrient transfer whilst filtering out harmful substances, and any disruption to its development can have cascading effects on foetal health.
“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 bloodstream and travels to organs including the placenta.” This pathway means that smoke exposure does not just affect the mother’s respiratory system but triggers inflammatory responses and oxidative stress that circulate throughout the body and can interfere with placental function and foetal development.
The research was conducted through the ECHO Study (Environmental Influences on Child Health Outcomes programme), a major research initiative funded by the National Institutes of Health. More than 20,000 pregnant women from nearly every US state participated in the study, providing a robust dataset that allowed researchers to examine smoke exposure impacts across diverse geographic regions and populations.
