University of Utah Study Ties Mixed Pollutants to Preterm Birth
A University of Utah study of nearly 45,000 first-time expectant mothers found that repeated exposure to a mixture of air pollutants during early pregnancy is associated with nearly three times greater odds of preterm birth. The study, published in June 2025, used artificial intelligence to analyze pollutant exposure across a large cohort of Utah pregnancies.
The research focused on what happens when multiple pollutants combine, not just individual contaminants. Exposure to a mixture of ozone and fine particulate matter (PM2.5) during the late first trimester showed the strongest link to early delivery.
“Early pregnancy is a critical period because the placenta and arteries that supply blood and oxygen to the fetus are still developing.”
Michelle Debbink, associate professor of obstetrics and gynecology, University of Utah, June 2025
Debbink added that pollutant exposure at that stage could impair placental development, increasing the risk of preeclampsia and preterm delivery. Repeated exposures, she said, may cause inflammation that accumulates over time.
The EPA’s AQI Only Measures One Pollutant at a Time
The Air Quality Index rates air quality based on whichever single pollutant poses the greatest individual harm on a given day. It does not account for the combined effect of multiple pollutants present simultaneously.
Because the EPA evaluates each pollutant separately, it may classify a day’s air as “moderate” or even “good” while a pregnant person is still inhaling a mixture that carries real health risk. The University of Utah researchers say their findings raise direct questions about whether AQI ratings are missing serious public health threats.
Pregnancy makes this worse. Expectant mothers have higher oxygen demands, meaning they inhale a greater volume of whatever is in the air. Utah also has several non-attainment areas where pollution levels persistently exceed federal health standards, and the state has recorded some of the worst short-term air quality in the country.
Lead author Brenna Kelly framed the exposure problem simply: “People are exposed to multiple things at once, over multiple times.”
What This Costs
Preterm birth carries high financial and medical consequences. The Centers for Disease Control and Prevention estimates that preterm birth and low birth weight cost the U.S. healthcare system more than $26 billion annually. Infants born preterm face raised risks of respiratory illness, developmental delays, and long-term disability. Those costs fall on families, state Medicaid programs, and neonatal intensive care units.
Utah’s non-attainment designations mean the state is already out of compliance with existing federal standards. A regulatory framework that only measures single-pollutant exposure leaves the mixture risk entirely unaddressed.
What You Can Do Now
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Contact EPA Administrator Lee Zeldin’s office at (202) 564-4700 and demand that the agency commission a formal review of multi-pollutant AQI methodology. Reference the University of Utah’s June 2025 study and ask that mixture exposure be factored into air quality ratings.
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Call your U.S. senators at (202) 224-3121 and urge them to protect the Clean Air Act’s mandate for regular review of National Ambient Air Quality Standards. The EPA is currently under pressure to weaken those reviews.
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Contact the Utah Division of Air Quality at (801) 536-4000 and ask what steps the state is taking to address non-attainment areas, particularly near residential zones with high proportions of pregnant residents.
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Contact your state legislators if you live in a non-attainment area. Ask them to require the Utah Department of Environmental Quality to incorporate multi-pollutant exposure modeling into its public health advisories for pregnant residents.
Sources
Utah News Dispatch: Utah Air Pollution Linked to Preterm Birth, University Study Finds EPA: Air Quality Index Basics and How It Is Calculated CDC: Preterm Birth Data and Statistics Including Annual Costs EPA: Current Nonattainment Area Designations by State