As wildfire seasons lengthen and heat waves deepen, a quiet but consequential question has emerged at the intersection of climate and human beginnings: what happens to a pregnancy caught between smoke and heat at once? Researchers at the University of Maryland, backed by $2.5 million from the National Institutes of Health, are now pursuing that answer across two decades and 6.5 million births — seeking to understand how overlapping environmental hazards shape the earliest moments of life, and whose lives bear the heaviest burden.
NIH-funded study examines combined pregnancy risks from heat and wildfire smoke
Pregnant people and babies face increased risks of preterm birth, low birthweight, hypertensive disorders, and gestational diabetes from combined heat and wildfire smoke exposure.
Combined exposure could mean greater damage to the heart and respiratory system
Mark
So the study is looking at heat and smoke together. But haven't researchers already shown that each one separately harms pregnancy?
Mimi
Yes—that's established. Heat causes preterm birth and low birthweight. Wildfire smoke does too. But almost no one has studied what happens when both hit at the same time, which is what's happening now in fire season across the West and Southwest.
Luke
Right, and that's the honest gap. We know A causes harm. We know B causes harm. But "A plus B causes more harm" is not automatically true—it depends on the mechanism. Are they additive? Synergistic? That's what they're trying to find out.
Mark
Why is pregnancy specifically vulnerable to both?
Mimi
During pregnancy, the body loses some of its ability to shed heat. Your heart and lungs are already working harder. So when you add heat stress on top of that, and then add tiny particles from smoke that lodge in your lungs, you're stacking strain on systems that are already at capacity.
Luke
That's the theory. The study will test it against 6.5 million births over twenty years. That's a real dataset.
Mark
And the communities most at risk?
Mimi
Low-income and minority populations. They're more likely to live in areas with worse air quality, less tree cover, fewer resources to escape heat. And they already have higher rates of gestational diabetes and hypertension.
Luke
The study should show whether that disparity gets worse when you add wildfire smoke to the picture. That's the policy question underneath all of this.
Mark
What happens after the study?
Mimi
Clinical guidance changes. Hospitals in high-risk areas get better tools to identify and protect pregnant people. Early-warning systems can alert vulnerable populations before a smoke event or heat wave hits.
Luke
If the findings are clear enough. A lot depends on whether the data actually shows a combined effect, and how strong it is.
The Pulse
- Wildfire smoke and extreme heat each independently raise the risk of preterm birth, low birthweight, gestational diabetes, and dangerous blood pressure disorders — and they are increasingly striking pregnant people simultaneously.
- Pregnancy strips the body of its usual defenses: temperature regulation falters, the heart and lungs are already strained, and microscopic smoke particles find a system with little reserve left to absorb the assault.
- The compounded threat falls hardest on low-income and minority communities already underserved by perinatal care, widening health gaps that existing research has barely begun to measure.
- A $2.5 million NIH-funded study led by epidemiologist Jennifer Stowell will analyze which pollutant combinations cause the most harm, which trimesters carry the greatest risk, and how vulnerability shifts across regions.
- If the research delivers what its architects hope, it could rewrite clinical guidance for pregnant patients in high-exposure areas and seed early-warning systems designed to reach the most vulnerable before harm is done.
As wildfire seasons lengthen and heat waves deepen, a quiet but consequential question has emerged at the intersection of climate and human beginnings: what happens to a pregnancy caught between smoke and heat at once? Researchers at the University of Maryland, backed by $2.5 million from the National Institutes of Health, are now pursuing that answer across two decades and 6.5 million births — seeking to understand how overlapping environmental hazards shape the earliest moments of life, and whose lives bear the heaviest burden.
Wildfire smoke and extreme heat have become familiar features of the American landscape, but researchers at the University of Maryland School of Public Health are now asking a question that has received surprisingly little attention: what happens when a pregnant person faces both at the same time? With a $2.5 million NIH grant, environmental epidemiologist Jennifer Stowell is leading a study that will draw on birth records from two decades and 6.5 million pregnancies to find out.
The risks from each hazard alone are already documented. Wildfire smoke and extreme heat are each linked to preterm birth, low birthweight, gestational diabetes, and hypertensive disorders of pregnancy — conditions that affect roughly 8 and 10 percent of pregnancies respectively, and that fall disproportionately on low-income and minority communities. What remains poorly understood is the effect of their overlap, which is becoming more common as climate change intensifies both wildfire seasons and heat waves.
Pregnancy amplifies the danger. The body's ability to regulate temperature diminishes, and the cardiovascular and respiratory systems are already working harder than usual. Fine particles from wildfire smoke penetrate deep into the lungs, adding strain to a system with little margin to spare. Researchers suspect the combined burden may cause greater harm than either hazard alone — but the evidence to confirm or quantify that suspicion has been scarce.
The study will examine which pollutant combinations matter most, which stages of pregnancy carry the highest risk, and how vulnerability differs across regions and communities. Its findings are expected to inform clinical guidance for pregnant patients in smoke- and heat-prone areas, and potentially to shape early-warning systems for the high-risk populations — particularly those in under-resourced rural communities — who currently have the least protection and the most to lose.
Wildfire smoke and extreme heat have become routine hazards across much of the United States, and researchers at the University of Maryland School of Public Health have begun a major investigation into what happens when pregnant people face both at the same time. The National Institutes of Health awarded the team a $2.5 million grant to study the combined effects of these exposures on maternal health—work that will draw on birth records spanning two decades and 6.5 million pregnancies.
The study, led by environmental epidemiologist Jennifer Stowell, arrives at a moment when the risks are no longer theoretical. Wildfire smoke and extreme heat each carry documented harms: preterm birth, low birthweight, gestational diabetes, and hypertensive disorders of pregnancy. Gestational diabetes affects roughly 8 percent of pregnancies in the United States; hypertensive disorders touch about 10 percent. Both conditions strike disproportionately at low-income and minority communities. What remains largely unknown is what happens when a pregnant person breathes smoke-laden air while also enduring dangerous heat—when the two hazards overlap, as they increasingly do.
Pregnancy itself creates vulnerability. The body's ability to regulate temperature declines during pregnancy, and the cardiovascular and respiratory systems are already working harder to support both mother and fetus. Tiny particles from wildfire smoke—measured as PM2.5—penetrate deep into the lungs. Heat stress compounds the load on an already taxed system. Researchers suspect that combined exposure could inflict greater damage to the heart and lungs than either hazard alone, but the evidence remains sparse. "We will look at the effect of exposure to all of these things at once, because they are increasingly happening all at once," Stowell said, noting that combined exposure could mean greater cardiovascular and respiratory strain for pregnant people and their babies.
The research will measure exposure to extreme heat, wildfire smoke particles, and other air pollutants against the incidence of serious pregnancy complications. Stowell and her colleagues will examine which combinations of pollutants matter most and which periods of pregnancy carry the highest risk. They will also map how vulnerability varies across different regions of the country—a crucial step toward understanding why some communities face steeper odds than others.
The findings are expected to reshape clinical guidance for pregnant people in areas where heat and smoke are now routine. They may also inform the design of early-warning systems aimed at protecting high-risk groups, particularly low-income and minority populations in under-resourced rural areas where perinatal care is already stretched thin. As climate change continues to intensify both wildfire seasons and heat waves, understanding how these exposures interact during pregnancy has moved from academic curiosity to urgent public health need. The study will help clarify what protection looks like for the millions of pregnant people now exposed to these hazards each year.
Notable Quotes
We will look at the effect of exposure to all of these things at once, because they are increasingly happening all at once.— Dr. Jennifer Stowell, principal investigator
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