Doctors have long known that heat puts strain on the heart, kidneys and other organs. These risks are exacerbated for pregnant women because the body’s processes for staying cool are impaired.
The problem is that climate change, caused by the burning of fuels like gasoline and coal, is getting worse. Intensifying extreme heat events, high temperatures late into the night and shattering weather records mean increased exposure for pregnant women, particularly in developing countries.
Here’s what you need to know about the science of pregnancy and extreme heat:
Pregnancy changes the body in multiple ways, which can make heat dissipation more difficult and uncomfortable.
“One thing that’s obvious is that pregnant women have a bump in their stomach, depending on what state they’re in, and that’s a change in their surface area-to-volume ratio,” said Anna Bershteyn, an associate professor at New York University’s Grossman School of Medicine and director of Project HEATWAVE, an initiative to improve research on preventing deaths from extreme heat. Heat leaves your body through your skin, so when the belly grows, the heat has to travel a greater distance to escape.
As pregnancy progresses, the body burns more calories, creating internal heat. The heart has to work harder, and the extreme heat can already put a strain on it. And pregnant people also need more fluids to stay hydrated, so they might become dehydrated more easily, according to the Environmental Protection Agency.
One way the body cools itself is by directing blood toward the skin and away from the central organs. This is why a person’s skin can blush and turn red when it heats up. New research indicates that reduced blood flow to the placenta may affect fetal development.
For pregnant women handling potent substances like pesticides, increased blood flow can also increase the absorption of chemicals, said Dr. Chris Holstege, chief of the division of medical toxicology at the University of Virginia School of Medicine.
Research is beginning to show that exposure to extreme heat, even in the months before a pregnancy, can affect a future pregnancy, said Cara Schulte, a researcher at the University of California, Berkeley and the nonprofit Climate Rights International who studies maternal health and heat.
During pregnancy, even short-term exposure to heat can increase the risk of serious maternal health complications, such as pregnancy-related high blood pressure disorders, according to the EPA. This includes preeclampsia, a condition that can be fatal for both mother and child.
Heat can also worsen anxiety, depression and feelings of isolation, and once the baby is born, “all of these things are made worse by the difficulty postpartum women have caring for their children in the heat,” Schulte said.
As they grow, children exposed to extreme heat in utero may be at increased risk of developmental problems throughout their lives, potentially linked to adverse outcomes such as premature birth or low birth weight, Schulte said.
“It’s an extremely understudied question,” Bershteyn said, adding that much of what we know comes from studies that look at recruiting athletes, soldiers or fit young people. “There hasn’t been the same level of commitment to women’s health research.”
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Associated Press reporter Dorany Pineda contributed to this report.
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Follow Melina Walling on X @MelinaWalling and Bluesky @melinawalling.bsky.social.
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