Doctors have long known that heat puts a strain on the heart, kidneys and other organs. Those risks are exacerbated for pregnant people, as the body's processes for staying cool are altered.
It’s a problem that climate change, caused by the burning of fuels like gasoline and coal, is worsening. Intensifying extreme heat events, high temperatures well into the night and shattering weather records means more exposure for pregnant people, particularly in developing countries.
Here's what to know about the science of pregnancy and extreme heat:
Pregnancy changes the body in myriad ways, which can make it more difficult and uncomfortable to dissipate heat.
"An obvious thing is, pregnant people have a belly bump, depending how far along they are, and that’s a change in their surface 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 aimed at improving research on preventing extreme heat deaths. Heat leaves your body through your skin, so when the belly gets larger, the heat has farther to travel to escape.
As pregnancy progresses, the body burns more calories, creating internal heat. The heart has to work harder, which can already be strained by extreme heat. And people who are pregnant also need more liquid to stay hydrated, so they might get dehydrated more easily, according to the Environmental Protection Agency.
One way the body cools itself is by shunting blood toward the skin and away from the central organs, which is why a person's skin may flush and turn red when they get hot. Emerging research indicates that reduced blood flow to the placenta can affect the development of the fetus.
For pregnant people handling potent substances like pesticides, increased blood flow can also increase chemical absorption, said Dr. Chris Holstege, chief of the division of medical toxicology at the University of Virginia School of Medicine.
Research is beginning to show exposure to extreme heat even in the months before getting pregnant may affect a future pregnancy, said Cara Schulte, a researcher with the University of California Berkeley and the nonprofit Climate Rights International studying maternal health and heat.
During pregnancy, even short-term exposure to heat can increase the risk of severe maternal health complications, such as high blood pressure disorders of pregnancy, according to the EPA. That 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 those things are compounded by this difficulty that postpartum women have in caring for their children in the heat,” Schulte said.
As they grow up, children who are exposed to extreme heat in utero may be at increased risk of facing developmental challenges throughout their lives, potentially related to adverse outcomes such as preterm birth or low birth weight, Schulte said.
"This is a hugely understudied thing,” said Bershteyn, adding that a lot of what we know comes from studies recruiting athletes, soldiers or fit young people. "There hasn’t been the same level of commitment to women’s health research."
