Millions of Americans are under a heat advisory as record temperatures scorch much of the country. Pregnant people are among the most at risk – they are more susceptible to heat exhaustion and other ailments. Extreme heat is associated with stillbirth, preterm birth and other adverse pregnancy outcomes. “When we think of heat, a lot of us think of discomfort,” said Blair Wylie, an OB-GYN who leads Columbia University’s Collaborative for Women’s Environmental Health. “For pregnant patients, not only is it uncomfortable, it’s actually risky.”
Public health experts and physicians explain the risks of extreme heat during pregnancy and share ways to stay safe.
What are the risks to pregnant people during heatwaves?
Pregnant people are more at risk for heat illness and heatstroke. This is due to the physical strain of carrying a developing fetus and hormonal changes that can affect thermoregulation.
“The fetus, the amniotic fluid, the placenta are all sitting there and are generating heat. They are a metabolic load,” said Wylie. “So heatwave aside, when you’re pregnant you have to dissipate that heat.”
To sustain blood flow to the placenta and the fetus, the blood volume of pregnant people increases by roughly 40% to 50% during pregnancy. The increased blood volume and amniotic fluid and other physiological changes mean pregnant people need to consume more liquids – and are more easily dehydrated.
Pregnant people are also at risk for preterm delivery, low birth weight and stillbirths.
“Extreme heat can create problems with staying pregnant through term,” said Nathaniel DeNicola, an OB-GYN in Newport Beach, California. “Fatigue and dehydration trigger the hormones that are involved in contractions and eventually, if that cascade continues, it produces labor.”
What are the symptoms of heat illness?
Common symptoms include dehydration, nausea, vomiting, dizziness, rapid heartbeat and confusion. While these symptoms are similar to what non-pregnant people experience, there is an added risk of complications.
“You might not get to the point of having a heatstroke, but you can still have a negative consequence to your pregnancy,” said Wylie.
Among pregnant people, who is the most vulnerable to heat?
Black and Hispanic communities are disproportionately affected by extreme heat. They are more likely to live in urban heat islands – areas where high concentrations of asphalt and buildings and a dearth of green space cause a higher concentration of heat – and more likely to work outdoors or in other professions with high exposure to heat.
“Communities of color may be exposed to neighborhoods that have less green space and more concrete,” said Wylie. “They may be at higher risk of being unable to afford utilities and that may increase their susceptibility to extreme heat events.”
They are also more likely to be exposed to harmful pollutants and poor air quality, which are also linked to poor birth outcomes.
“We know that even without environmental exposures, maternal health outcomes are worse for Black mothers,” said Rupa Basu, an epidemiologist with the California Environmental Protection Agency. “And what’s most concerning for me is that this disparity is increasing.”
Black women are three times more likely to die from pregnancy-related complications than white women, with risk spanning income and education levels.
How can pregnant people stay safe during heatwaves?
“Avoiding the outdoors during peak heat hours, drinking a lot of fluids, wearing loose-fitting clothing, and staying in cool, air-conditioned environments, if possible,” Basu said. “Going to a movie theater or indoor shopping mall because that’ll be air conditioned might sound so simple, but is actually really beneficial.”
Experts also recommended taking it easy.
“There’s a lot of emphasis on maintaining fitness during pregnancy, which is great,” said DeNicola. “But pushing yourself beyond your limit especially during hot times is not good. You should be tailoring your exercises and scaling back appropriately.”
He added that people should plan outdoor time based on when the heat and air pollution will be lowest.
“Pregnant women have enough to worry about – they already are given all these lists of things they can’t drink and can’t eat and fun they can’t have, [but] they can’t control the air they breathe or the heat outside,” DeNicola said. “But there are some ways you can protect yourself against extreme heat and a lot of times knowledge is empowering.”
