The frequency and intensity of extreme heat continue to rise, and many negative health impacts are associated with these rising temperatures.
Although it is projected not to be as hot as last summer, 2025 is still on track to be the second or third warmest year on record. Many parts of the US have been experiencing significant heat waves with temperatures going into the triple digits. Last month, the eastern half of the US faced extreme heat conditions, with more than 185 million people under warnings.
Heat stress remains the leading cause of weather-related deaths and can exacerbate underlying conditions, including cardiovascular disease, diabetes, and mental illness. According to the Environmental Protection Agency (EPA), a total of 14,000 Americans have died directly from heat-related causes since 1979. It turns out the true number, however, may actually be significantly higher due to the challenges of tracking heat-related deaths.
Last summer, we covered two of the many groups vulnerable to heat-related illnesses: children and athletes. This year, we will focus on another population: pregnant individuals.
Health impacts of extreme heat on pregnant people
Being exposed to extreme heat for long periods of time is both uncomfortable and dangerous for everyone, especially if you’re not taking appropriate precautions. Such heat poses specific health risks during pregnancy, including increased likelihood of complications like pre-eclampsia and gestational diabetes, fetal abnormalities, maternal hospitalizations, and severe maternal morbidity. Other adverse outcomes, such as stillbirth, low birth weight, and preterm birth, also increase.
According to the Centers for Disease Control and Prevention (CDC), one day of extreme heat can increase the risk of pregnancy complications. Studies show that these risks are especially high in Black or Hispanic communities. For instance, for Black women, an additional day of exposure to extreme heat during the third trimester doubles the odds of hospitalization compared to their white counterparts.
In a May 14 article in Time magazine, Shruthi Mahalingaiah, Associate Professor of Environmental, Reproductive, and Women’s Health at Harvard T.H. Chan School of Public Health, explained why pregnant people are at heightened risk:
“The pregnant woman’s body is already undergoing vast changes to accommodate supporting a fetus, and it’s harder to regulate and especially cool the fetal environment to a healthy range. . .The fetus doesn't have its own capacity to regulate its temperature, and we know that [much of] the development of the fetal organs are temperature sensitive.”
Climate change means more pregnancy heat-risk days
Climate Central’s newest report, Climate change increasing pregnancy risks around the world due to extreme heat, quantifies how climate change is associated with increased preterm births worldwide. This study used Climate Central’s Climate Shift Index (CSI) to quantify how climate change has altered the frequency of daily temperatures across the globe.
Results from this report are jarring, with climate change adding at least 48% more pregnancy-risk days in the US alone. The study found that on average, every US state experienced at least one additional week’s worth of pregnancy heat risk annually, and thirteen states experienced at least two additional weeks.
To learn more about this resource from Climate Central, visit their CSI map tool.
How to keep cool during pregnancy
Understanding heat-related illnesses and immediate action steps to take is important as we prepare for more extreme heat conditions in the weeks and years to come. Here are some tips from the Pediatric Environmental Health Specialty Unit (PEHSU) and CDC on how to stay cool and safe during the summer:
- On hot days, spend time in cool or air-conditioned areas
- Take lukewarm baths (not cold) when you are feeling overheated
- Wear lightweight, comfortable, light-colored clothing
- Avoid the sun during peak hours: 10 am to 4 pm.
- If you are outdoors, wear a wide-brimmed hat and stay in the shade as much as possible
- Do not engage in strenuous activities
- Drink lots of water and limit caffeinated and sugary beverages if possible
- Check your local heat risk and air quality (You can use this CDC HeatRisk Dashboard to track the heat risk forecast in your area)
- Learn how to recognize heat-related illness
- Have a plan, especially in case of power outages
If you or someone you know is experiencing symptoms of heat-related illness, seek medical assistance and call the doctor or 911 right away, and cool the person quickly.
We invite you to explore the following resources for additional information and tips:
- Climate Central (2025). Climate change increasing pregnancy risks around the world due to extreme heat (2020 - 2024).
- Collaborative for Health and Environment (2019). Climate Change and Heat: Health effects, adaptation strategies, and the benefits of mitigation.
- Collaborative for Health and Environment (2023). Playing on Plastic: Artificial Turf Hazards and Safe Alternatives.
- Collaborative for Health and Environment (2024). Summer Heat (Climate Change Version).
- Pediatric Environmental Health Specialty Unit (2021). Extreme Heat Safety during Pregnancy.