During the dog days of summer, you might prefer to stay indoors when exercising. However, if you enjoy being in the heat, or prefer activities that lend themselves to the outdoors — like running, biking, hiking, etc.– you might be wondering if you can safely work out in the heat during pregnancy. After all, if you are pregnant, you’ve likely been told to minimize heat exposure and avoid things like saunas, hot baths, and exercise in the heat.
But why is that? Where does the caution about heat exposure during pregnancy come from, and how do you ensure that your preferred mode of physical activity is a safe one?
This article will help you understand the basis for the concern about overheating during pregnancy, provide you with the very latest research on this topic, and most importantly, provide simple guidance to help you stay safe while enjoying the types of activities you love.
Where the Concern about Overheating During Pregnancy Comes From
Once the body becomes pregnant, keeping the growing fetus safe and developmentally on track is of the utmost importance. And with respect to fetal body temperature, preventing it from climbing much higher than baseline is critical, especially in the first trimester. This is because essential organ development is occurring during this time and those processes can be adversely affected by high spikes in body temperature.
It’s important to understand that fetal body temperature is contingent upon maternal body temperature. Seminal research done on this topic (from the 1960s) was performed on animals. This research showed that when maternal body temperature got too high (above 102° Fahrenheit), it can result in birth defects, especially during the earlier part of the first trimester, when critical brain and organ development is occurring (Edwards, 1967). This is where the guidance to limit heat exposure during pregnancy comes from.
The Fascinating Ways the Pregnant Body Dissipates Heat
While the research findings above might sound concerning, fear not, because the pregnant body naturally adapts to allow for greater heat dissipation. Specifically, the following changes occur:
- Sweating begins at a lower body temperature. You start sweating sooner to cool off.
- More heat is lost through respiration. Breathing rate increases by 50% during pregnancy (ACE, 2011).
- There is an increased skin-to-environment heat transfer. Due to increased blood flow during pregnancy.
So, even though exercise does elevate body temperature, the pregnant body’s natural adaptations help safeguard against any potential risk to the fetus. That said, it is still important to follow the safety guidelines below to ensure that you don’t do anything to inhibit your body’s ability to dissipate heat.
What New Research is Showing
Very recent research, from 2019, looked at body temperature in humans, and determined that people can safely exercise in hotter conditions than previously thought.
Specifically, it said that pregnant people can safely exercise for up to 35 minutes at 80 to 90 percent max heart rate in 77° at 45% relative humidity (Ravenelli et. al, 2019). In addition, exercising in the water and spending time in saunas is considered safe, as long as certain safety guidelines (outlined below) are followed.
Guidelines for Safe Heat Exposure During Pregnancy
While the pregnant body naturally adapts to allow for greater heat dissipation, it is important to avoid those conditions that could make heat dissipation more difficult. Therefore, it is recommended to avoid the following (Ravenelli et. al, 2019):
- Prolonged (>35 min), high-intensity exercise in heat above 77° F and 45% relative humidity
- Water immersion (>92° F) for more than 45 min
- Saunas (>20 min) above 158° F and 15% relative humidity
- Hot tubs/baths (>104°) F for more than 20 min
- Hot yoga
In addition to avoiding the activities above, here are some additional tips to minimize the risk of overheating:
- Drink Water! Hydration is essential for so many reasons during pregnancy, including enabling you to keep sweating
- Wear clothing that allows for sweat evaporation
- If exercising outside, do so during the cooler times of day (avoid 10am-4pm)
If you follow the guidelines above, and you don’t have any other pre-existing conditions, rest assured that you can exercise in warmer conditions and still experience a safe and healthy pregnancy.
Want Additional Resources?
For additional resources to help you exercise safely and effectively during pregnancy, explore our training programs and services. You’ll find a variety of offerings tailored to different needs — from education, to self-guided programs, to the ability to work with an expert coach.
Or, if you’re a health & fitness pro interested in coaching pre & postnatal clients, check out our ProNatal Education & Certification.
American Council on Exercise. (2011). ACE Group Fitness Instructor Manual: A Guide for Fitness Professionals. San Diego, Print.
Edwards. M.J. (1967). Congenital defects in guinea pigs. Following induced hyperthermia during gestation. Arch Pathol., 84(1):42-8.
Ravanelli, N., Casasola, W., English, T., Edwards, K.M., Jay, O. (2019). Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis. British Journal of Sports Medicine, 53(13), 799-805.