Most medical authorities advise pregnant women to avoid saunas, especially during the first trimester. The core concern is overheating: when your body temperature rises above 102°F (39°C), it can pose risks to fetal development. While limited research exists on sauna use specifically during pregnancy, the available evidence on maternal hyperthermia has been enough for organizations like the American College of Obstetricians and Gynecologists (ACOG) and the NHS to recommend caution.
Why Heat Is a Concern During Pregnancy
Your body handles heat differently when you’re pregnant. Blood volume increases, your cardiovascular system is already working harder, and your ability to regulate temperature shifts. In a sauna, your body can’t cool itself effectively through sweating because the surrounding air is already hot and often humid. This means your core temperature climbs faster than it normally would.
The specific worry is a condition called maternal hyperthermia, where core body temperature rises significantly above normal. When this happens during the first 12 weeks of pregnancy, it has been associated with an increased risk of neural tube defects, which are serious problems with the development of the baby’s brain and spinal cord. Core temperatures above 103°F (39.5°C) during the first trimester have been linked to a higher risk of both neural tube defects and miscarriage. The Mayo Clinic advises keeping your core temperature below 102°F as a safety threshold.
ACOG groups saunas alongside hot tubs and fever as heat sources associated with neural tube defect risk. The first trimester is the most vulnerable window because that’s when the neural tube is forming, but overheating later in pregnancy still carries risks like dehydration and fainting, both of which can be dangerous when you’re carrying.
Saunas vs. Hot Tubs vs. Exercise
It’s worth understanding that not all heat exposure carries the same level of risk. ACOG notes that exercise during pregnancy is not expected to raise core body temperature into the danger zone, even though it generates heat. The difference is that when you exercise, your body can still cool itself through sweating and increased blood flow to the skin. In a sauna or hot tub, those cooling mechanisms are far less effective because the environment itself is working against them.
Hot tubs may actually pose a greater risk than dry saunas because water transfers heat to your body about 25 times more efficiently than air. A hot tub set to 104°F (40°C) can raise your core temperature faster than sitting in a sauna at a higher ambient temperature. The NHS recommends that pregnant women using hydrotherapy pools keep the water temperature below 95°F (35°C), and notes that hot tubs reaching 104°F should be avoided entirely.
If You Choose to Use a Sauna
Some women, particularly in countries like Finland where sauna use is deeply cultural, continue using saunas during pregnancy. If you decide to do so after weighing the risks, there are practical steps that reduce the danger.
- Limit your time. Stay in the sauna for no more than 15 minutes. The longer you’re exposed, the higher your core temperature climbs.
- Choose lower temperatures. A sauna should not feel uncomfortably hot. If the heat feels intense, it’s too much.
- Stay hydrated. Drink water before, during, and after. Dehydration compounds the risk of fainting and can reduce blood flow to the uterus.
- Avoid the first trimester. The risk of neural tube defects is concentrated in the first 12 weeks, making this the worst time for significant heat exposure.
- Sit on a lower bench. Heat rises, so the air near the floor of a sauna is cooler than at the top.
Warning Signs to Watch For
Your body will give you signals before you reach a dangerous core temperature. Dizziness, lightheadedness, nausea, and a sensation of excessive warmth are all signs to leave immediately. Feeling like you might faint is a particularly urgent signal. If any of these occur, step out, sit somewhere cool, and drink water. Don’t push through discomfort hoping it will pass.
Pregnancy already lowers your blood pressure in the second trimester, which makes fainting more likely in hot environments even without a dangerously elevated core temperature. A fall in a sauna is its own serious risk, separate from any effect on fetal development.
The Bottom Line on Risk
The honest reality is that there isn’t a large body of research studying pregnant women in saunas directly, for obvious ethical reasons. Most of what we know comes from studies on maternal fever and hot tub use, then extrapolating to saunas. The NHS acknowledges this gap plainly: there’s little research, and the recommendation to avoid saunas is precautionary.
That said, the precaution exists for a real reason. Neural tube defects are serious, the mechanism linking high core temperature to developmental harm is well established, and the benefit of a sauna session doesn’t outweigh even a small increase in risk for most people. A brief session in a moderate sauna later in pregnancy is a very different scenario from a long soak in a hot tub during week six, but most guidelines don’t make that distinction because the safer advice is simply to wait until after delivery.