Are saunas safe during pregnancy?

What does the evidence say about saunas during pregnancy?

1. Raising your core body temperature above about 102°F (38.9°C) in the first trimester has been linked to a higher risk of neural tube defects in observational studies. 1
2. Saunas run much hotter than most hot tubs and can raise your core temperature faster, with just 10 to 15 minutes enough to reach a concerning level. 1
3. Pregnancy itself makes you more prone to heat-related illness, since changes in blood flow and body-temperature regulation lower your normal heat tolerance. 2
4. Infrared saunas still raise your core temperature even though they heat your body more than the air around you, so the same avoidance guidance applies to them as to traditional saunas. 1

Is saunas safe in each trimester?

• First trimester. This is the highest-stakes window, since a key stage of the baby's neural development happens around weeks 3 to 4. Avoid saunas and steam rooms entirely during the first trimester.
• Second trimester. Keep avoiding them. Pregnancy-related changes in blood flow make heat-related dizziness and fainting more likely now.
• Third trimester. Keep avoiding them. With your balance already shifted from your growing belly, heat-related lightheadedness is riskier now than earlier in pregnancy.