Are steam rooms safe during pregnancy?

What does the evidence say about steam rooms during pregnancy?

1. A temperature over 101°F counts as a fever, and studies have linked hyperthermia or fever before the 6th week of pregnancy to a small increased chance of neural tube defects; high temperatures after week 6 aren't expected to raise that particular risk. 1
2. MotherToBaby's practical guidance is to limit sauna or hot tub use during pregnancy and take extra care in hot climates, without carving out steam rooms as a separate, lower-risk category. 1
3. An expert group review puts the teratogenic threshold at a maternal core temperature rise of about 1.5 to 2°C above baseline, roughly 39°C (about 102°F), and notes a 20-minute dry sauna at 70°C is one example that stayed within safe limits in research, though data confirming these thresholds specifically in pregnant women remains limited. 2
4. A scoping review of 84 studies from 2010 to 2020 found a consistent pattern: gestational heat exposure was positively associated with preterm birth, lower birth weight, and other adverse outcomes across the literature, even though the studies varied widely in how they defined and measured heat exposure. 3
5. In heat-exposure research, high humidity cut the body's maximum evaporative cooling capacity by roughly two-thirds compared with dry heat and pushed core temperature about 0.5°C higher for the same effort, the physical reason humid air makes it harder for your body to cool itself than dry heat at a similar temperature. 4

Is steam rooms safe in each trimester?

• First trimester. The narrowest window of concern is actually before week 6, often before a positive test, when studies link hyperthermia to a small increased chance of neural tube defects. MotherToBaby says temperatures after week 6 aren't expected to add that particular risk.
• Second trimester. Because humid air blunts sweat evaporation, it's harder to gauge how hot you're actually getting in a steam room than in a dry sauna with a known temperature, which is a good reason to keep skipping it through this trimester too.
• Third trimester. The proposed mechanisms for heat-related harm, including reduced blood flow to the placenta and dehydration-driven drops in uterine blood flow, are systems already under more strain later in pregnancy, so a cool shower is the lower-risk way to relax now.