Using hot tubs, whirlpools, saunas, or steam rooms when you’re pregnant can be risky because of the high temperatures involved. In laboratory animals, exposure to high levels of heat during pregnancy has been known to cause birth defects or miscarriage.
Studies involving humans suggest that pregnant women whose core body temperatures rise significantly during the early weeks of pregnancy may stand an increased risk of miscarriage or having babies with neural tube defects (spina bifida, for example).
However, problems typically occur only if the mother’s core temperature rises above 102 degrees Fahrenheit (or about 39 degrees Celsius) for more than ten minutes during the first seven weeks of her pregnancy.
A lot of women ask about just taking a nice relaxing warm bath. In general, soaking in a warm, soothing bath is fine during pregnancy. Just make sure that the water temperature isn’t too high, for the reasons just mentioned.
Common sense suggests that after the first trimester, occasionally using hot tubs, saunas, and steam rooms for less than ten minutes is probably okay. However, remember to drink plenty of fluids to avoid dehydration. Later in the pregnancy, hot tubs and saunas are fine but limit your time to about 10 minutes.