Aversion to hot baths traces back to data from the American College of Obstetricians and Gynecologists (ACOG) on the effects of raised body temperature on the development of a fetus, especially during the first trimester.
When a mother has a fever higher than 102.2 degrees F, it can cause a drop in heart rate, which
... decreases oxygen to the fetus. Bouts of high body temperature due to fever or from external sources can also increase the risk of miscarriage during the first six weeks of pregnancy.
The main goal is to avoid raising your core temperature, says CNN’s Dr. Sanjay Gupta. A hot bath, if not uncomfortable and scalding, is probably just fine. But hot tubs and saunas are best avoided.
Women who live in hot climates should take care not to overheat — stay indoors in air-conditioning, if the temperature spikes outside. As for women who want to continue exercising during pregnancy? Gupta says:
In general, exercising during pregnancy is very dependent on each individual. Some people are able to continue their usual level of activity throughout most if not all of their pregnancy, while others are sensitive to any exertion that raises their heart rate. Keep in mind that if you experience symptoms such as lightheadedness, fainting, a rapid heart rate that doesn't slow back down or dehydration — no matter how gentle your activities may be or how great shape you are in — it's important to rest and contact your doctor or midwife if needed. Above all else, listen to your body while exercising both during your pregnancy and beyond.
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