How hot can a bath be during pregnancy?

What does the evidence say about bath temperature during pregnancy?

1. Typical bath water runs anywhere from about 93°F to 113°F, and a short, roughly 10-minute warm bath or shower has been shown to raise rectal temperature by only about half a degree Fahrenheit, well below the range of concern. 1
2. A hot tub running at its typical 104°F can raise a person's core body temperature to a level similar to temperatures shown to cause birth defects in animal studies, and long showers of 15 minutes or more were linked to a higher chance of gastroschisis in the same research. 1
3. MotherToBaby advises limiting hot tub or sauna use during pregnancy and taking precautions and limiting time in the heat when visiting a hot climate. 2
4. Researchers commonly categorize a concerning maternal temperature as 39°C (about 102°F) or higher, based on studies showing the threshold for heat-related harm in many species begins roughly 1.5°C above normal core body temperature; a large cohort study using this cutoff did not find an increased overall risk of congenital malformations from first-trimester fever, though it also didn't rule one out for specific defect types. 3
5. Research on pregnant athletes exercising vigorously found their core temperature stayed below the 39.0°C concern threshold even during high-intensity intervals, suggesting the body has real capacity to manage heat in pregnancy, which is part of why a brief, warm (not hot) bath is a different category of exposure than a long soak in very hot water. 4

Is bath temperature safe in each trimester?

• First trimester. This is the highest-stakes window, since neural tube closure happens in the first weeks of pregnancy and research links a maternal core temperature above about 39°C to a higher chance of neural tube defects.
• Second trimester. The same core-temperature caution continues, though the highest-risk window for neural tube defects has passed. Keep baths warm rather than hot and avoid lingering.
• Third trimester. Same guidance applies. A brief warm bath remains a fine way to unwind; save the hot tub setting for after delivery.