Hot Tubs, Saunas and Hot Baths in Pregnancy: Overheating Risks and Guidance

Urgent Guidance First

If you feel faint, dizzy, very hot or unwell in a hot tub, sauna or bath, get out, cool down and sit or lie down. If you have chest pain, trouble breathing, or you pass out, call 911 in the US. A person who faints while pregnant, especially after 28 weeks, is better placed on their side, according to the NHS (the UK health service). [1]

If you are pregnant, or might be, ask your own doctor or midwife about hot tubs and saunas before using them. This page is information only. It does not tell you what is safe for you, and it gives no water temperatures or times to follow.

What the Concern Is

The worry is overheating. A 2006 review by Christina Chambers described a limited number of human studies linking hot tub or spa use in early pregnancy to neural tube defects (problems in how the baby's spine and brain form) or miscarriage. [2] The same review noted that high maternal fever in early pregnancy has also been linked to neural tube defects. [2]

Animal research, the review says, points to the size, timing and length of a rise in core body temperature as the key factors, with a threshold of about 2 degrees C over baseline. [2] From this the author judged that hot tub or spa use raising core temperature to risky levels was "likely" possible, and that advice should cover limits on exposure. [2] That is an expert interpretation of limited human data. It is not a trial that measured harm from hot tubs directly.

What One Large Study Found

A US study of the National Birth Defects Prevention Study compared mothers of 10,825 infants with birth defects and 6,795 infants without. [3] Mothers of infants with gastroschisis (a defect of the abdominal wall) and anencephaly (a major neural tube defect) were significantly more likely to report any hot tub use in early pregnancy. [3] The authors also say they cannot exclude that some of the raised associations may be due to chance, because of many statistical tests and small numbers. [3]

This kind of study asks mothers to remember past exposure and cannot prove cause. We rate the evidence as limited and consistent with a possible risk, not proof.

Saunas: A Different and Older Source

A 2001 review of sauna bathing states that it does not influence fertility and is safe during the uncomplicated pregnancies of healthy women. [4] That sits uneasily beside the hot tub research above. The abstract does not give sauna temperatures or session lengths, the review is more than two decades old, and "uncomplicated pregnancy" is not the same as "any pregnancy". We label the sauna evidence mixed and limited. For the wider sauna evidence see the sauna evidence summary.

What Medical Bodies Say About Overheating

The American College of Obstetricians and Gynecologists advises avoiding becoming overheated while exercising in pregnancy, especially in the first trimester, and lists hot yoga or hot Pilates among activities that may cause overheating. [5] The NHS tells pregnant people to try to keep cool, and to stop if they feel uncomfortable, too hot or unwell. [6] Neither page we read gives a hot tub or sauna rule, so we do not make one up. Proper evidence not found for an official hot tub or sauna temperature limit in the sources we could read (NHS, ACOG, PubMed).

Warm Water That Is Not Hot

The NHS notes that swimming can be good exercise in pregnancy because the water can relieve pressure on muscles and joints, and that water-based pregnancy classes may exist. [6] Cooler, active water exercise and a very hot soak are different exposures. See water aerobics and aquatic exercise classes and water in pregnancy, labor and postpartum for birthing pools and labor baths, which follow separate rules.

Other Cautions in Pregnancy

• Fainting: heat is a listed cause of fainting, and so is standing up too quickly. [1] Getting out of hot water slowly matters more if you are dizzy. See fainting and low blood pressure after hot water.
• Alcohol with heat: a sauna review warns alcohol raises the risk of low blood pressure, irregular heartbeat and sudden death. [4] See alcohol, drugs and hydrotherapy.
• Health conditions: the NHS says that if you already have a health condition you may need to take extra care with exercise and can talk to your midwife. [6]
• Fever: if you have a fever, the Chambers review links high fever (not just hot tubs) to neural tube defects. [2] Ask your clinician about any fever in pregnancy.

Who Should Check First

Anyone who is pregnant, trying to conceive, or has not yet taken a pregnancy test and could be pregnant should ask a clinician before using a hot tub or sauna. People with a complicated pregnancy, high or low blood pressure, bleeding, or heart conditions should check first as well. Read hydrotherapy safety and therapies in pregnancy for broader cautions. Hydrotherapy is at most an extra comfort, never a substitute for prenatal care.