Hot tub while pregnant: what ACOG, the CDC and the studies actually say
ACOG's answer for early pregnancy is that it's best not to, and the CDC says to talk to your provider first. Here is what the studies found, how long a soak takes to raise core temperature, and the CPSC's 100°F rule.
Short answer: Not in early pregnancy. ACOG’s answer to whether you can use a hot tub early in pregnancy is “It’s best not to,” because studies link it with birth defects, and the CDC says to talk to a healthcare provider before using a hot tub at any stage. The risk comes from raising your core temperature, so if your provider says yes later on, the Consumer Product Safety Commission’s rule for pregnancy is water no hotter than 100°F, and shorter is better.
Hot tubs get singled out in the pregnancy research, and the reason is simple. Water above body temperature passes heat into you, and under water, sweat cannot evaporate to cool you down.
This guide sets out what ACOG, the CDC, the Consumer Product Safety Commission (CPSC) and MotherToBaby say, what the main studies found, and how long it takes a soak to raise core temperature.
This is general information, not medical advice. Your OB or midwife knows your pregnancy, so take the questions at the end of this guide to them.
What ACOG, the CDC and the CPSC say
The official answers are short and point the same way.
ACOG. Asked “Can I use a sauna or hot tub early in pregnancy?”, the American College of Obstetricians and Gynecologists answers: “It’s best not to. Some studies suggest that using saunas and hot tubs early in pregnancy, especially for long periods of time, is associated with birth defects.” It adds that core body temperature rises in saunas and hot tubs, and that this rise can be harmful for the fetus.
The CDC. Its hot tub guidance has one line on pregnancy: “If you are pregnant, talk to a healthcare provider before using a hot tub.” For everyone, it says the water should not be hotter than 104°F (40°C).
MotherToBaby. The teratology information service’s fact sheet on hyperthermia says: “Hot tub or sauna use during pregnancy should be limited.”
The CPSC. Its original hot tub warning, released at the end of 1979, gives the only number: “Pregnant women should stick to the 100-degree maximum rule.” It warned that soaking in water above 102°F during the first three months could harm the baby, and that hot tub thermostats can be off by as much as four degrees, so it told users to check the water with an accurate thermometer first.
What the studies found
The evidence is observational, built on what women reported about their pregnancies, so it shows links rather than proof. The neural tube defect findings line up across studies, though, and the links cluster in early pregnancy.
Neural tube defects. A 1992 study in JAMA followed 23,491 women. Those who used a hot tub in early pregnancy had about 2.8 times the risk of a neural tube defect, after adjusting for age, folic acid supplements and family history, and hot tubs had the strongest effect of any single heat source the study looked at, saunas and fever included. A 2005 meta-analysis of 15 studies found that a raised body temperature in early pregnancy was linked with close to double the odds of a neural tube defect.
Other birth defects. The National Birth Defects Prevention Study compared 10,825 mothers of babies with birth defects with 6,795 mothers of babies without. Hot tub use in early pregnancy was linked with gastroschisis and anencephaly, and the odds of several defects were higher among women who used a hot tub more than once and stayed in for more than 30 minutes. The authors cautioned that, with many statistical tests and small numbers, some of these links may be due to chance.
Miscarriage. A Kaiser Permanente study of 1,063 pregnant women found hot tub or whirlpool use after conception linked with twice the risk of miscarriage, and the risk rose with more frequent use and with use in the first weeks. MotherToBaby notes that other studies have not found an increased chance, and that miscarriage has many causes.
How big is the risk?
Small in absolute terms, and avoidable. Neural tube defects are rare to begin with: the CDC estimates that about 1 in every 2,857 babies in the US is born with spina bifida, and about 1 in 4,762 with anencephaly.
A doubling of something that rare still leaves it uncommon, which fits MotherToBaby’s description: several studies have reported “a small chance” of neural tube defects in babies of people who had fevers or hyperthermia before the 6th week of pregnancy. Small is not zero, though, and staying out of the hot tub in those weeks costs nothing.
Why water temperature and time matter
The risk is about core temperature, not about hot tubs as such. A 2006 review by Chambers points to animal research showing that a core temperature 2°C or more above normal, and how early and how long it happens, are the critical factors. It advises keeping body temperature below 38.9°C (102°F), and warns that hot tub temperature readings vary, so the water temperature needs checking.
How long does a soak take to get there? A 1981 study in the Canadian Medical Association Journal measured it in 20 women who were not pregnant:
- In a hot tub at 39.0°C (102.2°F), no woman reached a core temperature of 38.9°C before 15 minutes.
- At 41.1°C (106°F), no woman reached it before 10 minutes.
- Most of the women got out because they felt uncomfortable before their temperature reached that level.
The authors concluded that usual hot tub use is unlikely to raise body temperature to a level that could harm a pregnancy, “although prolonged use may.” That is the reasoning behind the advice to keep any soak short and cooler, and it is also why ACOG singles out long periods of time.
If your provider says yes later in pregnancy
These steps come straight from the sources above.
- Check the water yourself. Use a thermometer rather than the dial, since the CPSC warns thermostats can be off by up to four degrees, and keep the water at 100°F or below, the CPSC’s maximum for pregnancy.
- Keep it short. In the 1981 study, even water at 102°F took at least 15 minutes to raise core temperature to 102°F. A short soak stays well inside that.
- Get out when you feel hot. Feeling uncomfortable was what made most women in that study get out, before their temperature got high. Treat it as the signal it is.
- Skip it with a fever. A fever already raises your core temperature, and MotherToBaby groups fevers with hyperthermia in its warning.
- No alcohol, as the CDC advises for everyone in a hot tub.
If you used a hot tub before you knew you were pregnant
This is common, and the right step is simply to tell your OB or midwife. The risks above are small in absolute terms, and the MotherToBaby fact sheet notes that prenatal ultrasound and an alpha-fetoprotein (AFP) blood test can screen for neural tube defects. Your provider can say which checks fit your timeline.
Hot tubs, saunas and baths
The 1992 JAMA study found the strongest link for hot tubs; for saunas the estimate was smaller and too uncertain to call. ACOG’s answer covers both, and our guide to saunas, cold plunges and massage in pregnancy covers the sauna side.
For the general temperature rules that apply to everyone, including the CPSC’s figures for healthy adults and children, see our guide to hot tub temperature. Our sauna vs hot tub comparison explains how differently the two heat you. Natural springs follow the same logic with less control over the water, which our guide to hot springs while pregnant covers, and if you are still trying to conceive, see our guide to saunas and hot tubs while trying to conceive.
Hot tubs in pregnancy at a glance
| Question | What the sources say |
|---|---|
| Early pregnancy | ”It’s best not to” (ACOG); the links to birth defects are for early pregnancy |
| Any stage | Talk to a healthcare provider first (CDC) |
| Water temperature | 100°F maximum in pregnancy (CPSC); 104°F maximum for everyone (CDC) |
| Time | Water at 102°F took at least 15 minutes to raise core temperature to 102°F in one study |
| Thermostat | Can be off by up to four degrees; check with a thermometer (CPSC) |
| Fever | Skip the hot tub; fever raises core temperature too (MotherToBaby) |
| Alcohol | None before or during (CDC) |
Questions to take to your OB or midwife
- Is a hot tub okay for me at this stage of pregnancy, and at what water temperature?
- How long is a reasonable soak, if any?
- Does anything in my pregnancy, such as blood pressure, make heat a bigger concern?
- I used a hot tub before I knew I was pregnant: which screening tests fit my timeline?
FAQ: hot tubs and pregnancy
Can you go in a hot tub while pregnant? Not in early pregnancy: ACOG says “It’s best not to,” and the CDC says to talk to a healthcare provider before using a hot tub at any stage. If your provider says yes later on, keep the water at 100°F or below and the soak short.
Is a hot tub safe in the first trimester? This is the time the studies flag. The links with neural tube defects and miscarriage were for use in early pregnancy, and ACOG advises against saunas and hot tubs early in pregnancy, especially for long periods.
What temperature is safe for a hot tub when pregnant? The CPSC’s rule is 100°F at most, below the 104°F limit the CDC gives for everyone. Check it with a thermometer, because the CPSC warns thermostats can be off by up to four degrees.
How long can I stay in a hot tub while pregnant? No official body gives a time. In a 1981 study, water at 102°F took at least 15 minutes to raise core temperature to 102°F, and water at 106°F at least 10 minutes, so a short soak in cooler water keeps a wide margin. Ask your provider first.
I used a hot tub before I knew I was pregnant. What should I do? Tell your OB or midwife. The absolute risk is small, and prenatal ultrasound and an AFP blood test can screen for neural tube defects.
Can a hot tub cause a miscarriage? One study of 1,063 women found hot tub use after conception linked with twice the risk, rising with more frequent and earlier use. Other studies have not found an increased chance, and miscarriage has many causes.
The bottom line on hot tubs in pregnancy
The sources agree on the shape of the answer. Early pregnancy is the time to stay out, because that is when the links with neural tube defects and miscarriage were found, and ACOG’s answer is that it’s best not to.
Later on, the question goes to your provider. If the answer is yes, the CPSC’s 100°F rule, a thermometer rather than the dial, a short soak and getting out when you feel hot keep your core temperature well away from the level the research worries about.