Hot springs while pregnant: what ACOG, the CDC and the studies say
No official body has a rule for hot springs, so the hot tub guidance is the closest. A natural spring adds two things a hot tub does not have: water with no thermostat, and water nobody treats.
Short answer: Early in pregnancy, skip it. No official body has a rule written for hot springs, so the closest guidance is ACOG’s answer on saunas and hot tubs early in pregnancy: “It’s best not to.” The concern is raising your core temperature, which hot water does whether a heater or the ground warmed it. A natural spring adds two risks a hot tub does not have: no thermostat, and untreated water, where the CDC says to always keep your head above water. Later in pregnancy, ask your OB or midwife, and if they say yes, keep the water at 100°F or below and the soak short.
Hot springs feel different from a hot tub: a view, mineral water, a long drive to get there. Your body cannot tell the difference, though. Water above body temperature passes heat into you, and under water, sweat cannot evaporate to cool you down.
This guide sets out what the official sources say, what the pregnancy studies found, and what is specific to natural springs.
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 the official guidance says
None of the bodies below names hot springs. Their guidance is about hot tubs and saunas, which raise core temperature the same way a hot spring does.
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.”
The CDC. Its hot tub guidance says: “If you are pregnant, talk to a healthcare provider before using a hot tub.” For everyone, it gives 104°F (40°C) as the maximum water temperature.
The CPSC. The Consumer Product Safety Commission’s original hot tub warning gives the only number for pregnancy: “Pregnant women should stick to the 100-degree maximum rule.”
MotherToBaby. The teratology information service’s fact sheet on hyperthermia says: “Hot tub or sauna use during pregnancy should be limited.”
Why a hot spring is harder to control than a hot tub
A hot tub has a thermostat, even an imperfect one. A natural spring has whatever temperature the ground delivers.
Source water can be far hotter than any tub. At Hot Springs National Park in Arkansas, the National Park Service says the thermal water emerges at an average of 143°F (62°C). Developed resorts control the temperature of their pools; a primitive pool takes whatever the source delivers.
At Yellowstone, the park’s safety page describes boiling hot springs and ground that can be a thin crust over super-heated water, and it states plainly that swimming or soaking in hot springs there is prohibited.
So the CPSC’s 100°F rule only works if you can check it. Bring a thermometer, because nothing at a natural pool tells you the number. Our guide to US hot springs explains the difference between developed and primitive springs.
What the pregnancy studies found
The research is about hot tubs, saunas and fever, and it is observational, so it shows links rather than proof. The links cluster in early pregnancy.
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, and hot tubs had the strongest effect of any heat source the study looked at.
The National Birth Defects Prevention Study linked hot tub use in early pregnancy with gastroschisis and anencephaly, and a Kaiser Permanente study of 1,063 pregnant women found hot tub or whirlpool use after conception linked with twice the risk of miscarriage. Our guide to hot tubs in pregnancy covers these studies in full, including how small the absolute risks are.
How long it takes hot water to heat you
The risk is about core temperature, and that depends on water temperature and time. A 1981 study in the Canadian Medical Association Journal measured it in 20 women who were not pregnant.
- In water at 39.0°C (102.2°F), no woman reached a core temperature of 38.9°C (102°F) before 15 minutes.
- At 41.1°C (106°F), no woman reached it before 10 minutes.
- Most got out because they felt uncomfortable before their temperature got that high.
Those numbers assume you know the water temperature. At a natural spring you often do not, which is the strongest reason to check it and keep any soak short.
Untreated water: the rule for your head
Hot springs are natural warm fresh water, and a primitive pool is not chlorinated. The CDC says Naegleria fowleri, a rare ameba that causes a nearly always fatal brain infection, lives in warm freshwater lakes, rivers and hot springs, and infects people when water goes up the nose.
Its advice for hot springs is one line: “Always keep your head above water in hot springs.” You cannot get the infection by swallowing water, the CDC adds, and it is very rare, typically fewer than 10 cases a year in the US. Our guide to hot springs and the brain-eating amoeba covers the numbers and the precautions.
If your provider says yes later in pregnancy
These steps follow from the sources above.
- Choose a developed pool. Staff, controlled temperature and maintenance are what make the 100°F rule possible.
- Check the water yourself. Use a thermometer, and keep to 100°F or below, the CPSC’s maximum for pregnancy.
- Keep it short. In the 1981 study, water at 102°F took at least 15 minutes to raise core temperature to 102°F. A short soak in cooler water stays well inside that.
- Get out when you feel hot. Discomfort is the signal that made most women in that study get out early.
- Keep your head above water, as the CDC advises for every hot spring.
- Skip it with a fever, which already raises your core temperature, and skip alcohol, as the CDC advises for hot tubs.
If you soaked before you knew you were pregnant
This happens, and the right step is to tell your OB or midwife. The risks in the studies are small in absolute terms, and MotherToBaby 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 springs in pregnancy at a glance
| Question | What the sources say |
|---|---|
| Early pregnancy | ”It’s best not to” use a sauna or hot tub (ACOG); the study links are for early pregnancy |
| Any stage | Talk to a healthcare provider first (CDC, for hot tubs) |
| Water temperature | 100°F maximum in pregnancy (CPSC); 104°F maximum for everyone in a hot tub (CDC) |
| Source water | Averages 143°F at Hot Springs National Park (NPS); no thermostat at a natural pool |
| Your head | ”Always keep your head above water in hot springs” (CDC) |
| Yellowstone | Swimming or soaking in hot springs is prohibited (NPS) |
| Fever or alcohol | Skip the soak |
Questions to take to your OB or midwife
- Is a hot spring 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 soaked in a hot spring before I knew I was pregnant: which screening tests fit my timeline?
FAQ: hot springs and pregnancy
Can you go in a hot spring while pregnant? Not in early pregnancy. No official body has a hot-spring rule, but ACOG says it’s best not to use a sauna or hot tub early in pregnancy, and a hot spring heats you the same way. Later on, ask your provider first.
Is a hot spring safe in the first trimester? This is the time the studies flag. The links with neural tube defects and miscarriage were for heat exposure in early pregnancy, so skip the soak.
What temperature is safe in a hot spring when pregnant? The CPSC’s pregnancy rule for hot tubs is 100°F at most. At a natural spring, the only way to know is a thermometer, since source water can be far hotter: it averages 143°F at Hot Springs National Park.
Are hot springs safe in the third trimester? No official body gives a trimester rule for hot springs. The studies flag early pregnancy, and the CDC says to talk to a healthcare provider before using a hot tub at any stage, so that conversation comes first.
Can you get an infection from a hot spring while pregnant? Untreated hot springs can carry Naegleria fowleri, which infects through the nose. The CDC’s advice is to always keep your head above water in hot springs; infections are very rare, typically fewer than 10 a year in the US.
I soaked in a hot spring 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.
The bottom line on hot springs in pregnancy
A hot spring is a hot tub you cannot set. Early in pregnancy, the guidance on hot tubs and saunas says to stay out, and nothing about natural water changes that.
Later on, the decision belongs with your provider. If the answer is yes, a developed pool, a thermometer, 100°F or below, a short soak and your head above water keep both risks, heat and water, well in hand.