Hot tubs are generally not recommended during pregnancy, especially in the first trimester. The core concern is heat: water at 104°F (the standard factory setting for most hot tubs) can raise your body temperature to levels associated with an increased risk of miscarriage and birth defects. That said, the risk depends on temperature, timing, and duration, so the picture is more nuanced than a blanket “never.”
Why Heat Is the Main Concern
The danger isn’t the water itself. It’s what happens to your core body temperature when you sit in it. The American College of Obstetricians and Gynecologists (ACOG) recommends that pregnant women keep their core temperature below 102.2°F. The Organization of Teratology Information Services sets an even more conservative threshold of 101°F.
Most hot tubs hold water at around 104°F. At that temperature, your body absorbs heat faster than it can shed it. Research published in the Canadian Medical Association Journal found that in a tub set to roughly 106°F, women’s core temperatures reached concerning levels in as little as 10 minutes. Even in a cooler tub (around 102°F), it took only 15 minutes to approach unsafe territory.
Pregnancy does change how your body handles heat. Your baseline temperature runs about 0.4 to 0.8 degrees higher than normal, and your body actually becomes better at cooling itself as pregnancy progresses, with increased sweating and blood flow to the skin. But in a hot tub, where you’re submerged and can’t cool through evaporation, those adaptations don’t help much.
Risks in Early Pregnancy
The first trimester is the highest-risk window. A study from the Kaiser Foundation Research Institute found that women who used a hot tub after conception had roughly double the risk of miscarriage compared to those who didn’t. That risk climbed with frequency: occasional use (less than once a week) carried a 70% increase, weekly use doubled the risk, and use more than once a week raised it by 170%. Women who started using a hot tub within the first four weeks after their last menstrual period faced the highest risk, with a 2.3-fold increase.
Elevated body temperature in early pregnancy has also been linked to neural tube defects like spina bifida. This connection has been studied primarily through maternal fever, but the mechanism is the same: sustained high core temperature during the critical weeks when the brain and spinal cord are forming (roughly weeks 3 through 6) can interfere with normal development. ACOG specifically notes that “exposure to heat from sources such as hot tubs, saunas, or fever has been associated with an increased risk of neural tube defects.”
Second and Third Trimester Risks
After the first trimester, the risk of neural tube defects from heat drops significantly because those structures have already formed. The miscarriage data also showed a weaker association when hot tub use began after four weeks of gestation. But overheating still carries risks later in pregnancy, including dizziness, dehydration, and drops in blood pressure that can reduce blood flow to the uterus. Your cardiovascular system is already working harder than usual, and prolonged heat exposure adds strain.
Infection Risks in Hot Tubs
Temperature isn’t the only issue. Hot tubs that aren’t properly maintained can harbor bacteria, viruses, and parasites. During pregnancy, your immune system is naturally suppressed to protect the fetus, which makes you more vulnerable to waterborne infections. Some of these pathogens can cross the placenta and directly affect the developing baby. Public hot tubs, hotel spas, and gym whirlpools are harder to trust because you can’t verify how recently the water was treated or how well the filtration system is working.
If You Still Want to Soak
Some women choose to use a hot tub briefly with precautions, particularly after the first trimester. If you do, the key variables are temperature, time, and body position. Keeping the water at or below 100°F significantly reduces the risk. Limiting your time to 10 minutes or less provides an additional margin. Sitting with your arms and upper chest above the waterline helps your body release heat. And getting out immediately if you feel flushed, sweaty, or lightheaded is essential.
A warm bath is a much safer alternative. Water set between 98.6°F and 100°F won’t raise your core temperature to dangerous levels. A 2019 review of evidence found that baths up to 104°F stayed within safe limits for up to 20 minutes, but keeping the water closer to body temperature gives you the most room for comfort without worry. Unlike a hot tub, a bath also cools over time, which works in your favor.
How This Compares to Exercise
You might wonder why exercise in warm weather gets a pass while hot tubs don’t. The difference is how your body cools itself. During exercise, sweating pulls heat away from your skin effectively. Studies of pregnant women exercising at a self-selected pace in controlled environments found that core temperatures rose less than 1.5°F over 30 minutes, staying well within safe range. In a hot tub, you’re surrounded by water that’s hotter than your body. Sweating can’t evaporate, and there’s no effective way to shed heat. Your temperature climbs passively whether you feel it or not.
Practical Takeaways
- First trimester: Avoid hot tubs entirely. The combination of miscarriage risk and neural tube defect risk makes this the clearest call.
- Later trimesters: Brief soaks in water below 100°F carry less risk, but standard hot tub temperatures (104°F) are still too high.
- Time limits: If you do get in, stay under 10 minutes and keep your upper body out of the water.
- Warm baths: Water between 98.6°F and 100°F is a safe and comfortable option throughout pregnancy.
- Public hot tubs: Carry additional infection risks due to uncertain maintenance, so private, well-maintained tubs are preferable if you choose to soak at all.