Pregnant individuals are generally advised to avoid hot tubs. This common advice stems from concerns about how elevated body temperatures can affect both the expectant mother and the developing fetus.
Understanding the Core Danger
The primary concern with hot tub use during pregnancy is hyperthermia, an abnormally high core body temperature. Hot tubs, often set to temperatures around 104°F (40°C), can quickly raise a person’s core body temperature. It may take as little as 10 to 20 minutes in a hot tub for a pregnant person’s temperature to reach 102°F (38.9°C) or higher.
Unlike a regular bath where water cools over time and much of the body remains exposed to air, hot tubs maintain a constant high temperature through continuous circulation and reheating, making overheating more likely.
Swimming pools, on the other hand, are generally kept at much cooler temperatures, typically between 78°F and 86°F (25.5°C and 30°C), which does not pose a risk of hyperthermia. The sustained high temperature and full-body immersion in a hot tub contribute to a rapid and potentially dangerous increase in maternal core temperature.
Potential Health Risks
Hyperthermia can lead to several adverse health outcomes for the developing baby. Studies have shown an increased risk for birth defects, specifically neural tube defects (NTDs), in babies of women who experienced high temperatures early in pregnancy. These defects, such as spina bifida and anencephaly, occur when the spine or skull does not close properly during early development. The neural tube typically closes by the beginning of the sixth week of pregnancy, making the first trimester a particularly sensitive period for heat exposure.
Research indicates that exposure to heat sources like hot tubs in the first trimester is associated with an increased risk for NTDs. Women who reported hot tub use during the first two months of pregnancy were found to be 2.8 times more likely to have an infant with a neural tube defect than those with no heat exposure. Beyond neural tube defects, some studies suggest a possible small increased risk for other developmental issues, including certain heart defects, abdominal wall defects, or oral clefts when fever occurs in early pregnancy.
For the pregnant individual, overheating can lead to symptoms such as dizziness, lightheadedness, and fainting, which can increase the risk of falls. Dehydration can also occur due to excessive sweating in a hot environment. Some studies suggest an increased risk of miscarriage with hot tub use after conception, with one study observing a twofold increased risk.
Safer Options for Relaxation
For pregnant individuals seeking relaxation, there are several safer alternatives to hot tubs that do not carry the risk of hyperthermia. Warm baths are generally considered safe, provided the water is not excessively hot and the duration of the soak is limited. The water temperature in a bath should feel warm but not scalding, ideally around 98.6°F to 100°F (37°C to 37.8°C). Unlike hot tubs, bathwater typically cools down, reducing the risk of sustained overheating, and much of the upper body remains out of the water.
Swimming in a pool is another beneficial and safe activity during pregnancy. The buoyancy of the water provides relief from the added weight of pregnancy, easing pressure on joints and the back. Swimming helps maintain muscle tone, improves circulation, and can alleviate common pregnancy discomforts like swelling and sciatic pain. The cooler temperature of pool water also helps to keep the body from overheating, making it a suitable choice for exercise and relaxation throughout pregnancy.