Swimming is a highly recommended low-impact exercise during pregnancy, offering benefits like buoyancy to relieve joint pressure and reduce swelling. Heated pools are generally considered safe for swimming while pregnant, but this safety depends entirely on maintaining a strict temperature threshold. The primary concern is not the act of swimming itself, but the risk of raising the core body temperature too high due to external heat.
The Core Danger: Maternal Hyperthermia
The main risk associated with overly warm water environments is maternal hyperthermia, an elevation of the pregnant woman’s core body temperature. Experts consider a prolonged core temperature above 101°F (38.3°C) to be a potential concern for the developing fetus. The body’s natural temperature regulation systems are already working harder during pregnancy, making it easier to overheat when exposed to external heat.
This risk is especially pronounced during the first trimester, a period when the fetus’s major organs and systems are rapidly forming. Exposure to high heat during this early stage has been linked to an increased risk of neural tube defects (NTDs). NTDs are serious abnormalities of the brain or spinal cord, such as spina bifida or anencephaly, which occur when the neural tube does not close properly.
Because the neural tube closure occurs extremely early in pregnancy, often before a woman knows she is pregnant, avoiding prolonged exposure to environments that cause core body temperature to rise is important from conception onward. Unlike heat generated by exercise, which the body can usually regulate by moving blood to the skin’s surface and sweating, heat from an external source like a hot pool can prevent the body from effectively cooling itself.
Safe Temperature Guidelines for Swimming
The generally accepted maximum safe water temperature for a pregnant woman to exercise in is 92.1°F (33.4°C). A temperature range between 80°F and 90°F (27°C and 32°C) is ideal for swimming and aquatic exercise.
A review of studies concluded that pregnant people could safely exercise in water for up to 45 minutes when the temperature remained below 92.1°F (33.4°C). This lower temperature range helps ensure that the woman’s body can dissipate the heat generated by the exercise without increasing her core temperature to unsafe levels. If the pool temperature is near the upper limit, it is important to limit the duration of the swim and stay attentive to any signs of overheating.
It is advisable to check the posted temperature or ask staff before entering a heated pool. Maintaining hydration by drinking plenty of water and being cautious of slippery pool decks are practical steps to ensure a safe experience. If the water feels uncomfortably warm, even if it is within the recommended range, exit the pool.
Hot Tubs, Spas, and Saunas
Hot tubs and spas are smaller, higher-temperature soaking environments, typically maintained at 100°F to 104°F (38°C to 40°C). This is significantly higher than the safe limit for pregnant women, and soaking in water this warm can quickly raise the core body temperature above the 101°F threshold, potentially within ten to twenty minutes. Because of the high, consistent heat and the difficulty the body has in regulating its temperature while immersed, hot tubs and spas are strongly discouraged throughout pregnancy. The risk of overheating is compounded by a drop in blood pressure that can lead to dizziness or fainting when exiting the tub.
Saunas and steam rooms pose a similar threat, even though they are dry or humid heat environments rather than water immersion. These environments also cause a rapid rise in core body temperature and can lead to significant dehydration. Dehydration can be a serious concern during pregnancy and can interfere with the placenta’s function.