Expectant mothers often seek warm water immersion for relaxation and relief from muscle aches. However, during pregnancy, using a hot tub requires careful consideration of potential risks. The general medical consensus leans toward caution or outright avoidance of hot tubs, particularly in the initial stages of pregnancy. This recommendation is based on the body’s physiological response to prolonged exposure to high-temperature water.
The Primary Danger: Maternal Hyperthermia
The main concern with hot tub use during pregnancy is the risk of maternal hyperthermia, which is an abnormally high elevation of the mother’s core body temperature. A hot tub’s design creates an environment that rapidly transfers heat to the body faster than the body can dissipate it. Most hot tubs are factory-set to maintain water temperatures around \(104^\circ\text{F}\) (\(40^\circ\text{C}\)).
When immersed in water hotter than the body’s natural temperature, the normal cooling mechanism of sweating becomes ineffective. The circulating and re-circulated hot water prevents the evaporation of sweat, which is the body’s primary way to shed excess heat. Studies have shown that it can take as little as 10 to 20 minutes in water at \(104^\circ\text{F}\) to raise a pregnant person’s core temperature to an unsafe level. The goal is to keep the maternal core temperature below \(102.2^\circ\text{F}\) (\(39^\circ\text{C}\)), as temperatures at or above this threshold are associated with adverse outcomes.
Consequences of Elevated Core Body Temperature
An elevated maternal core body temperature carries risks to the developing embryo, especially during the first trimester. This time is known as organogenesis, the critical window when the baby’s major organs and central nervous system are forming. Exposure to excessive heat during this period has been linked to an increased incidence of neural tube defects (NTDs).
Neural tube defects are serious birth anomalies that affect the brain and spine, such as spina bifida and anencephaly. The risk of these defects is particularly sensitive to heat exposure before the sixth week of pregnancy, a time when a person may not yet realize they are pregnant. Research indicates that hot tub use in early pregnancy can nearly triple the likelihood of NTDs. Severe hyperthermia can also increase the risk of miscarriage, especially in the first trimester.
Defining Safe Temperature Limits and Exposure Time
For pregnant individuals, the maximum safe core body temperature is \(102.2^\circ\text{F}\) (\(39^\circ\text{C}\)). To prevent the core temperature from rising to this threshold, the American College of Obstetricians and Gynecologists (ACOG) and other health organizations recommend strict limits on water temperature and duration. The water temperature should not exceed \(100^\circ\text{F}\) (\(37.8^\circ\text{C}\)).
Even at the maximum recommended water temperature of \(100^\circ\text{F}\), exposure time must be limited to prevent a gradual rise in core temperature. The recommended limit for soaking is typically 10 to 20 minutes, with some sources advising no more than 10 minutes. Following these conservative water temperature and time limits is the most reliable way to maintain safety, as monitoring one’s actual core temperature outside of a clinical setting is impractical.
If a hot tub’s temperature cannot be accurately verified and set to \(100^\circ\text{F}\) or lower, it should be avoided entirely. Pregnant people should also exit immediately if they begin to feel uncomfortable, dizzy, or nauseous, as these are signs of overheating. Sitting with the arms and chest outside of the water may help to slow the heat transfer, but it does not eliminate the risk completely.
Understanding the Difference Between Hot Tubs, Baths, and Pools
Hot tubs are specifically designed to maintain a consistently high temperature through constant heating and recirculation, which is the mechanism that drives maternal hyperthermia. This high, sustained heat poses the primary danger.
Standard hot baths, in contrast, are generally much safer because the water begins to cool down immediately after the tap is turned off. A typical bath also allows much of the upper body to remain out of the water, which facilitates the body’s natural heat loss through evaporation.
A swimming pool presents no hyperthermia risk, as its temperature is significantly below body temperature and provides a cooling effect. Therefore, a warm bath or a swim in a cool pool are safe and relaxing alternatives for pregnant people seeking relief from discomfort.