Hot Baths During Pregnancy: Safety Guidelines
Hot baths are safe during pregnancy if you limit exposure to less than 10 minutes, keep water temperature below 39.0°C (102.2°F), and exit immediately if feeling unwell. 1
Temperature Thresholds and Timing Limits
The critical concern with hot baths during pregnancy is maternal hyperthermia—defined as core body temperature ≥39.0°C—which poses teratogenic risk, particularly for neural tube defects when exposure occurs during early pregnancy. 2, 3
Specific safe exposure limits based on research:
- Hot water bathing at 40°C: Safe for up to 20 minutes without exceeding the teratogenic threshold 3
- Hot tubs at 39.0°C: Body temperature unlikely to reach 38.9°C before 15 minutes of immersion 4
- Hot tubs at 41.1°C: Body temperature unlikely to reach 38.9°C before 10 minutes of immersion 4
- Maximum safe core temperature: Must remain below 38.9°C 2, 3
The highest mean core temperature recorded after hot water bathing in pregnant women was 36.9°C (95% CI 36.8°C to 37.0°C)—well below the teratogenic threshold. 3
Practical Safety Recommendations
To minimize risk while bathing: 1
- Keep water temperature below 39.0°C (verify with thermometer, as hot tub/spa temperature readings can be variable) 2
- Limit immersion to less than 10 minutes 1
- Exit immediately if experiencing discomfort, dizziness, nausea, or feeling unwell 1
- Avoid hot yoga or heated environments with high humidity that impair heat dissipation 1
Critical Timing Considerations
First trimester carries highest risk: Animal studies consistently demonstrate that heat exposure is most hazardous during the first trimester when organogenesis occurs, particularly for CNS abnormalities. 5 Women who may not yet be aware of pregnancy should be especially cautious about prolonged heat exposure. 2
When Hot Baths Should Be Avoided
Avoid hot baths entirely if you have: 6
- Active cholestasis-associated pruritus (hot baths/showers can worsen itching) 6
- Any signs of pregnancy complications requiring immediate medical attention 1
Evidence Quality and Nuances
The guideline recommendation from the 2019 Canadian physical activity guidelines 1 is based on converging evidence from multiple sources. While human studies directly linking hot tub use to birth defects are limited 2, the recommendation errs on the side of caution given: (1) established association between high maternal fever and neural tube defects in humans, and (2) extensive animal literature demonstrating that elevated core temperature ≥2°C above baseline is the critical teratogenic factor, regardless of heat source. 2
Important caveat: Most women naturally exit hot water due to discomfort before reaching dangerous core temperatures. 4 In one study of nonpregnant women, many left the hot tub in discomfort before their body temperature reached 38.9°C. 4 This built-in safety mechanism provides additional protection, but should not be relied upon as the sole safeguard.
Therapeutic Use During Labor
During active labor (not pregnancy maintenance): Warm tub baths at comfortable temperatures have been used safely during first stage labor, with one study showing women bathed for 30 minutes to 2 hours without adverse maternal or neonatal outcomes. 7 However, this applies specifically to labor management, not routine pregnancy bathing.