Is it safe to use a sauna or jacuzzi (hot tub) in early pregnancy?

Safety of Sauna and Jacuzzi Use in Early Pregnancy

Pregnant women should avoid using saunas and hot tubs (jacuzzis) during early pregnancy due to the risk of maternal hyperthermia, which can potentially cause fetal harm.

Risks of Hyperthermia During Pregnancy

• Maternal hyperthermia (core temperature ≥39.0°C) during early pregnancy has been associated with potential teratogenic effects, particularly neural tube defects and other central nervous system abnormalities 1
• The first trimester is considered the most vulnerable period for heat exposure, as this is when critical fetal development occurs 2
• The critical factors that determine risk include:
  • Elevation of core maternal temperature at or above 2°C over baseline
  • Duration of exposure
  • Timing of exposure during pregnancy 1

Safety Guidelines for Heat Exposure

• The 2019 Canadian Guidelines for Physical Activity throughout Pregnancy explicitly recommend avoiding physical activity in excessive heat, especially with high humidity 3
• Hot yoga is specifically mentioned as an activity to avoid due to dehydration risk 3
• Pregnant women are advised to avoid activities that could lead to overheating as a general safety precaution 3

Research on Specific Heat Exposures

• Studies examining heat stress during pregnancy found that the highest individual core temperature reported across various heat exposures was 38.9°C, just below the proposed teratogenic threshold of 39.0°C 4
• For hot water bathing, the highest mean core temperature was 36.9°C (95% CI 36.8°C to 37.0°C) 4
• For sauna exposure, the highest mean core temperature was 37.6°C (95% CI 37.5°C to 37.7°C) 4

Time-Based Safety Thresholds

• Research suggests pregnant women might safely sit in:
  • Hot baths (40°C) for up to 20 minutes
  • Hot/dry saunas (70°C; 15% relative humidity) for up to 20 minutes 4
• However, one study found that some women reached a temperature of 38.9°C after just 15 minutes in a 39.0°C hot tub or 10 minutes in a 41.1°C hot tub 5
• Individual responses to heat exposure vary significantly, with some women experiencing discomfort and exiting heat environments before reaching concerning temperatures 5

Practical Recommendations

• If a pregnant woman chooses to use a hot tub despite recommendations:
  • Limit exposure to less than 10 minutes 5
  • Ensure water temperature is below 39.0°C 4
  • Monitor for signs of overheating (dizziness, faintness, excessive sweating) 3
  • Exit immediately if feeling unwell 3
• Swimming or water immersion exercise in temperature-controlled pools (≤33.4°C) is considered a safer alternative for up to 45 minutes 4

Common Pitfalls and Caveats

• Many pregnant women may not be aware of their pregnancy during the critical early weeks of the first trimester when heat exposure could be most harmful 2
• Hot tub and sauna temperatures can vary significantly from displayed readings, making it difficult to accurately assess exposure risk 1
• Individual factors such as hydration status, ambient temperature, and duration of exposure all influence how quickly core temperature rises 4
• The combination of pregnancy-related physiological changes and heat exposure may cause some women to feel uncomfortable before reaching dangerous core temperatures, providing a natural safety mechanism 5

Given the potential risks and limited benefits, it is prudent for pregnant women, especially in early pregnancy, to avoid saunas and hot tubs entirely rather than trying to use them within theoretical safety limits.