BACKGROUND AND PURPOSE:

• Animal model evidence and retrospective studies in humans have demonstrated increased risk of fetal malformations in the setting of severe hyperthermia (primarily related to fever)
• Maternal core temperature exceeding 39.0°C (or an elevation of ~1.5°C to 2.0°C from baseline) has been suggested as the critical threshold to avoid additional risk of birth defects, especially neural tube defects
• ACOG, RANZCOG and RCOG discourage prenatal use of hot tubs and saunas and to avoid heat and humidity during pregnancy
• Exercise during pregnancy is recommended, however
  • Concern that more intensive exercise may result in increased maternal core temperature
  • Alternatively, thermoregulation may keep core temperature below a critical level
• Ravanelli et al. (British Journal of Sports Medicine, 2018) examined whether exercise and passive heat stress can negatively impact pregnancy by elevating core temperature to a critical level beyond 39.0°C

METHODS:

• Systematic review and meta-analysis
• Studies were included that reported the core temperature response of pregnant women
• The critical core temperature for teratogenicity risk was defined as ≥39.0°C
• The core temperature was measured during any period of gestation in response to exercise or passive heat stress

RESULTS:

• Data was pooled from 12 studies, for a total of 347 subjects
• There were no reports of any core temperature exceeding the recommended maternal threshold of 39.0°C
  • Overall, 38.9°C was the highest reported individual core temperature
• The highest mean end-trial core temperature was
  • 38.3°C (95% CI 37.7°C to 38.9°C) for land-based exercise
  • 37.5°C (95% CI 37.3°C to 37.7°C) for water immersion exercise
  • 36.9°C (95% CI 36.8°C to 37.0°C) for hot water bathing
  • 37.6°C (95% CI 37.5°C to 37.7°C) for sauna exposure

CONCLUSION:

• This study suggests that pregnant women at any gestational stage can safely engage in
  • Exercise for up to 35 min at 80%–90% of their maximum heart rate in 25°C temperature and 45% relative humidity
  • Water immersion (≤33.4°C) exercise for up to 45 min
  • Sitting in hot baths (40°C) or hot/dry saunas (70°C; 15% relative humidity) for up to 20 min

Learn More – Primary Sources:

Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis

Related ObG Topics:

Does Exercise in Pregnancy Decrease Risk of Gestational Diabetes?

Does Exercise During Pregnancy Impact Hypertension or Macrosomia?