New research from the University of Sydney suggests mums-to-be can safely exercise in warm weather, take spas and use saunas with minimal risk of heat stress to their unborn children.
The research, published today in the British Journal of Sports Medicine, contradicts public health advice that warns against exercise in warm weather or exposure to hot saunas or baths due to risks associated with a mother’s core temperature exceeding 39℃.
Senior author Associate Professor Ollie Jay said despite the clear health benefits of exercise during pregnancy few expectant mothers meet recommended activity levels and many report hot weather as a barrier.
“Studies show that many women are concerned about risks to their babies when exercising in the heat and that’s not surprising as the current public health advice is quite ambiguous,” said Associate Professor Jay, Director of the Thermal Ergonomics Laboratory in the Faculty of Health Sciences.
“While fetal heat balance is entirely dependent on the mother’s regulation of her own core body temperature, our research shows there are safe thresholds and to our knowledge for the first time provides clearer direction on physical activity and other heat-based activities during pregnancy.”
Irrespective of pregnancy stage, women can safely engage in:
- up to 35 minutes of very high-intensity aerobic exercise (at 80-90 percent of their maximum heart rate) at air temperature up to 25℃ with 45 percent relative humidity.
- water immersion (including aqua-aerobic exercise) in less than 33.4℃ for up to 45 minutes.
- sitting in hot baths (40℃) or hot/dry saunas (70℃; 15 percent relative humidity) for up to 20 minutes.
The findings are based on a review of all available evidence, encompassing a detailed analysis of 12 studies recording the core temperatures of 347 women exposed to heat stress through active exercise or through passive heating from spas or saunas.
The researchers found no study reporting core temperatures exceeding 39℃ nor a change in core temperature greater than 1.5°C during high-intensity exercise or passive heat stress.
The highest average core temperature was 38.3℃ for exercise on land, 37.5℃ for exercise in water, 36.9℃ for hot water bathing and 37.6℃ for sauna exposure.
The analysis also reports instances of reduction in the rise of core body temperature in women in the later stages of pregnancy, which suggests a woman’s ability to regulate core temperature may even be enhanced during pregnancy.
The researchers acknowledge there are some limitations to the review, namely the limited quantity and varying quality of existing research in this area, and state recommendations may change with further research.
“With growing summer temperatures worldwide and concerns around the link between women’s weight and pregnancy and birth complications, this research is an important step forward in improving knowledge in this area,” said Associate Professor Jay.
Pregnant women should discuss individual situations and requirements with their GP or obstetrician before engaging in exercise or activity in hot environments.
(Source: University of Sydney, British Journal of Sports Medicine)