Pregnant women are usually advised to avoid excessive exposure to heat because of concerns it could harm their unborn child.
However, new research suggests that pregnant women can safely exercise in warm weather and take short hot baths or saunas without risks associated with exceeding a core body temperature of 39C.
The study, published in the British Journal of Sports Medicine, concludes that although the risk of heat stress is low, more work is needed to assess safe exposure for women who are physically active in hotter climates.
Guidelines
Women are encouraged to keep physically active during pregnancy to promote good health. However, expert guidelines from professional bodies, including the Royal College of Obstetricians and Gynaecologists, discourage the use of hot baths and saunas during pregnancy to protect against high heat and humidity.
Current guidelines do not clearly define critical heat stress limits that should be avoided. In an attempt to clarify these, an international team of researchers analysed how the body responds to heat in pregnancy and whether the body’s capacity for thermal regulation improves during pregnancy.
They analysed 12 studies which reported the core temperature response of 347 women at any stage of pregnancy to heat stress, either through exercise, or from the environment, such as saunas and hot baths.
They noted that none of the women in the studies exceeded the recommended core temperature limit of 39C.
· The highest individual core temperature reported was 38.9C
· The highest average core temperature was 38.3C for exercise on land and 37.5C for exercise in water
· The highest average core temperature was 36.9C for hot water bathing and 37.6C for sauna exposure
Safety Limits
Based on these results, the researchers calculate that pregnant women can safely engage in up to 35 minutes of high intensity aerobic exercise at air temperatures of up to 25C and 45% relative humidity.
They can also safely participate in aqua-aerobic exercise in water temperatures ranging from 28.8C to 33.4C for up to 45 minutes, and sit in hot baths at 40C or hot/dry saunas at 70C, with 15% relative humidity, for up to 20 minutes without reaching the recommended core temperature limit.
These limits can be applied at any stage of pregnancy, the researchers say.
The team also found a reduction in the rise in core temperature as pregnancy progresses, lending support to the theory that thermal regulation improves during pregnancy. They suggest this could be linked to changes in body mass and surface area.
‘Take Care’
Dr Virginia Beckett, consultant obstetrician and spokesperson for the Royal College of Obstetricians and Gynaecologists (RCOG), comments in an emailed statement: “Little research has been carried out into the effect of heat stress in pregnant women and the RCOG welcomes any new research in this area.
“The current NHS guidelines recommend avoiding the use of saunas, jacuzzis and steam rooms during pregnancy because of the risks of overheating, dehydration, and fainting – pregnant women are already at an increased risk of fainting due to hormonal changes.
“While this new study did not find a rise in core temperature of up to the recommended limit of 39C in 347 pregnant women exposed to heat stress, either through exercise or through passive heating, such as using a sauna or sitting in a hot bath, we continue to recommend that pregnant women follow NHS advice and take care when exercising and being in warm temperatures by drinking plenty of water before and after and not exhausting themselves.
“If women experience any unusual symptoms or feel unwell, they [should] stop exercising and contact a healthcare professional immediately.
“There are many health benefits to keeping active during pregnancy and we strongly encourage women to exercise while pregnant. Contact sports where there is a risk of being hit in the abdomen should be avoided and women with a medical condition, or who have not exercised before pregnancy, should seek advice from their doctor or midwife before exercising.”
SOURCES:
Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis, Ravanelli N et al, British Journal of Sports Medicine
Royal College of Obstetricians and Gynaecologists (RCOG)
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