Mums-to-be can safely exercise in warm weather and even sit in a spa for short durations, a new study suggests.
A research review, published in the British Journal of Sports Medicine, found no evidence that exercising in temperatures up to 25 with 45 per cent relative humidity was harmful to mother and baby.
Researchers analysed 12 studies that looked at core temperature response of 347 pregnant women to heat stress, either through exercise or through passive heating, such as using a sauna or sitting in a hot bath.
Senior author Professor Ollie Jay, Director of the Thermal Ergonomics Laboratory in the Faculty of Health Sciences at Sydney University says not one study showed exercise in warm weather raised a woman's core body temperature above 39degC - which is considered harmful to the unborn baby.
The only women that got close to the threshold of 39degC were four very fit athletes who were running at a high intensity on a treadmill, said Professor Jay.
The highest individual core temperature reported was 38.9degC.
"In general people weren't even close to this 39 degrees Celsius threshold, suggesting that under the conditions that were tested the risk in terms of overheating and subsequently the baby overheating is very, very low," Prof Jay told AAP.
According to the findings, pregnant women can also sit in hot baths (at temperatures up to 40) or saunas for up to 20 minutes, with minimal risk of heat stress.
The researcher noted the data was limited and cautioned more research is needed.
"We are just making the conclusions based on the evidence that is currently available in the literature, so we can't say anything else about anything beyond that," Prof Jay said.
The findings contradict current guidelines for exercise during pregnancy advising against excessive physical activity when it's warm and humid to avoid heat stress.
Guidelines from the Royal Australian and New Zealand College of Obstetricians and Gynaecologists discourage pregnant women from using hot baths and saunas during pregnancy.
But given the clear health benefits of exercise during pregnancy, it's important to identify safe exposure and environmental limits for pregnant women who are physically active in hotter climates, said Prof Jay.
"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."
