Good news for the pregnant ladies amongst us!
Pregnant women have long been told to avoid extremes of heat, and have been limited to measures such as limiting baths to body temperature (37°C), or not exercising at high intensities for prolonged periods. The aim of this has been to keep their core body temperature below 39°C, which is the level thought to potentially cause harm to their unborn babies.
If you’d like to read more about the benefits of exercising while pregnant, we’ve written another post about it here.
According to a recent article published in the British Journal of Sports Medicine, these guidelines are overly strict, and women and their unborn children can actually sustain significantly higher temperatures than we once thought.
The guidelines suggested by this article are that pregnant women can safely engage in:
1. Exercise for up to 35 min at 80–90% of their maximum heart rate, at a temperature of 25°C and relative humidity of 45%. Put simply, this is the humidity level at which people tend to feel most comfortable.
2. Exercising in water at or below 33.4°C for up to 45 min.
Most swimming pools are somewhere in the range of 27-29°C, well below the recommended threshold.
3. Sitting in hot baths (40°C) or hot/dry saunas (70°C; 15% relative humidity) for up to 20 min, irrespective of pregnancy stage.
The authors also noted that in the 347 women studied, not one of them recorded a core body temperature high enough to cause harm to their unborn child, regardless of what type or intensity of exercise they were doing, or what type of environment they were in.
However, Obstetricians are still emphasising that it is probably still not recommended to exercise for longer than 60 minutes at a time, or spend “prolonged” time in spas and hydrotherapy pools, as these are often heated to at or above 32°C.
Despite these guidelines, it is obvious that pregnant women should use a common sense approach.
They need to listen to their bodies and remove themselves from the situation if they begin to feel uncomfortable.
I would’ve loved to hear these new guidelines during my first pregnancy.
I can recall being quite uncomfortable in the final weeks, and longing to have a long hot bath. However, I diligently set the water temperature to 37°C, and was sadly disappointed at the comfort that bath offered. It probably took longer to run than the time I actually spent in it, before it got too cold. Setting the temperature a degree or two higher would’ve been bliss!!!
Does this information change how you feel about exercise, pools, or saunas in pregnancy?
I’d love to hear your thoughts.
 Ravanelli N, Casasola W, English T, et al
Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis
Br J Sports Med Published Online First: 01 March 2018. doi:10.1136/bjsports-2017-097914