Pregnant? Warm weather exercise and hot baths might be OK

Pregnant women who exercise outside onwarm days or spend a little time in a hot bath or sauna may notnecessarily raise their body temperature enough to causeproblems, a research review suggests.

While most women without health problems can safely exerciseduring pregnancy, doctors discourage workouts in hot weatherbecause it can lead to heat stress and dehydration. Physiciansalso advise women to avoid saunas and hot tubs because theseactivities can raise the body temperature and increase the riskof birth defects.

The risks of heat exposure from warm weather exercise,saunas and hot tubs are thought to develop when the internalbody temperature reaches at least 39 C, researchers note in the British Journal ofSports Medicine.

For the current study, researchers examined body temperaturedata from 12 previously published studies of 347 pregnant womenwho exercised outside during hot weather, took hot baths or usedsaunas or hot tubs. They found no evidence that any of theseactivities raised the body temperature to 39 C.

"Presumably people have been told to avoid exercise in hotweather and sauna and hot bath exposures because of concernsabout reaching this critical threshold," said senior studyauthor Ollie Jay of the University of Sydney in Australia.

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"It is very difficult to get that hot most people do notrealize that," Jay said in an email.

Across all of the smaller studies in the analysis, thehighest temperature reported for any woman was 38.9 C, and that was immediately after exercise. Warm weatherworkouts were also associated with the highest averagetemperature across all of the studies, at 38.3 C.

By comparison, the highest average temperature after a hotbath was 36.9 degrees,while the highest averagetemperature after time in a sauna was 37.6 degrees.

'Heaps of benefits' to exercise in pregnancy

Based on these results, the researchers conclude thatpregnant women can safely engage in up to 35 minutes of high-intensity aerobic exercise at outdoor temperatures of up to 25C.

These results also suggest that pregnant women may spend upto 20 minutes in a bath heated up to 40 degrees Cor a sauna heated to 70 degrees C, the authors write.

Beyond its small size, other limitations of the analysisinclude the varied designs and goals of the smaller studies itexamined, which made it difficult to rule out the possibilitythat some factors that were not measured might have impacted theresults, the authors note.

The study also wasn't a controlled experiment designed toprove whether saunas, hot baths or warm weather workouts aresafe for mothers or babies, or what duration or intensity ofactivity might be safest.

It istoo soon to change current recommendations againstthese activities for pregnant women, said Dr. Juma Rahman, aresearcher at the University of Auckland in New Zealand whowasn'tinvolved in the study.

Beyond heat stress, the risks can include less oxygenreaching the uterus and baby, Rahman said by email. Women withcertain medical conditions like anemia, carrying twins or otherobstetric complications may also have an increased risk ofheat-related health problems during pregnancy.

Still, pregnant women shouldn't avoid exercise. Among other things, it can help lower the risk of elevated blood pressure ordiabetes during pregnancy, help women avoid gaining too muchweight and strengthen abdominal and pelvic muscles.

"There are heaps of benefits," Rahman said.