Is Elevation Of Body Temperature Safe?

The do-gooders are out and at it again. A magazine aimed at the expectant mother and an Ontario Medical Association patient information newspaper advice pregnant women to avoid hot tubs, saunas and even hot baths because the heat could damage the developing fetus.

Both publications are distributed free to doctor’s offices for patients to browse at in the waiting room. When a pregnant woman I know read the first one, she got very upset. After reading the second, she began to cry. I don't know how many restless nights she spent trying to justify the real sauna suits she took.

Although she herself is a physician, until she read the articles, written by a prenatal teacher and a physician respectively, she wasn't aware that taking a sauna could be so hazardous to her unborn baby. That's because most authoritative sources believe that it is perfectly safe for a pregnant woman to take a sauna or use a hot tub.

Seventy years ago, a scientist reported that eggs incubated at temperatures of 39C to 43C, instead of the usual 37C, produced chickens with defects. Following this report, others showing that overheating pregnant rodents, sheep and monkeys could cause birth defects.

Although it is not scientifically valid to extrapolate the results of these artificially induced fevers in animals to humans that is precisely what some people did. The warnings should have ceased after editorials in the two major English medical journals were published in 1978. Obviously, they didn't, even though the prestigious British Medical Journal published another editorial in 1987 clearly indicating that a sauna is safe during pregnancy.

Being logical thinkers, you and I might well have asked, “Is it even possible to elevate a woman's body temperature in either a sauna or hot tub to the point where there is even a theoretical chance of it interfering with the development of a fetus?”

To find out, a group from the University of Washington took 20 non-pregnant women and put them in hot tubs with water temperatures of 39C and 41.1C and a sauna. A sensitive thermistor probe was inserted into their vaginas up near the cervix to actually measure the effects of the heat exposure.

They assumed, based on animal experiments, which a person's core temperature would have to go up at least 1.5 degrees C for any deleterious effect to occur. They thus set their threshold core body temperature to be 38.9C, which as any parent knows is really not very high. Most of the women exited the hot tubs when they became uncomfortable and that was before their core temperatures reached 38.9.

All of the women left the sauna before there was a significant body temperature elevation. The investigators concluded that it was safe for a pregnant woman to remain in a hot tub at 39C for at least 15 minutes and at 41.1C for at least 10 minutes. They suggested that these numbers were conservative and that most women could safely remain for 5 to 10 minutes more, particularly if the women were allowed to have their arms out of the water.