Hot Tubs and Pregnancy Don't Mix

New research suggests that warnings against hot tub use during pregnancy have some basis in reality.

Women were twice as likely to suffer miscarriages if they took dips in hot tubs during the first 10 weeks of pregnancy, a survey of San Francisco-area women found.

The findings don't definitively link hot tub use to miscarriages. Instead, they only imply some sort of connection exists. However, study author Dr. De-Kun Li says that should be enough to keep newly pregnant women -- and those who wish to become pregnant -- out of hot tubs.

"It's a personal choice at this point, but why take the risk?" asks Li, an epidemiologist with the Kaiser Permanente Research Institute in Oakland, Calif.

Doctors have advised pregnant women against use of hot tubs and whirlpools for some time. But previous research hasn't provided enough information to give women with a firm recommendation about hot tub use, Li says.

Researchers do know, however, that high body temperatures caused by fever can lead to birth defects, especially those that prevent the skull or spinal cord from forming properly.

For the latest study, which will be published in the Nov. 15 issue of the American Journal of Epidemiology, Li and his colleagues turned to a 1996-1998 survey of 1,063 pregnant women from the San Francisco region.

About 10 percent of the women reported using hot tubs during the early months of their pregnancies. These women were more likely to be white, wealthy and college-educated than the others surveyed; they were also more likely to drink alcohol.

The women who used hot tubs more than once a week were 2.7 times more likely to suffer miscarriages than those who didn't use them; the miscarriage rate was two times greater among those who used hot tubs once a week.

Li acknowledges the study has limitations. It doesn't prove hot tub use causes miscarriages, but only suggests there may be a connection between the two. It's possible the researchers missed factors that could contribute to the miscarriage rate.

Also, the women in the study were not chosen randomly. They all decided to participate in the study, while hundreds more declined for a variety of reasons. As part of another research project, those who took part had to wear a meter that measured their exposure to magnetic fields.

The same survey, however, has already linked miscarriages to use of aspirin and painkillers, such as ibuprofen and naproxen, which are known as non-steroidal anti-inflammatory drugs.

However, it's clear high temperatures spell trouble for humans because the body loses control over its inner thermostat. Fetuses are especially vulnerable in the early weeks of life. They lack the ability to sweat and become more susceptible to the deadly effects of heat, Li says.

Hot tubs appear to pose special risks because they raise the body temperature of the mother without giving her body the chance to perspire into the air, he says. For that reason, saunas and steam baths may be less risky for the fetus because the mother can still sweat into the air, he adds.

For now, Li advises women to avoid hot tubs if they're in the first trimester of pregnancy or if they're hoping to become pregnant.

Frank Edward Myers III, an epidemiologist with Scripps Mercy Hospital in San Diego agrees with that advice. While the study is preliminary, it's well-designed, he says.

And he adds, "It probably isn't a bad idea to avoid hot tub use until more is known."

More information

Get some advice on hot tub use during pregnancy from the University of Michigan Health System or Discovery Health.

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