Use of Hot Tubs and Spas in Early Pregnancy Linked to Birth Defects
Women in the first month of pregnancy should stay out of hot tubs and spas to protect their fetuses from developing birth defects, physicians warned Tuesday.
Women who are exposed to such heat sources early in pregnancy have two to three times the normal risk of bearing a child with spina bifida or other so-called neural tube defects, according to a report in today’s Journal of the American Medical Assn. The finding appears to confirm earlier but unsubstantiated reports and anecdotal evidence.
In addition to using a hot tub, if the mother-to-be also runs a fever caused by an infection during the first month, the total risk can be as much as six times higher than normal, according to results of the largest study of birth defects so far undertaken.
In a separate study in the same journal, Swedish and American researchers have found that the risk of birth defects of all types is higher among women who put off childbearing until their 30s and 40s.
Although this increased risk in later pregnancies has long been recognized, physicians had previously thought it arose from the complications of childbirth that often occur in older women and that it could be minimized by proper medical care.
But the new study indicates that there is an additional risk, beyond that caused by complications such as diabetes and high blood pressure, arising from some as yet unidentified factor associated with aging.
The March of Dimes Birth Defects Foundation urged Tuesday that women follow the recommendation to avoid hot tubs and spas. “This study . . . is particularly important because women can improve their chances of having a healthy baby by avoiding exposure to excessive heat,” said Dr. Jennifer L. Howse, March of Dimes president.
Other public health authorities agreed that it would be prudent for pregnant women to avoid hot tubs and spas during early pregnancy, but noted that recent studies suggest that protection against spina bifida is now available. “Almost everybody agrees that small doses of folic acid before and during pregnancy can prevent (about two-thirds) of spina bifida cases,” said Dr. Godfrey Oakley of the U.S. Centers for Disease Control in Atlanta. Folic acid is one of the B vitamins.
And Dr. Barbara Crandell, a UCLA specialist in pediatric genetics, said that physicians should probably start recommending that women avoid the exposures.
Researchers have long known that exposure to heat in the early stages of pregnancy causes birth defects in animals, with the central nervous system being particularly vulnerable. The most common defect associated with it is spina bifida, which occurs when the bony casing around the spinal cord fails to close. Another is anencephaly, in which major parts of the brain and skull are missing.
Spina bifida usually results in mild to severe paralysis. Anencephaly results in stillbirth or death within hours or days of birth. Such defects occur in one or two births per 1,000.
But epidemiological studies of the risks of heat exposure conducted in humans during the 1970s were ambiguous, providing no strong evidence either supporting or negating the idea.
Dr. Aubrey Milunsky, a geneticist at the Boston University School of Medicine, decided to include such heat sources in a major study of birth defects involving nearly 23,500 women, primarily in New England, who were questioned during and after their pregnancies. Today’s report represents the first results from that study.
Milunsky and his colleagues at Boston University and Harvard Medical School found that the risk of neural tube defects increased nearly threefold for exposure to hot tubs, by nearly twofold for exposure to spas and by nearly twofold for fevers during the first month of pregnancy. If fevers were combined with exposure to hot tubs or spas, the risk increased sixfold.
They found no increased risk from the use of electric blankets, however.
Milunsky noted that further study will be needed to determine the effects of repeated exposures and varying water temperature. Carole Klein of the California Birth Defects Monitoring Program in Emeryville said that the agency is also conducting studies of the relationship between birth defects and heat exposure.
Milunsky noted that “a single study should not be used as the basis of a public health policy,” but said that it would be “prudent for women planning a pregnancy and continuing through the first two months to avoid hot tubs and saunas. . . . It’s a safe and harmless recommendation that could potentially do good.”
In the second study, Dr. Heinz W. Berendes, an epidemiologist at the National Institute of Child Health and Human Development, and Dr. Sven Cnattingius of the University Hospital in Uppsala, Sweden, studied the records of 173,715 Swedish women who gave birth to their first child between 1983 and 1987. They conducted the study there because Sweden has extensive health-care records and delayed childbearing is more common there than in the United States.
When they eliminated all birth defects associated with maternal complications, such as high blood pressure and diabetes, they found that the increased risk of birth defects for first childbirth above age 30 ranged from 40% to 100%. Because many of the problems involved late fetal death and gross retardation, Berendes speculated that the problem arises from an impairment of blood supply to the uterus and placenta in older women.
He also said that women should not be unduly concerned because “for the most part . . . women have a very low risk to begin with, so a 30% to 50% increase over a low risk is not a substantial increase. This is not so much a problem for individual women as it is a public health problem. As the population of older women having first babies increases, it will become a bigger problem.”
