Women in the first month of pregnancy should stay away from hot tubs and spas to protect their fetuses from developing birth defects, physicians warn.
Women who are exposed to such heat sources early in pregnancy have two to three times the normal risk of having a child with spina bifida or other neural tube defects, according to a report in today's s Journal of the American Medical Association. 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.
The March of Dimes Birth Defects Foundation urged yesterday 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 suggested 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.
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.
Dr. Aubrey Milunsky, a geneticist at the Boston University School of Medicine, thus 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.
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 child-bearing until their 30s and 40s.
Although this increased risk of 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, above and beyond that caused by such complications as diabetes and high blood pressure, arising from some as yet unidentified factor associated with aging.