Possible Teratogenic Hyperthermia and Marathon Running

Abstract

To the Editor.— The article by John D. Cantwell, MD (240:1409, 1978), extolled the many benefits of running. I would like to add a note of caution for women runners; namely, that marathon running may pose a teratogenic risk during early pregnancy. This warning seems warranted on the basis of the following evidence: First, marathon runners experience sustained increases of core temperature into the "high fever" range.^1,2Second, recent studies^3-5have shown an association between birth defects and episodes of maternal hyperthermia. Because the first half of gestation is apparently the period of greatest risk for hyperthermia-induced birth defects,⁴a substantial number of women may already have trained for and run the marathon during this critical period, either because they were unaware of or unhindered by their pregnancy. A study of the outcomes of such pregnancies might be informative in regard to the relationship between high maternal