Maternal hyperthermia as a possible cause of anencephaly.

Mothers of anencephalic infants were asked about febrile illness and sauna bathing during their pregnancies. In 7 of 63 affected pregnancies (11%), a history of maternal hyperthermia near the presumed time of anterior neural-groove closure was given. 5 had fever with a maximum recorded temperature ranging from 38.9 to 40.0 degrees C, each case being secondary to a different type of illness. The other 2 had possible hyperthermia episodes as a consequence of sauna bathing, with no infectious agent involved. The frequencies of hyperthermia at the same period of gestation in two control groups were 0% and 0.1%. This excess frequency of maternal hyperthermia at the period of anterior neural-groove closure, and the differing natures of its causes, imply that hyperthermia itself may be an aetiological factor in anencephaly.