The sex ratios of anencephalics born to anencephalic-prone women.

Anencephalic infants born to women who are very prone to bear them do not have a sex ratio appreciably different from that of other anencephalic births. Moreover, the sexes of affected cases in sibships containing exactly two anencephalic births seem to be distributed approximately binomially. Bearing in mind the correlation between prevalence at birth and sex ratio in anencephaly, these findings suggest that an environmental teratogen attacks the fetuses of women who are already (perhaps genetically) disposed to bear anencephalic infants.