Etiology of neural tube defect in man — Do teratogens play any part? Evidence from sex ratios

Abstract Neural tube defect (NTD) is more common among spontaneously aborted fetuses than in infants born in the third trimester, but there is no direct evidence that NTD-affected conceptuses, presenting at these two different gestational ages, are components of a single disease process. Evidence for homology is here presented in an analysis of the sex ratios of spontaneously and therapeutically aborted NTD-affected fetuses, and of sex ratios differing with variations in prevalence of NTD-affected infants. if it could be shown conclusively that NTD is a single disease process, with an inverse relationship between components expressed early and late in gestation, there would be implications for the ascertainment of families at risk for NTD, and for the search for environmental factors potentially involved in the causation of NTD.