title: Twinning and anencephalus occurrence in relation to fetus-fetus interaction.
abstract: The hypothesis proposed by Knox (1970) that an anencephalic fetus arises from a fetus-fetus interaction between two dizygous twins predicts that the twinning rate, the population incidence of anencephalus, and the female proportion of anencephalics in a population should be positively interrelated. These associations were tested using Canadian data during a long period of time and over a large geographical area. The results did not support the hypothesis.
mesh_terms: D000757:Anencephaly / Q000453:epidemiology / Q000209:etiology*; D002170:Canada; D004200:Diseases in Twins; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D011247:Pregnancy; D012737:Sex Factors; D014427:Twins; D014429:Twins, Dizygotic