Worldwide birth prevalence is approximately 1 per 2000 births. Anencephaly is lethal in all cases because of the severe brain malformation that is present. A significant proportion of all anencephaly cases are stillborn or are spontaneously aborted. Hispanic and non-Hispanic whites are affected more frequently than blacks. Anencephaly is readily apparent at birth because of the absence of the cranial vault and portions of the cerebrum and cerebellum.
Facial structures are generally present and appear relatively normal.
The cranial lesion is occasionally covered by skin, but, usually, it is not. Babies are frequently stillborn, and spontaneous abortion during pregnancy is common. Although the features of anencephaly are readily evident, physical examination for anomalies not related directly to the anencephaly is indicated to evaluate the possible need for cytogenetic studies. When additional malformations are present, there is an increased likelihood of cytogenetic abnormalities. The vast majority of isolated anencephaly cases are multifactorial in their inheritance pattern implicating multiple genes interacting with environmental agents and chance events.