Early diagnosis of fetal defects

The prevalence of anencephaly is about 1 in 1,000 births and the etiology for more than 90% of cases is unknown.

• The diagnosis of anencephaly during the second trimester of pregnancy is based on the demonstration of absent cranial vault and cerebral hemispheres.
• In the first trimester the diagnosis can be made after 11 weeks, when ossification of the skull normally occurs. There is progression from acrania to exencephaly and finally anencephaly.