Anencephaly is associated with spina bifida, facial and nasal clefts, omphalocele and polyhydramnios. Because of the polyhydramnios , increased fetal movement can be seen. The differential diagnosis includes amniotic band syndrome and large encephaloceles. In amniotic band syndrome, early amnion rupture occurs with absence or disruption of the cranial vault. The defect is usually asymmetric and associated with abnormality or amputation of other body parts and occasionally with oligohydramnios.
Large encephaloceles can mimic anencephaly, but generally have more calvarial development.
Anencephaly occurs in about 1 in 1000 births. Multifactorial inheritance with both genetic and environmental factors is implicated. Recurrence risk after one affected pregnancy is two to three percent for any open neural tube defect. Screening with maternal serum alpha-fetoprotein screening will detect most cases of anencephaly. Pregnancy termination is offered at any gestational age.