- 1 in 1,000 at 12 weeks’ gestation.
- Absence of cranial vault and cerebral hemispheres.
- At 12 weeks acrania is suspected by absence of the normally ossified skull and distortion of the brain (exencephaly). At >16 weeks the brain is destroyed (anencephaly).
- Chromosomal defects in isolated acrania are rare.
- CNS or other defects are found in about 50% of cases, including spina bifida in 25%.
- Detailed ultrasound examination.
- If the pregnancy continues, follow-up should be standard.
- Standard obstetric care and delivery.
- Lethal condition with death within the first week of life.
- One previous affected sibling: 5%.
- Two previous affected siblings: 10%.
- Supplementation of the maternal diet with folate (5 mg/day) for 3 months before and 2 months after conception reduces the risk of recurrence by about 75%.