Anencephaly is the most common of the severe birth defects and is caused by failure of closure of the anterior neural foramen and is the most severe type of neural tube defect, being four times more common in female than in male fetuses. Due to the absence of the cranial vault, the child has a frog-like appearance, a short neck, no brain, and only the base of the skull or part of the base of the skull can be seen, making it impossible for the child to survive. Anencephaly is mostly caused by insufficient folic acid supplementation during or before pregnancy, or by concomitant chromosomal or genetic anomalies. Occasionally, anencephaly is also caused by infection with a specific malformation-causing virus during pregnancy, which may pass through the placenta and lead to fetal developmental abnormalities, so chromosomal or genetic diagnosis is recommended for anencephalic babies after delivery.