Ultrasonographic prenatal diagnosis of the 13q-syndrome.

A case is presented in which ultrasonographic examination led to the prenatal detection of a ring 13 chromosome in a fetus. At 18 weeks' gestation, the fetus presented with holoprosencephaly, an abnormal configuration of the lower extremities, and an atrial septal defect. Although the amount of amniotic fluid was normal, limb movements were never observed throughout pregnancy. The lower extremities were always flexed at the knee and talipes equinovarus was present. Hydrocephaly became apparent during the 2nd trimester. The ultrasonographic findings were confirmed by postpartum autopsy and X-ray examination. The ring chromosome was identified through amniocentesis and later verified in postpartum tissue.