Early sonographic findings suggestive of the human fetal tail.

The prenatal diagnosis of a human tail was suggested in six fetuses with ultrasound findings of an echogenic protrusion in the lumbo-sacral region. All fetuses were at 14-16 weeks' gestation. The ultrasound findings disappeared in all cases at 22-23 weeks. Dermal abnormalities such as pilonidal sinus, deep dimples, and scarred tissue were found in all six newborns. It is possible that the late regression of the embryonic human tail was the cause of these dermal findings.