Two cases of a fetus with sirenomelia sequence.

We report two cases of a fetus with sirenomelia sequence which showed oligohydramnios and a single umbilical artery. The first case was of a single fetus with symelia apus and only one leg. Prenatal diagnosis of this case was possible. The second case was of a dichorionic-diamniotic twin pregnancy in which one fetus had symelia dipus with two fused lower extremities. Prenatal diagnosis of the condition was not made. In both cases, the fetuses died shortly after birth from respiratory distress due to severe pulmonary hypoplasia. Absence of urinary tract, imperforate anus, and spine deformity were confirmed in both cases. Although prenatal diagnosis of symelia dipus seems difficult, this condition must be considered in a fetus with severe oligohydramnios.