Prenatal diagnosis of sirenomelia in the first trimester: A case report.

Sirenomelia or "mermaid syndrome" is a rare congenital syndrome characterized by the anomalous development of the caudal region of the body. We present a case of sirenomelia diagnosed in the first trimester using two-dimensional and three-dimensional ultrasonographic examination. A nulliparous woman aged thirty years was referred to our perinatology unit for evaluation because of oligohydramnios at 12 weeks of gestation. Her medical history was unremarkable. There was no family history of genetic abnormalities. We identified a single lower extremity and severe oligohydramnios, which are characteristics of sirenomelia. Sirenomelia, a developmental defect involving the caudal region of the body, is associated with several internal visceral anomalies. Sirenomelia is fatal in most cases due to the characteristic pulmonary hypoplasia and renal agenesia. Prenatal diagnosis of sirenomelia may be difficult in the second or third trimester because of the severe oligohydramnios; it should be easier to diagnose sirenomelia in the first trimester.