[Sirenomelia--a rare cause of an oligoanhydramnion in the second trimester--a case report].

Sirenomelia is a rare, but complex and lethal malformation. It is caused by a primary defect of the caudal axial skeleton and damage to the primary streak, which appears due to a vascular steal phenomenon. Sirenomelia appears sporadic with an incidence of 1-64,000 births. A risk for sirenomelia can be also found in patients with poorly controlled diabetes mellitus and in monocygotic twins. Leading ultrasound findings are fusioned lower extremities, bilateral renal agenesis, single umbilical artery and a distinct oligohydramnios. 3D ultrasound and color Doppler sonography can additionally be used for diagnostic, as well as amnioninfusion. There are 3 forms of sirenomelia, depending on missing or presence of the feet it is distinguished as sympus apus, monopus or dipus. We are presenting a case of sirenomelia with sympus dipus, which was transferred for further diagnostic of severe oligohydramnios in 21 weeks of gestation by the gynecologist.