Intrauterine membranous cyst: a report of antenatal diagnosis and obstetric aspects in two cases.

A large, intrauterine membranous cyst originating from the subchorionic layer of the placenta was diagnosed by ultrasound in two pregnancies. The cyst was attached in both cases near the cord insertion. In one pregnancy this condition resulted in fetal growth retardation and diminution of umbilical circulation, but both of the deliveries were uncomplicated. This abnormality indicates careful monitoring of pregnancy and labor.