Sonography of nonconjoined monoamniotic twin pregnancies

Five nonconjoined monoamniotic twin pregnancies were identified prenatally by sonography. In all cases the diagnosis was made when umbilical cords of the two fetuses were seen to be entangled. One monoamniotic twin pregnancy was not recognized prenatally because the cords were not seen to be entangled. Although monoamniotic twins frequently die related to cord knotting, sonographic visualization of cord entanglement does not imply impending demise. Visualization of cord entanglement appears to be specific for the diagnosis of monoamnionicity, but the sensitivity is not known. Prenatal diagnosis allows informed planning of obstetrical monitoring and mode of delivery.