A monoamniotic pregnancy is the least common type of monozygotic (identical) twin pregnancy, occurring when the twins share both a single placenta and a single amniotic sac. This is the highest-risk type of multiple gestation because the fetuses are in direct contact, which increases the risk of cord entanglement, where the umbilical cords become twisted around one another, potentially cutting off blood flow. On prenatal ultrasound, monoamniotic twins are identified by the absence of any intertwin membrane separating the amniotic sacs. These pregnancies require very close monitoring throughout gestation and careful consideration of delivery timing to minimize the risk of in-utero death from cord accidents.
Sonography Term