Complications in monochorionic twin pregnancies

Monochorionic placentas occur in two-thirds of identical (monozygotic) twin pregnancies and typically feature inter-fetal vascular anastomoses on their surface. These anastomoses can cause very specific complications including twin-to-twin transfusion syndrome (TTTS) in about 10 %, TAPS in 5 %, twin reversed arterial perfusion (TRAP) sequence in 2.5 % and spontaneous intrauterine fetal death (IUFD) in 2 % of monochorionic-diamniotic twin pregnancies. Moreover, unequal sharing of placental territories can lead to selective fetal growth restriction (sFGR) in about 15 %. Monochorionic multiples affected by such complications are at increased risk of mortality, brain abnormalities and neurodevelopmental disorders. This narrative review provides insight into prenatal detection and management of specific complications of monochorionic twin pregnancies.