Monochorionic multiple pregnancy has a higher risk for obstetric complications, including those due to the development of twin-to-twin transfusion syndrome and reversed arterial perfusion syndrome (TRAP sequence). The latter occurs in 0.1% of all monochorionic pregnancies. The basis for TRAP sequence is a relationship between arterial and venous anastomoses from the appropriate placental areas, causing a recipient fetus to develop at the expense of a donor fetus. The presence of abnormal anastomoses is considered to be a main cause of acardia. The prognosis for a donor fetus is also unfavorable: the mortality rates in the absence of intrauterine correction are as high as 55%.