Twin Reversed Arterial Perfusion Syndrome: the Role of Ultrasound in Diagnosis and Management

Abstract

Acardiac twin pregnancies are a rare but severe complication of monochorionic twinning. This complication occurs in 1% of monozygotic twin pregnancies or 1 in 35 000 births. The anomaly arises due to superficial artery-to-artery placental anastomoses leading to reversed perfusion from the donor or pump twin to the acardiac twin. It is postulated that as a consequence of the hypoxic environment within the recipient fetus there is secondary atrophy of the heart and other organs. The acardiac twin has no chance of survival and it is kept alive by its structurally normal twin. The presence of the acardiac twin can adversely affect outcome in a number of ways. First, a growing parasitic mass can increase the cardiovascular demands on the pump twin leading to congestive heart failure and polyhydramnios. The continued growth of the acardiac twin can increase the intrauterine volume and this increased uterine mass effect may lead to preterm delivery. Finally, blood returning from the acardiac twin to the pump twin is deoxygenated which may lead to chronic hypoxia and growth restriction in the donor fetus. The perinatal mortality rate for the pump twin is approximately 50%. The twin reverse arterial perfusion sequence can be quite variable in its presentation and outcome. The role of ultrasonography is central to making the initial diagnosis, determining the prognosis, optimizing the time of intervention and follow up of treatment.