Twin reversed-arterial-perfusion sequence is a serious complication of monozygotic multiple gestations, affecting 1 percent of monozygotic twins, or 1 in 35,000 births1. It has been hypothesized that in the presence of artery-to-artery and vein-to-vein anastomoses in a monozygotic placenta, blood is perfused by the hemodynamically advantaged twin (“pump” twin) to the other twin (“recipient” twin) by means of retrograde flow2. Inadequate perfusion of the recipient twin is responsible for the development of a characteristic and invariably lethal set of anomalies, including acardia and acephalus. Typically, the pump twin is structurally normal, but it is at risk for in.
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