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Acardiac / Trap Sequence

Acardiac / Trap Sequence Background

Acardiac twins also known as Twin Reversed-Arterial Perfusion (TRAP) sequence, is a rare and serious complication of monochorionic twins (twins that share the same placenta). Blood is pumped from one twin (“pump” twin) to the other twin (“acardiac” twin) by retrograde (backward) flow. Thus, the acardiac twin receives deoxygenated (oxygen depleted) arterial blood from the pump twin in the wrong direction.

The inadequate perfusion of the acardiac twin is responsible for a spectrum of potentially fatal anomalies including acardia (absent heart), acephalus (absent skull), and severe maldevelopment of the upper body. Although the pump twin is structurally normal, there is an increased risk of death (up to 50-75 percent) for that twin.

Because of the high risk of pregnancy loss in pregnancies complicated by Acardiac/TRAP sequence, surgical treatment in the womb to separate the circulatory systems of the twins is now a viable option.