Fetal Therapy Phone: (323) 361-6074 or (800) 687-2229
Fetal Therapy Web: www.maternal-fetalhealth.com

Acardiac / Trap Sequence Background

Acardiac twins also known as Twin Reversed-Arterial Perfusion (TRAP) sequence, is a rare and serious complication of monochorionic twins. Blood
is perfused 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 lethal 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.

Risk factors associated with pregnancy loss include polyhydramnios (defined as a maximum vertical pocket of amniotic fluid greater than or equal to 8.0
centimeters), large TRAP twin (estimated fetal weight of the acardiac twin is 50 percent or greater than that of the pump twin), evidence of heart failure in the pump twin (hydrops), or critically abnormal blood flow patterns.

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

Acardiac / Trap Sequence Treatment

Operative fetoscopic directed umbilical cord occlusion of the acardiac fetus is offered to those patients who meet specific surgical criteria (listed above). It is important to understand that a single surgical approach is inadequate to provide optimal treatment. Each pregnancy must be individually assessed, and the type of fetal surgery must be tailored to the specifics of each case.

Note that all surgeries are performed under local anesthesia with intravenous sedation. About a 2 to 3 millimeter (one tenth of an inch) incision is placed on the maternal abdomen to allow the insertion of the microsurgical instruments into the womb.