Twin Reversed Arterial Perfusion Sequence

The maternal-fetal medicine specialists at University Hospitals diagnose and manage twin reversed arterial perfusion sequence (TRAP), also called acardiac twin gestation. This rare condition occurs in monochorionic twin pregnancies, in which the twins share a placenta. In TRAP, one twin’s heart supplies blood flow for both twins. This twin is called the “pumping twin” and has a normally developed cardiac system. The other twin, called the “acardiac twin” either lacks a heart or has one that is not fully formed. The extra work pumping blood for both fetuses can put the pumping twin at risk for cardiac failure.

How Do We Diagnose TRAP?

When an ultrasound is done, it is easy to confuse twin reversed arterial perfusion sequence with a monochorionic twin gestation in which one of the twins has died. However, our experts can diagnose TRAP using color and pulsed Doppler ultrasound. The umbilical arterial blood flow in a normal fetus is directed from the fetus to the placenta, whereas in the acardiac twin it is directed from the placenta (or from the umbilical cord of the normal twin). The umbilical vein that in the normal twin is directed from the placenta to the fetus, in the acardiac twin is directed from the fetus to the placenta.

Treatment of TRAP

At UH, we individualize management for TRAP sequence. Because the acardiac twin does not have properly developed cardiac system and other vital organs, they cannot survive outside the womb. Therefore, fetal interventions focus on monitoring the heart health of the pumping twin. If it is determined that they are at a greater risk for heart failure, procedures can be performed to stop blood flow to the acardiac twin.

The pregnancy can normally go to term if the acardiac twin does not grow much in-utero. If patients do not experience any further complications they can go on to have a normal, healthy delivery of the pumping twin.