What is Twin Reversed Arterial Perfusion Sequence (TRAP) ?
Twin Reversed Arterial Perfusion Sequence (TRAP) occurs solely in monochorionic twin pregnancies. It is an extremely rare problem with an incidence of about 1 in 35,000 pregnancies and only about 1% of monochorionic twin pregnancies. In TRAP, there is one twin that has developed normally and the other that has severe anomalies. These anomalies include no upper body or heart, although it may have a lower body and legs. Because there is no heart (acardiac) in the one twin, the normal twin has to pump the blood both for itself and the other twin. The normal twin is therefore known as the "pump" twin. Reverse arterial perfusion describes that blood enters the acardiac twin through its umbilical artery and leaves the body via the umbilical vein, which is the 'reverse' of normal. Thus, the placenta is bypassed and the acardiac twin receives "used" blood from the "pump" twin.
There is an increased risk of death (50-75%) in the pump twin due it's having to pump blood (perfuse) to the acardiac twin as well as itself. This additional workload eventually puts a strain on the pump twin's heart that can result in heart failure. Additionally, because the heart is working so hard, there is increased blood flow to the kidneys, thereby leading to increased urine production and increased amniotic fluid (polyhydramnios). When polyhydramnios is present there is an increased risk of preterm labor and/or delivery.
Treatment Options
There are currently (2) management options available for pregnancies that result in TRAP:
Expectant Management
This is when your doctor closely watches your pregnancy with ultrasounds and timing your delivery to prevent the pump twin from dying while still in the womb. This is associated with a 50-75% risk of pregnancy loss, but usually only when the acardiac twin is large, generally considered to be greater than 50% of the size of the pump twin.
Radiofrequency Ablation
This involves stopping blood flow from the pump twin to the acardiac twin. This is a minimally invasive procedure that uses a very thin needle that is inserted into where the blood vessels enter the acardiac twin. The radiofrequency device then produces heat to seal the blood vessels. All of this is done with ultrasound guidance.
