Twin Reversed Arterial Perfusion (TRAP)…

Twin reversed arterial perfusion (TRAP) sequence is a rare condition that occurs in identical twin pregnancies that share the same placenta (called a monochorionic pregnancy). One twin develops normally in the womb, while the other is severely malformed.

In the malformed twin, there is no heart or it has not fully formed. The head, upper body and other body parts may not be fully developed as well. TRAP sequence is very rare, occurring at random in approximately 1% of monochorionic twins.

What are the Symptoms and Complications with TRAP Sequence?

The twin developing normally can be affected by the backward blood flow occurring in TRAP sequence. The blood flows from the healthy twin baby (called the pump twin) to the twin without a heart (called the acardiac twin). Since the acardiac twin does not have a heart, the pump twin baby’s heart constantly pushes blood excessively to both the acardiac twin and the placenta.

This increased workload on the pump twin’s heart increases the risk of heart failure and excess amniotic fluid (called polyhydramnios). The larger the acardiac twin, the greater the workload that is placed on the pump twin’s heart which increases the potential for heart failure or death.

What Causes TRAP Sequence?

The exact cause is uncertain, but it is thought to occur very early in pregnancy from abnormal blood pressure or blood flow. This abnormal blood flow can significantly affect the development of one of the twin’s vital organs, including the heart and brain.

The acardiac twin has no heart, so it cannot pump blood. Therefore, the acardiac twin will not survive outside of the womb. The development of the acardiac twin will not improve and can affect the health of the other twin.

Pump Twin

TRAP sequence puts too much pressure on the heart of the “pump twin,” or the twin with the functioning heart. The increased demand can lead to heart failure in the normally developing twin.

Acardiac Twin

The acardiac twin has no beating heart, which does not help with blood flow to the placenta. The connections in the placenta and the “pump twin” support blood flow to continue to the acardiac twin.

Risk of TRAP Sequence

The diagnosis of TRAP sequence is reliant on the pressure exerted on the heart of the pump twin due to increased cardiac effort. If the acardiac twin has sufficient blood flow support from the pump twin, its body can grow at a similar pace to that of the pump twin. However, this can increase the risk of heart failure in the pump twin baby.

How is TRAP Sequence Diagnosed?

TRAP sequence is diagnosed during a prenatal ultrasound. It may be seen on an ultrasound as early as the first trimester. Patients with suspected or confirmed TRAP sequence may be evaluated at the Fetal Center. Using advanced imaging, more information may be obtained to make the diagnosis and assess the health of the pump twin. The highly skilled team within the Fetal Center will help you and your family navigate the diagnosis, treatment options and delivery.

How is TRAP Treated?

If the healthy pump twin is identified as having a higher likelihood of heart failure, a fetal surgery procedure may be advised to obstruct the blood vessels that supply the acardiac twin. Depending on how far along you are in your pregnancy, the procedure may be completed by Radiofrequency Ablation (RFA), bipolar coagulation or laser ablation. Whichever technique is used, the procedure to treat TRAP sequence is very similar.

The procedure will be done in the Riley Maternity Tower. During the procedure, you will be numb and depending on what type of anesthesia you get, you may be relaxed or drowsy. A scope with a camera is inserted through your abdomen into your uterus (womb) so the fetal interventionalist can see inside the womb. The instrument used will pass through this scope. Excess amniotic fluid may be drained if there is too much.

Delivering with TRAP

The procedure is minimally invasive, and complications from the procedure are rare. A normal delivery and future childbearing are not affected. Your fetal interventionalist will discuss any risks before the procedure. Most mothers will have a normal delivery and healthy baby with this pregnancy and future pregnancies.

Key Points to Remember

The larger the acardiac twin, the greater the workload that is placed on the pump twin’s heart which increases the potential for heart failure or death.
The exact cause is uncertain, but it is thought to occur very early in pregnancy from abnormal blood pressure or blood flow.
If it is determined that the healthy pump twin is at an increased risk for heart failure, fetal surgery may be recommended to close off the blood vessels feeding the acardiac twin.
The procedure is minimally invasive and complications from the procedure are rare. A normal delivery and future childbearing are not affected.