In utero twin-reversed arterial perfusion or TRAP sequenceTwin reversed arterial perfusion sequence, or TRAP sequence, is a very rare condition that occurs in monochorionic pregnancies, where more than one fetus share one placenta.

In TRAP sequence, one twin develops normally while the other lacks a working heart (acardiac) and/or other defined bodily features (head, limbs, etc.), which prevent the fetus from surviving on its own.

This imbalance causes the acardiac mass to draw all of its blood supply from the healthy, or “pump twin.” In order to sustain itself, the pump twin’s heart works extra hard to maintain its own blood supply as well as the blood flow to the acardiac mass.

This puts the healthy twin at risk for heart failure and even death if left untreated. And the larger the acardiac mass grows, the harder the pump twin works – causing a greater risk of heart failure. 

How Common Is TRAP Sequence?

TRAP sequence occurs in about 1 percent of monochorionic twin pregnancies and in about one in every 35,000 pregnancies overall.

What Happens During A TRAP Sequence Pregnancy?

Our fetal care team provides evaluations, information and support to help families make informed decisions about managing pregnancies complicated by birth defects like TRAP sequence.

Once diagnosed, doctors will closely monitor the stress levels and heart health of the pump twin and use ultrasound to watch the growth of the acardiac mass. If there are signs of heart failure early in your pregnancy, our team will discuss treatment options to increase the pump twin’s chances of survival.

Fetal intervention and early delivery are usually recommended to save the pump twin. However, not all TRAP sequence pregnancies require treatment. Normal delivery may be an option if the acardiac mass is small enough and the pump twin’s heart is healthy.

Microwave Ablation Treatment and Outcomes

In utero microwave ablation treatment to stop blood flow from the pump twin to the acardiac massOur center was the first in the world to offer microwave ablation to treat TRAP sequence. There are a number of surgical approaches to treating TRAP sequence and they all share the same goal of stopping blood flow from the pump twin to the acardiac mass. We’ll go over all our surgical methods in great detail during your consult. The most common procedures include fetoscopic cord occlusion, radiofrequency ablation and microwave ablation. 

The goal of microwave ablation is to increase the healthy twin’s chances of survival and normal development. The ultrasound-guided treatment is designed to seal off blood flow to the acardiac mass without harming the healthy fetus.

The procedure is done in the operating room with an epidural block.  A small needle-like device is inserted into the vessels of the acardiac mass. The microwave energy is used to create heat which seals the blood flow.

Microwave ablation to treat TRAP sequence has been 100 percent effective in immediately stopping blood flow in our small series of cases we’ve treated. While complications related to invasive procedures can occur, this quicker, less-invasive procedures are the safest for mother and baby.

Contact us

To learn more about TRAP sequence, or to refer a patient, call Charlotte Fetal Care Center at 877-899-2322.