What is twin reversed arterial perfusion (TRAP) sequence?

Twin reversed arterial perfusion (TRAP) sequence is a rare anomaly that occurs in pregnancies where identical twins share the same placenta (the organ that nourishes the fetus in the womb). It happens in about 1 in 35,000 births.

In TRAP sequence, one of the twins is missing a heart (acardiac) or a head (acephalic) and the other twin develops normally. In the womb, the acardiac/acephalic twin gets blood from the normal twin (also known as the “pump” twin).

The reason it’s called “reversed perfusion” is that blood comes to the acardiac/acephalic twin through its umbilical artery and leaves through the umbilical vein. This is the opposite of how a fetus normally receives blood.

Unfortunately, because the acardiac/acephalic twin does not develop properly, it has no chance of survival and may die prior to birth. This can be dangerous for the surviving twin.

Heart failure for the pump twin is a major concern. That’s because the acardiac/acephalic twin puts a lot of pressure on the pump twin for blood. If left untreated, the pump twin has only a 30 to 50 percent chance of surviving. In addition, the risk of the pump twin dying increases if the acardiac/acephalic twin grows larger than the pump twin in the womb.

How is twin reversed arterial perfusion treated?

The goal of treatment for twin reversed arterial perfusion is to stop the blood flow to the acardiac/acephalic twin from the pump twin. This helps relieve some cardiac pressure for the pump twin, increasing his or her odds of survival and prevents other complications.

Your doctors will need to make sure the pump twin doesn’t have major chromosomal abnormalities. It is important to exclude a chromosomal abnormality before deciding upon a plan of treatment because the incidence of chromosomal abnormality in the pump twin may be as high as 9 percent. This may affect your course of treatment.

Some common treatments are:

• Bipolar cord coagulation. This fetal surgery is performed using small, hollow needles that are inserted into your abdomen. You receive an epidural anesthesia during the surgery. Your doctors insert a small device through the needle into the amniotic cavity (fluid filled space that surrounds the developing fetus) to stop blood flow to the acardiac/acephalic twin.
• Radiofrequency ablation (RFA). The RFA technique uses a needle that that is 1 mm diameter in size. It is placed through your abdomen and uterus. Then, it goes into the acardiac/acephalic twin’s umbilical cord to stop the blood flow. Because the needle is so small, it can make complications and an early delivery less likely. It is performed using a real-time ultrasound for guidance.
• Cord occlusion. During this non-surgical technique, a thread is tied around the umbilical cord of the acardiac/acephalic twin. This can be done with an ultrasound or through a combination of ultrasound-endoscopy.
• Laser photocoagulation. Laser energy seals off the communicating blood vessels on the placenta’s surface. A small incision is made on the skin so that a tiny camera can be inserted into the uterus. Then, the doctors will be able to see the blood vessels on the placenta. A laser light from the camera clots the blood vessels.

How will TRAP sequence treatment affect my baby?

After surgery, you may stay at the hospital for up to three days. Our doctors and nurses will provide around-the-clock care to make sure there aren’t any complications.

Most likely, your baby will be born early but will not have any problems or birth defects. If there are any complications, we will take your baby to our newborn intensive care unit (NICU) for specialized care.