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What is twin reversed arterial perfusion (TRAP)?

Twin reversed arterial perfusion (TRAP) occurs in identical twin pregnancies when one twin has an absent or non-functioning heart and receives all of its blood from the normally functioning and developing "pump twin."

  • The twins are joined by a large blood vessel between their umbilical cords.
  • The acardiac twin has no chance for survival.
  • The pump twin's heart works extra hard to pump to the acardiac (without a heart) twin, increasing the pump twin's risk of heart failure and death.
  • In addition, if both twins are in the same amniotic sac (usually), they may get entangled and twist the umbilical cord, resulting in sudden death.

Why and how often does TRAP occur?

We don’t know why it occurs, but it’s present in about 1 percent of identical twin pregnancies.

Twin Reversed Arterial Perfusion (TRAP) | Diagnosis & Treatments

How is TRAP diagnosed?

Your doctor will be able to make a diagnosis based on the mother’s prenatal ultrasound.

  • Often the pump twin's size will be larger than the acardiac twin.
  • Also the pump twin may develop polyhydramnios (excessive accumulation of amniotic fluid) and possibly heart failure, which can be seen on ultrasound.

If your doctor sees these signs, you may also get a fetal echocardiography, which looks directly at the heart of the pump twin.

How is TRAP treated?

Boston Children's treatment is aimed at saving the pump twin by separating the circulation between the twins.

This involves cutting the umbilical cord of the acardiac twin. The procedure is performed through a single puncture in the mother's abdomen.

This will increase the chance of survival in the pump twin by decreasing the potential for heart failure and death.

There is an increase in the potential for development of preterm labor after this procedure, and you will be monitored closely throughout the rest of your pregnancy.

How we care for TRAP

TRAP is a scary and complex condition. The Maternal Fetal Care Center (AFCC) is making a significant difference in the outcomes for families facing critical challenges to the health of their fetus or newborn.

Pushing beyond the pages of yesterday’s textbooks, we are rewriting what is possible in fetal medicine delivering hope — and healthy babies — through groundbreaking advancements and a commitment to the best in pediatric care.

Twin Reversed Arterial Perfusion (TRAP) | Programs & Services