Twin Reversed Arterial Perfusion Sequence (TRAP)

Sometimes referred to simply as “acardiac twin,” twin reversed arterial perfusion (TRAP) sequence is a rare disorder that affects unborn monochorionic twins, or twins who share a placenta in the mother’s womb. This condition is characterized by one twin (the “pump twin”) who works to supply blood for both babies, and one twin (the acardiac twin) who is poorly formed, usually missing a functioning heart, head, limbs or torso.

While the pump twin in a TRAP sequence pregnancy is normally developed, pumping blood for the acardiac twin places immense strain on the heart, increasing the risk of cardiac failure and other complications. Prompt intervention to cut off the blood supply to the acardiac twin is key to delivering a healthy baby. The acardiac twin has no chance of survival, as it does not have a beating heart and is missing other essential organs.

TRAP Sequence Causes

Twin reversed arterial perfusion sequence is very uncommon, occurring in only about 1% of monochorionic twin pregnancies. The exact cause of TRAP sequence is not clear, although some researchers believe prolonged fluctuation in blood flow and blood pressure may impact heart development in the acardiac twin. There are currently no known risk factors for TRAP sequence.

TRAP Sequence Symptoms

In twin reversed arterial profusion sequence, the pump twin must labor to supply blood to the acardiac twin. The pump twin’s risk of experiencing cardiac failure increases as the acardiac twin grows larger. TRAP sequence can also increase blood flow to the pump twin’s kidneys, leading to an excess of fetal urine that may cause polyhydramnios and preterm labor.

TRAP Sequence Diagnosis

Signs of twin reversed arterial profusion sequence are often identified on a routine pregnancy ultrasound, which may show a normally growing fetus and an abnormal tissue mass with no cardiac activity. Additional ultrasound testing to observe blood flow patterns may be performed to confirm a diagnosis.

TRAP Sequence Treatments

Tampa General Hospital provides advanced prenatal care to women with twin reversed arterial profusion sequence and other complex pregnancy conditions. Our diverse treatment teams include maternal-fetal medicine specialists, neonatologists, fetal surgeons and other experts who collaborate to achieve world-class outcomes for high-risk obstetrics patients. Treatment options for TRAP sequence focus on sealing off the pump twin’s blood supply to the acardiac twin, which can be achieved through radiofrequency ablation (RFA) or bipolar coagulation, depending on the healthy baby’s gestational age.