Twin reversed arterial perfusion

Twin Reversed Arterial Perfusion (TRAP) sequence is a rare complication of monochorionic twin pregnancies, where one twin (the "pump twin") provides circulatory support to the other twin (the "acardiac twin"), which lacks a functional heart. This condition is also known as acardiac twinning and is a form of Twin-to-Twin Transfusion Syndrome (TTTS), although it presents uniquely due to the acardiac twin's reliance on the pump twin for blood circulation.

Etiology

The exact cause of TRAP sequence is not fully understood, but it is believed to result from abnormal placental vascular connections that allow arterial blood from the pump twin to flow into the acardiac twin. This reversed flow leads to the development of an acardiac fetus, which typically lacks a fully formed heart and other upper body structures, depending on the severity of the condition.

Pathophysiology

In TRAP sequence, the pump twin's heart works harder to support both fetuses, leading to potential heart failure and other complications such as Polyhydramnios and Hydrops Fetalis. The acardiac twin, on the other hand, may develop a range of malformations, often being partially or completely missing the upper body, including the heart, hence the term "acardiac."

Diagnosis

Diagnosis of TRAP sequence is usually made through Ultrasound imaging during pregnancy. Key indicators include the presence of a monochorionic twin pregnancy, identification of one twin with severe malformations and lack of a functional heart, and the observation of reversed arterial blood flow from the healthy twin to the malformed twin.

Management

Management of TRAP sequence aims to reduce the risks to the pump twin while considering the viability of the pregnancy. Options include careful monitoring, Amnioreduction to manage polyhydramnios, and in some cases, fetal intervention. Fetal intervention may involve procedures such as radiofrequency ablation (RFA) or laser coagulation to disrupt the blood flow to the acardiac twin, thereby reducing the burden on the pump twin's heart.

Prognosis

The prognosis for TRAP sequence varies depending on the severity of the condition and the timing and effectiveness of treatment. The pump twin has a higher risk of morbidity and mortality, primarily due to heart failure and the complications of prematurity. With appropriate management, however, the survival rate of the pump twin can be significantly improved.

Epidemiology

TRAP sequence is a rare condition, occurring in approximately 1% of monochorionic twin pregnancies and 1 in 35,000 pregnancies overall. It is more common in pregnancies resulting from assisted reproductive technologies.

See Also

• Twin-to-Twin Transfusion Syndrome
• Monochorionic Twins
• Polyhydramnios
• Hydrops Fetalis