Detection of twin reversed arterial perfusion sequence at the time of first-trimester screening: the added value of 3-dimensional volume and color Doppler sonography.

Twin reversed arterial perfusion (TRAP) sequence, also known as acardiac malformation, is a rare complication unique to monozygotic multiple gestations. It occurs in approximately 1 per 35,000 pregnancies and in 0.3% of all monozygotic twin gestations. The malformation is characterized by the lack of a well-defined cardiac structure in one twin (acardiac), which acts as a parasite that is hemodynamically dependent on the normal (pump) twin. The malformation in the acardiac twin is always incompatible with survival regardless of its extent, whereas the prognosis of the pump twin may vary considerably. Common complications that affect the prognosis of the pump twin include complications of prematurity secondary to preterm delivery and polyhydramnios as well as congestive heart failure due to the expended cardiac demand. Without prompt detection, follow-up, and treatment, mortality rates for pump twins have been noted to be as high as 50% to 70%. Early sonographic diagnosis, appropriate follow-up, and intervention via cord occlusion when indicated are the mainstays of prenatal care in cases of TRAP sequence and have been associated with substantial improvements in survival. We report a case that emphasizes the added value of 3-dimensional (3D) and color Doppler techniques for both diagnosis of TRAP sequence and detection of poor prognostic features in the first or early second trimester.