Twin reversed arterial perfusion (TRAP) sequence: A case of an acardiac parabiotic twin

Twin Reversed Arterial Perfusion (TRAP) sequence is an uncommon and severe complication of monochorionic twin pregnancies, characterized by an acardiac twin lacking a functional heart and a pump twin that maintains circulation for both.

We report a case involving a 17-year-old primigravida diagnosed with a monochorionic diamniotic twin pregnancy at 8 weeks gestation. At 35 weeks, ultrasound revealed a teratogenous mass measuring 11 cm × 9.4 cm in the right fundal area, with bone-like particles, suggestive of an acardiac twin. An anomaly scan confirmed one live fetus and one edematous, non-viable fetus. At 36 weeks, an elective lower segment cesarean section was performed, delivering a healthy neonate followed by a dysmorphic, non-viable fetus weighing 626 g. The acardiac twin lacked a distinguishable head, body, or limbs, except for a rudimentary limb at the caudal end. Histological examination revealed skin-covered tissue with appendages, fibrous tissue, nerve bundles, blood vessels, and mature adipocytes, but no developed organs.

TRAP sequence results from abnormal vascular connections in the placenta, leading to reversed arterial perfusion of the acardiac twin. The pump twin is at risk of high-output cardiac failure, polyhydramnios, and preterm labour. Management strategies depend on the size ratio between twins and the pump twin's condition, ranging from expectant management to invasive interventions like radiofrequency ablation.

This case underscores the importance of early diagnosis and monitoring in monochorionic twin pregnancies to manage TRAP sequence effectively and improve outcomes for the pump twin.