Twin Reversed Arterial Perfusion Sequence

Abstract Twin reversed arterial perfusion (TRAP) sequence is a rare complication specific to monochorionic twin pregnancies in which a dysmorphic acardiac fetus receives circulatory support from a pump twin via aberrant placental arterioarterial anatomoses. The hemodynamic burden of supporting an acardiac mass places the pump twin at risk for polyhydramnios, heart failure, hydrops, and death. A TRAP diagnosis is secured by ultrasound, with necessary findings including a normal-appearing pump fetus and a grossly abnormal acardiac twin in the setting of a monochorionic pregnancy, with color Doppler study demonstrating reversal of arterial flow to the acardiac fetus. Due to an increased rate of aneuploidy, invasive genetic testing is recommended for pregnancies complicated by TRAP sequence. Therapy with invasive cord occlusion to sever the intertwin vascular circuit should be considered with a relatively large acardiac twin or when pump twin compromise is suspected at a previable gestational age, with radiofrequency ablation (RFA) a commonly used contemporary cord occlusion strategy for this presentation.