Twin Reversed Arterial Perfusion Sequence With Acardius Acormus: The Role of 3D Imaging and Pelvimetry in Obstetric Planning

Twin Reversed Arterial Perfusion (TRAP) sequence is a rare complication of monochorionic pregnancies in which an acardiac twin is perfused retrograde via placental arterio-arterial anastomoses from a structurally normal "pump" twin. We present the case of a G2P1 (two pregnancies and one delivery at a viable gestational age) 27-year-old woman at 33 weeks of gestation referred for an ultrasound due to a suspected placental tumor. Imaging revealed a normally developing fetus and an additional malformed fetal-like structure with reversed blood flow, leading to a diagnosis of acardius acormus, a rare morphological subtype of the TRAP sequence. This case highlights the utility of advanced imaging modalities, including 3D ultrasound, Doppler studies, and MRI, in the diagnosis, monitoring, and delivery planning of complex twin pregnancies involving TRAP.