Diagnostic dilemma in twin-reversed arterial perfusion sequence.

The twin-reversed arterial perfusion (TRAP) sequence is a rare complication of twin pregnancies. The anatomically normal twin is termed the pump twin; the recipient twin is malformed and is known as acardiac twin. It functions as a parasite to the pump twin and receives retrograde blood flow of poorly oxygenated blood from the pump twin via the abdominal aorta, resulting in a wide spectrum of malformations. The abnormal haemodynamics created in this situation can result in congestive heart failure, hydrops and consequent premature delivery of the pump twin such that the mortality rate may be as high as 50 %. We present a case of TRAP sequence in a twin pregnancy which was diagnosed at 35 weeks of gestation. It highlights the risk of monochorionicity-associated morbidity in multiple pregnancies.