Spectrum of progression of TRAP sequence (acardiac anceps twin): a rare case report

TRAP (Twin reversed arterial perfusion) sequence is one such sequelae of monochorionic diamniotic multifetal pregnancy wherein one twin acts as a pump twin or perfusionist and second twin as an amorphous acardiac structure connected to this pump through an abnormal placental vascular anastomosis in reverse direction. This is an extremely rare complication occurring in 1 per 35,000 births. The acardiac twin which has either an absent, rudimentary, or non-functioning heart due to Compression of the cephalic pole of the embryo inhibiting curving and fusion of the primitive heart tube is the basic cause resulting in non-formation of the heart and other organs. However, whether this TRAP sequence is the cause or effect of acardia is still unknown. The mortality of pump twin is 50-75% and acardiac twin is 100%. The risk is directly dependent on the size of the acardiac twin: the higher the weight of the acardiac twin, the higher the risk of cardiac failure and death for the normal twin. Serial vigilant sonography and doppler evaluation is the "mainstay" in early detection of TRAP sequence. With advances in foetal medicine, many treatment options are available with minimally invasive techniques. We here presented one such rare case in which the diagnosis was reached quite early through sonography with doppler flow studies and it reemphasize the importance of ultrasonography as a simple but adequate tool not only in the diagnosis and follow-up but also in management of such a case.