Acardiac acephalus: Variant of trap sequence
The incidences of twin gestation and higher-order multi-fetal pregnancies are on increasing trend. There is increased use of ovulation induction drugs and assisted reproductive technology in this era owing to higher incidences of infertility and better diagnostics and treatment modalities. And with increased use of these methods, comes increased incidence of complications. Incidences of complications are more in monozygotic pregnancies than in dizygotic twin. Acardiac twin is a rare, severe congenital malformation seen in monozygotic twin gestation, which is incompatible with life. Acardiac twin, also known as TRAP (Twin Reversed Arterial Perfusion Sequence); results from abnormal placental vasculature. Early diagnosis of acardiac twin by ultrasonography and colordoppler is essential for timely management and preventing complications like preterm delivery, cardiac failure and intrauterine fetal death of ‘ pump’co-twin.

Regularsonographic surveillances should be initiated to assess the weight ratio of twins and signs of development of congestive cardiac failure and hydramnios in pump twin should be monitored. Weight can be estimated by comparing the ratio of the abdominal perimeter of the acardiac and pump twins, or by using the standard prolate ellipsoid formula. The prognosis of conservative management is excellent if the estimated weight of the acardiac twin is less than one-fourth of the pump twin. This is due to increased perfusion demands of the relatively large acardiac twin. In such cases, the donor twin (pump twin) has to maintain its own blood flow and also of the acardiac twin, and thus may lead to decompensation of the pump twin heart leading to failure. At this point, some form of minimally invasive intervention is warranted to interrupt the vascular communication between the twins.

Historically, uterotomy and removal of the acardiac twin is present in literature.Later, fetoscopic coagulation of placental anastomosis and endoscopic ligation of umbilical artery of acardiac twin have been described. Cord occlusion has been attempted by ultrasound-guided injection of thrombogenic materials into the umbilical circulation of the acardiac twin. Ligation of the umbilical cord, laser coagulation, bipolar diathermy, and monopolar diathermy are the other available options to interrupt the vascular anastomosis between the two twins. In comparison to the more invasive techniques for umbilical artery occlusion; Intra fetal ablation is more effective, safer and technically easier to perform. Greater than 90% survival of the pump twin is seen in TRAP Sequence treated with radiofrequency ablation. Recently, high intensity focused ultrasound (HIFU) has been used for occlusion of the blood flow in the acardiac twin.

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