TWIN REVERSED ARTERIAL PERFUSION SEQUENCE (TRAP SEQUENCE). THE ACARDIAC /ACEPHALIC TWIN

Twin-Reversed Arterial Perfusion (TRAP sequence) is a rare complication of monochorionic twins (MC, twins sharing one placenta). TRAP sequence is known as acardius or chorioangiopagus parasiticus. It occurs in 1% of monochorionic twin pregnancies and in 1 in 35,000 pregnancies. The risk of recurrence was estimated 1:10,000. TRAP sequence is characterized by a structurally normal pump twin perfusing an anomalous twin. In TRAP syndrome, there is mortality and deformities in both twins. The acardiac/acephalic twin is a parasitic twin that fails to develop a head, arms and a heart. The parasitic twin is with or without legs, receives its blood supply from the host twin (Pump twin). In TRAP sequence, one twin is usually developmentally normal (pump twin) and the other twin has a serious condition, either missing a heart (acardiac) or a head (acephalic) or both, that prevents it from surviving on its own. The acardiac/acephalic twin receives all of its blood from the normal or “pump” twin. The abnormal fetus does not have a heart; all of its blood must come from the normal twin. And it is kept alive by the blood which is pumped from the normal twin through the placenta. The term “reversed perfusion” is used to describe this scenario because blood enters the acardiac/acephalic twin through reversed flow through its umbilical artery and exits through the umbilical vein, which is opposite to the normal blood supply of the fetus.The acardiac twin loses direct vascular connection with the placental villi and receives its entire blood supply from the pump twin [1,2,3,4]. Proper timing of the delivery is of prime importance for the survival of the normal fetus. The emphasis is placed on close sonographic monitoring from early antenatal diagnosis. The mortality of the acardiac twin is 100%, and the perinatal mortality of the pump twin is reported to be around 50%. The mortality rate of the pump twin appears to correlate with the size of the acardiac twin and primarily due to congestive heart failure. We present such a case of TRAP sequence because of its rarity. TRAP sequence, was diagnosed by ultrasound at the obstetrics and gynecology department at KAMS & RC (Kamineni) and it was closely followed up until delivery. Clinical presentation, ultrasound findings, outcome and management were reviewed in present article.