What is an acardiac twin or twin reversed arterial perfusion (TRAP) syndrome?
An usual form of TTTS occurs in about one in 15,000 pregnancies. In these monochorionic twins, one twin develops normally while the other twin fails to develop a heart as well as other body structures. The abnormal twin is called an acardiac twin. In these pregnancies, the umbilical cord from the acardiac twin branches directly from the umbilical cord of the normal twin. Blood flow to the acardiac twin comes from the normal twin, which is also known as a pump twin. This blood flow is reversed from the normal direction leading to the name for this condition: twin reversed arterial perfusion syndrome or TRAP. In some cases the blood flow from the pump twin to the acardiac twin stops on its own and the acardiac twin stops growing. In other cases, the flow continues and the acardiac twin continues to increase in size. This eventually leads to heart failure and polyhydramnios in the pump twin. Without treatment, more than 50 percent of cases of TRAP will result in the death of the pump twin
