Expectant Management of an Acardiac Twin Pregnancy

Definition: A complication of monozygotic twin pregnancies in which one fetus develops normally (pump twin) and the second twin (recipient twin) demonstrates cardiac mal development ranging from complete absence of heart tissue to some formation of rudimentary myocardia. Etiology: Probable reversal of circulation in the anomalous twin resulting from anastomosis of circulation between the twins Pathogenesis: Malformation of the heart and heart dependent endodermal organs in the anomalous twin. Associated anomalies: In the perfused twin: total or partial absence of cranial vault, holoprosencephaly, anencephaly, absent facial structures, anophthalmia, microphthalmia, cleft lip, cleft palate, absent or rudimentary limbs, diaphragmatic defects, absent lungs and heart, esophageal atresia, ventral wall defects, ascites, absent liver and gallbladder, edema of the skin and single umbilical artery. In the pump twin: evidence of congestive heart failure (ascites, pleural effusions, polyhydramnios, skin edema). Differential diagnosis: Cystic hygromas, singleton pregnancies with intraamniotic tumors, pseudoacardiac twin. Prognosis: Uniformly lethal for the recipient twin; perinatal mortality rates reported up to 50 percent in pump twin. Recurrence risk: Not increased. Management: Serial ultrasound for evaluation of growth and signs of congestive heart failure in the normal twin.