[Acardiac fetus].

Acardiac fetus is a rare lethal fetopathy usually encountered in monozygous pregnancies. Ultrasound prenatal diagnosis has enabled an increasing number of observations and raised the need for an adequate therapeutic approach since the spontaneous prognosis for the healthy twin is unfavorable in half of the cases. An acardiac fetus was identified at 12 weeks gestation in a 36-year-old woman. Growth of the healthy fetus was carefully monitored and progressed normally to delivery by cesarean section of a 2.900 kg boy at 36 weeks. At delivery, the acardiac fetus was found to be totally free of any attachment, floating in the remaining fluids. Pathology examination showed a 16 g macerated fetus with a cephalic extremity, a ventral pedicle and a syrenomelic caudal extremity. The caryotype was not significative. Acardiac fetus occurs in less than 1% of multiple pregnancies and can develop in single pregnancies. Twin reversed arterial perfusion has been recognized as necessary for development of the perfused fetus. Genetic and immunologic theories have been proposed to explain the pathogenesis which remains unknown. Clinical management depends on the spontaneous development of the acardiac fetus and the deleterious consequences for the healthy twin resulting from heart failure, anasarca or prematurity. Medical management with digoxin, or selective extraction by hysterotomy may improve prognosis but results have been variable. Echoguided umbilical cord ligation has also been proposed to improve maternal mortality. Therapeutic abstention is no longer indicated at prenatal diagnosis of an acardiac fetus and a healthy twin despite the risk of invasive treatment.