Intrauterine death of a twin: mechanisms, implications for surviving twin, and placental pathology.

In multiple gestations, intrauterine death of one fetus occurs frequently. Sonographic studies indicate that many twin pregnancies are converted in early pregnancy to singletons. The "vanished" twin is sometimes recognized as a fetus papyraceous (compressus) incorporated into the placenta of the survivor. Death of one twin later in pregnancy may have serious implications for the survivor, especially in cases of monochorionic twins. One postulated mechanism has been that thromboplastic proteins from the dead twin are transfused into the survivor's circulation, resulting in disseminated intravascular coagulation. More recently it has been proposed that massive blood loss may occur from the survivor into the more relaxed circulation of a dead monochorionic twin through vascular anastomoses. These mechanisms may explain the higher frequency of cerebral palsy in monochorionic twins. These concepts emphasize the importance of careful examination and thoughtful interpretation of twin placentas.