What is vanishing twin syndrome?

Demise of one fetus: Vanishing twin syndrome is the demise of one twin sometime during the pregnancy. One study suggested it occurred about 20-30% of twin pregnancies. Most commonly it occurs early in the pregnancy and generally the remaining fetus has a good outcome. Its' occurrence later in pregnancy can be associated with adverse maternal and fetal outcomes.

Dissapearance of one: Vanishing twin syndrome is the identification of a multifetal gestation with subsequent disappearance of one or more fetuses. In vanishing twin syndrome, there may be complete reabsorption of a fetus, formation of a fetus papyraceus (ie, a "mummified" or compressed fetus), or development of a subtle abnormality on the placenta such as a cyst, subchorionic fibrin, or amorphous material.