Third trimester bleeding is a major cause of maternal death, and perinatal morbidity and mortality. Bleeding from ruptured vasa previa is the only cause of pure fetal hemorrhage. Adherent, sometimes laminated blood clot, occasionally dissecting into the adjacent parenchyma, may be seen with a recent abruption. The clot of an older abruption is firm, dry and stringy, and eventually brown. Grossly, infarcts are firm due to the crowded villi.
Acute infarcts are grossly firm and microscopically show villous congestion.
Older infarcts are grossly yellow-white and microscopically demonstrate progressive loss of nuclear staining, initially of the trophoblast and finally of the entire villus with fibrin deposition in the intervillous space. Marginal infarcts seen in otherwise normal term placentas are common and have no significance for the mother or fetus. However, any infarct in a premature placenta is abnormal. Large infarcts, even at term, greater than 3 cm and especially if centrally located, are definitely abnormal. Such infarcts are associated with serious perinatal morbidity and mortality.