Pathological Findings in Feto-maternal Hemorrhage.

Feto-maternal hemorrhage (FMH) is the cause of late fetal death in 1.6%-11% of cases. In spite of this high frequency, its pathological features have received little attention. The definitive diagnosis of lethal FMH requires confirmation of sufficient fetal blood volume loss. This is determined by tests such as the Kleihauer-Betke test, which may not have been obtained or not have been available before the autopsy. The pathologist may offer a tentative diagnosis of FMH from the autopsy findings. The objective of this study was to better characterize the placental and fetal autopsy findings in lethal FMH. This was a retrospective study of 17 cases of FMH proven by a positive Kleihauer-Betke test. The cases were selected from the autopsy files of the Department of Pathology, Centre Hospitalier Universitaire de Bordeaux. The pathological reports as well as the placental and fetal photographs and the microscopic slides of each case were systematically reviewed. The fetal autopsy findings in FMH are characterized by a eutrophic pale macerated fetus, low liver weight, absent intrathoracic petechiae, increased extramedullary hematopoiesis in the liver and kidney, and increased circulating nucleated red blood cells. The placenta shows an increased frequency of intervillous thrombi. Although nonpathognomonic, some of the pathological features are strongly suggestive of FMH. When the latter is present, a Kleihauer-Betke test should be performed, even some days after the delivery.