Vascular lesions, most often mediated by thrombi, are second only to infections as a cause of fetal injury in the later weeks of pregnancy. In our experience many pathologists who examine placentas fail to conduct a proper search for vascular lesions and some even fail to recognize those exposed by their examination. This review is intended to define the typical clinical background or circumstances that suggest the presence of significant vascular problems, to define techniques calculated to display them well, and to identify criteria for diagnosis. Further research is needed to evaluate the prevalence of maternal and fetal hypercoagulable states and thrombi as a cause of fetal injury.