Placental pathology: a systematic approach with clinical correlations

Despite advances over the past 25 years in the monitoring of in utero fetal status, the gravid uterus remains a "black box" integrating underlying genetic risk factors, preexisting maternal disease, and injurious extrinsic events in a poorly understood way to produce an evolving state linked to pregnancy outcome. It is currently believed that many short- and long-term adverse pregnancy outcomes and even some long-term chronic diseases extending into adult life are at least in part determined by processes occurring during intrauterine life. The placenta has been described as a "diary of intrauterine life" and has the potential to illuminate many aspects of these processes. Unfortunately a systematic and objective catalog of placental abnormalities has never been agreed upon. This report outlines a simple conceptual framework separating placental patterns of injury and maladaptation into three categories of lesions affecting the maternal and fetal vasculature (maldevelopment, obstruction, and disruption) and two categories of inflammatory lesions (infectious and idiopathic). Data are presented supporting the importance of these processes for an understanding of preterm delivery, intrauterine growth restriction, hypoxic-ischemic injury, and recurrent pregnancy loss.