Premature birth lacks a widely accepted classification that unites features of the clinical presentation with placental pathology. To further explore associations between the clinical categories of preterm birth and placental histology, 109 infants with gestational age <34 weeks and birth weight <2000 g were selected and, based on electronic records, were classified into preterm birth categories of preterm labor, prelabor premature rupture of membranes, preeclampsia, indicated preterm birth for maternal factors (other than preeclampsia), indicated preterm birth for fetal factors, and the clinical diagnosis of abruption. Corresponding placentas were analyzed for gross and microscopic variables, with findings grouped into categories of amniotic fluid infection, lymphocytic inflammation, maternal vascular malperfusion, and fetal vascular malperfusion. Placental features of maternal vascular malperfusion were pervasive in all preterm birth categories and were commonly associated with amniotic fluid infection and lymphocytic inflammation. Features of maternal vascular malperfusion were significantly associated with preterm birth due to preeclampsia, and amniotic fluid infection was highly associated with prelabor preterm rupture of membranes. Findings of lymphocytic inflammation were significantly increased in cases of abruption. Laminar decidual necrosis was present in all cases of abruption. Placentas from multiple gestations had significantly less histologic findings compared to singletons. Given that 75% of placentas demonstrated at least 1 feature of maternal vascular malperfusion despite different clinical presentations, seemingly different pathologies such as ascending amniotic fluid infection or lymphocytic inflammation may be mechanistically related to processes established early in pregnancy. The concept of "uterine ischemia" may be too simplistic to account for all of the changes attributed to maternal vascular malperfusion in the preterm placenta.
Keywords: amniotic fluid infection; chronic inflammation; placenta histology; preeclampsia; preterm birth.