What can we learn from the histopathology of retained placenta? A 15-year experience at a regional referral center

BACKGROUND: The aim of this study was to retrospectively review the histopathology reports of retained placentas in search of potential histologic pathogenetic markers and clinical predictive factors. METHODS: Clinical and histopathological features of 86 cases of retained placenta over a 15-years period in a large regional referral center were retrospectively examined and compared. RESULTS: Retained placenta is a complication occurring in less than 0.4% of the total assisted deliveries and is mainly seen in primiparae/primigravidae in their mid-thirties. No relevant alterations of maternal health were observed during pregnancy. Several of our patients had positive family history for hypertension and metabolic diseases (37.21% and 33.72%, respectively). No cases of severe fetal disease or twin pregnancies were observed. Superficial placental accretion (8.3%) and chorioamnionitis (33.73%), usually associated with retained placenta, resulted uncommon and too mild to justify the onset of the condition. On the contrary, we observed an increased frequency of hypoxic/ischemic lesions (46.51%) or lesions related to maternal hypertension (15.12%). CONCLUSIONS: Retained placenta would appear to be caused by pathological adhesion of the chorionic disc to the decidua that seems to be unrelated to maternal or fetal disease but that is more likely linked to an adaptive hypoxic and/or ischemic state, which often coexists with maternal hypertension.