Macroscopic and histological characteristics of retained placenta: A prospectively collected case-control study

• Retained placenta is a potentially fatal obstetric disorder for which the etiology is unknown.
• We assessed markers of maternal underperfusion in retained and non-retained placentas in healthy full-term pregnancies.
• Retained placentas had a smaller surface area, were more oblong in shape and showed overall more signs of underperfusion.
• In this regard retained placentas showed similarities to the macroscopic and histological features of preeclamptic placentas.
• Basal plate myometrial fibers, but not focal placenta accreta, were significantly more common among retained placentas.

IntroductionRetained placenta is a potentially fatal obstetric disorder due to postpartum hemorrhage, its pathophysiology is however unknown. We aimed to assess if retained placenta was associated with increased macroscopic and histological signs of placental maternal underperfusion, a pattern otherwise seen in preeclampsia and other disorders of defective placentation.MethodsThis was a case-control study of retained (n = 49) and non-retained (n = 47) placentas, collected from full-term singleton and otherwise healthy pregnancies, carried out at a tertiary level obstetric department. Macroscopic and histological analysis was performed. Signs of maternal placental underperfusion and signs of placental inflammation, fetal vascular thrombo-occlusive disease and increased placental attachment were recorded in a primary and secondary analysis respectively. Variables were compared groupwise using unconditional logistic regression or comparison of median or mean values.ResultsCompared to non-retained placentas retained placentas had a significantly smaller surface area (p = 0.05), were more oblong in shape (OR 5.24 95% CI:1.34–20.21) and showed overall more signs of maternal underperfusion (OR 2.52 95% CI: 1.07–5.87). There was no significant difference in signs of placental inflammation, fetal vascular thrombo-occlusive disease or placenta accreta but basal plate myometrial fibers were more common among retained placentas.ConclusionIn regard to shape, surface area and histological signs of maternal placental underperfusion, retained placentas showed a histological pattern similar to that seen in preeclamptic placentas.