Caesarean Scar Endometrial Defects Contribute to Post‐Caesarean Abnormal Uterine Bleeding and Chronic Endometritis: A Retrospective Case–Control Study

ABSTRACT Objective To explore the role of endometrial defects in the pathogenesis of abnormal uterine bleeding (AUB). Design Retrospective case–control study. Setting Two tertiary centres. Population or Sample We included 155 patients with caesarean scar defects (CSDs) who underwent hysteroscopy (69 AUB, 86 non‐AUB). Thirty patients with AUB were successfully matched with 30 patients without AUB after propensity score matching (PSM) based on CSD size and number of previous caesarean sections, which indicate myometrial defect severity. Methods Hysteroscopic features of CSD before and after PSM were compared between two groups. Pathological features of 13 patients in each group with biopsies of the CSD surface and uterine endometrium were compared, including endometrial thickness determined by haematoxylin–eosin staining, vascular density identified by CD31 staining and chronic endometritis assessed by plasma cells stained with CD138. Main Outcome Measures Incidence of hysteroscopic and pathological features of CSD. Results Before PSM, the AUB group exhibited larger diverticulum sizes and more severe myometrial CSD defects than the non‐AUB group. After PSM, five features of endometrial defects demonstrated statistically significant differences: in situ haemorrhage, bloody mucus, epithelial deficiency, exposed blood vessels and hyperplastic vessels. Pathological assessments also revealed significant differences in endometrial thickness of CSD, local vascularization and plasma cell count at CSD between the AUB and non‐AUB groups. Conclusions Endometrial defects at caesarean scars contribute more to AUB than myometrial defects.