Implications of chronic inflammation, endometrial dysfunction, and vascular remodeling in uterine niches (cesarean scar defects) associated with abnormal uterine bleeding and infertility: a systematic review

AimTo review the pathological findings of uterine niches in women presenting with infertility and abnormal uterine bleeding. MethodsThe Medline, Embase, and Cochrane Central databases were searched until 1 May 2025. We included cohorts, case-controls, and case series. The risk of bias was evaluated with ROBINS-I, and the certainty of evidence was presented according to GRADE. ResultsWe included fourteen studies (637 women). Chronic inflammation was observed in 54% (95% CI 25 to 81%; 5 studies, 280 women; I2 = 94.3%); fibrosis in 83% (95% CI 51 to 96%; 6 studies, 266 women; I2 = 92.1%); endometrial defects in 90% (95% CI 75 to 96%; 4 studies, 177 women; I2 = 64.6%); ectopic endometrium in 26% (95% CI 18 to 36%; 9 studies, 411 women; I2 = 74.2%); and vascular remodeling in 81% (95% CI 75 to 86%; 6 studies, 205 women; I2 = 0.0%). There was an increased risk of endometrial defects in women with niches compared to those with prior cesarean deliveries (RR 2.13, 95% CI 1.27 to 3.55; 2 studies, 124 women; I2 = 0.0%), similarly for ectopic endometrium (RR 2.86, 95% CI 1.03 to 7.96; 2 studies, 97 women; I2 = 0.0%). Additionally, niches exhibited a pro-inflammatory phenotype, characterized by elevated expression of CD138 and TNF-. ConclusionsThe observed pathological features suggest an underlying process driven by the interplay of chronic inflammation, altered immune cell recruitment, fibrosis, and vascular remodeling within the regenerating endometrium. Registration numberCRD420251049667.