Adenomyosis and chronic endometritis: cause, consequence or coincidence? A systematic review and meta-analysis

Chronic endometritis is persistent inflammation of the endometrium, often underdiagnosed due to its oligosymptomatic presentation. Both chronic endometritis and adenomyosis share inflammatory and structural alterations of the endometrial-myometrial interface that may impair reproductive outcomes. This systematic review and meta-analysis were conducted in accordance with the PRISMA guidelines, and registered in PROSPERO. MEDLINE, Embase, CENTRAL, Cochrane Database of Systematic Reviews, Scopus and trial registries were searched from 2000 to May 2025 to determine the prevalence of chronic endometritis in women with adenomyosis, and assess the strength of their association. Of 713 identified records, 10 studies (n = 2877 women) met the inclusion criteria. The pooled prevalence of chronic endometritis in women with adenomyosis was 32% (95% CI 16-53; I² = 94%). In subgroup analyses, prevalence varied by the diagnostic method used for adenomyosis: hysterectomy (21%), magnetic resonance imaging (64%), and hysteroscopy (8%). Meta-analysis demonstrated a significantly higher prevalence of chronic endometritis in women with adenomyosis compared with controls (OR = 3.81, 95% CI 2.23-6.50; I² = 11%). This systematic review and meta-analysis suggest that adenomyosis and chronic endometritis frequently coexist, with women with adenomyosis showing a significantly higher risk of chronic endometritis. Standardized diagnostic criteria, adenomyosis subtype classification, and high-quality randomized controlled trials are needed to clarify the underlying mechanisms, and are necessary to demonstrate an association between adenomyosis and chronic endometritis.