To evaluate the impact of untreated chronic endometritis (CE) on in vitro fertilization (IVF) outcomes, with a specific focus on the differential effects of embryo transfer protocols and CE severity (stratified by CD138-positive plasma cell count). We systematically searched PubMed, Web of Science, Scopus, the Cochrane Library, CNKI, Sinomed, VIP, and WanFang databases from their respective inception dates to 30 September 2025 for studies comparing IVF outcomes between women with untreated CE and those without CE. The quality of included studies was assessed using the Newcastle-Ottawa Scale. Disease severity was stratified as mild (1–4 CD138 + plasma cells per high-power field HPF) or severe (≥ 5 cells/HPF). The primary outcome was clinical pregnancy rate, while secondary outcomes were the live birth rate, early miscarriage rate, and embryo implantation rate. A total number of 3190 patients from ten studies were included. The overall analysis revealed that untreated CE was associated with a significantly reduced clinical pregnancy rate (nine studies, OR = 0.52, 95% CI: 0.32–0.84, p value = 0.008) compared to those without CE. Subgroup analysis within the frozen embryo transfer (FET) population revealed that mild CE (1–4 CD138 + plasma cells/HPF) showed no significant association with clinical pregnancy rate (four studies, OR = 0.94, p value = 0.78), severe CE (≥ 5 CD138 + plasma cells/HPF) was associated with reduced clinical pregnancy rate (three studies, OR = 0.26, p value = 0.02). Furthermore, the association of severe CE appeared to be stage-specific, being significantly associated with lower clinical pregnancy but not with embryo implantation rates, live birth rates, or early miscarriage rates in the FET population. This meta-analysis indicates that the severity of untreated chronic endometritis (CE) is associated with IVF outcomes in FET cycles. Women with severe CE (≥ 5 CD138 + cells/HPF) had lower clinical pregnancy rates, while those with mild CE (1–4 CD138 + cells/HPF) showed no significant association. This dose-response relationship underscores the importance of CD138 + based severity stratification and contributes to explaining a key source of heterogeneity in the existing literature. These findings warrant validation in prospective studies to define management thresholds. CRD420251266243.
Kong et al. (2026) studied this question.