The function of metformin in endometrial receptivity (ER) of patients with polycyclic ovary syndrome (PCOS): a systematic review and meta-analysis

BACKGROUND: This meta-analysis summarizes evidence from studies using metformin (Met) to improve endometrial receptivity (ER) in women with PCOS. METHODS: Following the PRISMA protocol, we conducted a comprehensive search of academic literature from various databases, including PubMed, EMbase and Cochrane libraries. Studies published in English before Jan 27, 2021, were recruited for primary screening. Data on endometrial thickness (EMT), endometrial artery resistance index (RI), clinical pregnancy rate (CPR) and miscarriage rate (MR) were extracted and analyzed. RESULTS: Sixty-two eligible studies that included 6571 patients were evaluated in this meta-analysis. Primary indicators are EMT and endometrial aetery RI; secondary indicators include the clinical pregnancy rate and miscarriage rate. Metformin significantly increased EMT (SMD = 2.04, 95% CI (0.96,3.12),P = 0.0002) and reduced endometrial artery RI compared to the non-Met group (SMD = − 2.83, 95% CI: (− 5.06, − 0.59), P = 0.01). As expected, metformin also improved CPR and reduced MR in PCOS patients as a result, clinical pregnancy rate (risk ratio [RR] = 1.26, 95% CI: 1.11–1.43, P = 0.0003), and miscarriage rate (RR = 0.73, 95% CI:0.58–0.91, P = 0.006). CONCLUSION: Metformin may improve endometrial receptivity (ER) in PCOS patients by increasing EMT and reducing endometrial artery RI. However, the level of most original studies was low, with small sample sizes. More large-scale, long-term RCTs with rigorous methodologies are needed.