Impact of a Thickened Endometrium on Pregnancy Outcomes in Frozen-Thawed Embryo Transfer: A Retrospective Cohort Study

Objective: To assess the impact of an excessively thick endometriumon pregnancy outcomes in frozen-thawed embryo transfer (FET) cycles. Design: Retrospective cohort study. Setting: A university-affiliated reproductive medicine center. Population: A total of 6,222 FET cycles (involving 5,434 women) with an endometrial thickness (EMT) ≥11 mm performed between January 2018 and December 2023. Methods: The association between EMT and outcomes was visualized using dual-axis combination plots and conditional density plots (CDPs). To account for the correlation between multiple cycles within the same patient and potential confounders, generalized estimating equations (GEE) were employed. Main Outcome Measures: Clinical pregnancy rate (CPR) and live birth rate (LBR). Results: Baseline characteristics were comparable across five EMT groups (11 to