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RESEARCH QUESTION What is the relationship between uterine volume before frozen-thawed embryo transfer (FET) and reproductive outcomes among adenomyosis patients? DESIGN Clinical characteristics and outcomes of adenomyosis patients undergoing IVF and FET in a tertiary academic hospital were retrospectively analysed. Only first blastocyst transfer cycles were included. The main outcome measures included clinical pregnancy rate (CPR), miscarriage rate and live birth rate (LBR). RESULTS A total of 158 adenomyosis patients were enrolled. Receiver operating characteristic (ROC) curve analysis indicated that uterine volume before FET was negatively related to LBR, with area under the curve of 0.622 (95% confidence interval [CI] = 0.531-0.712, P = 0.012). The cut-off value for the curve was 98.81 cm3. Grouped by the cut-off of uterine volume, 83 women were included in group A (≤98.81 cm3) and 75 in group B (>98.81 cm3). No significant difference was found in CPR between two groups. Compared with group A, the incidence of miscarriage in group B was significantly increased (51.28% versus 16.28%, P = 0.001). LBR in group B was markedly lower than in group A (25.33% versus 43.37%, P = 0.020). Logistic regression analysis revealed that, after adjusting for potential confounders, uterine volume before FET was not associated with CPR (odds ratio [OR] 1.149, 95% CI 0.577-2.286, P = 0.693) but was positively related to miscarriage rate (OR 8.509, 95% CI 2.290-2.575, P = 0.001). CONCLUSIONS Adenomyosis patients with larger uterine volume (>98.81 cm3) before FET might have a lower LBR due to higher incidence of miscarriage. Reduction of uterine volume before embarking on FET procedures should be recommended.