Objective:To evaluate the effect of prolonged cryopreservation duration of high-quality embryos on clinical outcomes.Methods:A retrospective cohort study was conducted, analyzing 8 988 frozen-thawed embryo transfer cycles performed from January 2016 to December 2023 at the Center for Reproductive Medicine, Chongqing Maternal and Child Healthcare Hospital where patients underwent endometrial preparation with artificial cycles and subsequent transfer of high-quality embryos. Embryos were divided into four groups according to the length of time they had been cryopreserved: ≤3-month group ( n=3 030), 4-6-month group ( n=3 193), 7-12-month group ( n=1 465), and >12-month group ( n=1 300). High-quality cleavage-stage embryos and blastocysts were selected according to the Istanbul Consensus and Gardner grading system. High-quality cleavage-stage embryos were defined as those graded ≤2, while high-quality blastocysts were defined as those graded ≥4BB. Generalized estimating equations were employed for multivariate analysis. Primary outcome indicator was clinical pregnancy rate, with secondary outcome indicators comprising live birth rate, miscarriage rate and preterm birth rate. Results:Significant intergroup differences were observed in baseline characteristics, including age, body mass index, anti-Müllerian hormone levels, fertilization method, endometrial thickness on transfer day, infertility etiology, infertility type, number of embryos transferred, embryo culture duration, number of eggs obtained, and preimplantation genetic testing (all P<0.05). Clinical pregnancy rates for the ≤3-month, 4-6-month, 7-12-month, and >12-month groups were 69.04% (2 092/3 030), 70.15% (2 240/3 193), 61.16% (896/1 465), and 57.69% (750/1 300), respectively, and live birth rates were 58.58% (1 775/3 030), 60.04% (1 917/3 193), 51.40% (753/1 465), and 47.00% (611/1 300), with significantly differences (all P<0.001). After adjusting for confounders via multivariate analysis, the 4-6-month group showed no statistically significant difference in clinical pregnancy rate or live birth rate compared with the ≤3-month group (clinical pregnancy: OR=0.982, 95% CI: 0.874-1.103, P=0.754; live birth: OR=0.989, 95% CI: 0.887-1.102, P=0.835). However, both the 7-12-month group (clinical pregnancy: OR=0.772, 95% CI: 0.671-0.888, P<0.001; live birth: OR=0.805, 95% CI: 0.704-0.921, P=0.002) and >12-month group (clinical pregnancy: OR=0.765, 95% CI: 0.662-0.885, P<0.001; live birth: OR=0.772, 95% CI: 0.671-0.888, P<0.001) exhibited significant decreases in clinical pregnancy rate and live birth rate. No significant differences were observed in miscarriage rate and preterm birth rate among the four groups (all P>0.05). Stratified by age, the results were consistent with the total population. Conclusion:The duration of high-quality embryo vitrification freezing exceeding 6 months is negatively correlated with clinical pregnancy rate and live birth rate, and cryostorage time should be considered as a relevant factor in embryo selection.