Determinants of clinical pregnancy outcomes in women with diminished ovarian reserve undergoing repeated assisted reproductive technology cycles: a retrospective cohort analysis of 3,895 oocyte retrieval cycles.

Objective: This study aimed to evaluate factors associated with the clinical pregnancy rate in women with diminished ovarian reserve (DOR) undergoing repeated assisted reproductive technology (ART) cycles. Methods: A retrospective analysis was conducted on 3,895 oocyte retrieval (also referred to as oocyte pickup, [OPU]) cycles and 1,545 frozen embryo transfer cycles from 899 women with DOR. Multivariate logistic regression was used to identify independent factors associated with clinical pregnancy. Restricted cubic spline models were applied to assess potential non-linear relationships between key variables and pregnancy outcomes. Stratified analyses were performed according to age, first-cycle oocyte yield, number of OPU cycles, and cumulative oocyte yield. Results: The median age of the study participants was 35 years. Multivariate logistic regression analysis demonstrated that increasing age (OR = 0.89) and the total number of OPU cycles (OR = 0.92) were independently associated with lower clinical pregnancy rates. In contrast, first-cycle oocyte yield (OR = 1.11) and cumulative oocyte yield (OR = 1.04) were independently associated with higher clinical pregnancy rates. Restricted cubic spline analysis identified non-linear associations between key variables and clinical pregnancy outcomes. In the overall cohort, the clinical pregnancy rate declined with increasing age beyond approximately 32years, while no further increase was observed when cumulative oocyte yield exceeded approximately 15. Stratified analyses demonstrated that among women aged<33 and 33 to 37 years, the clinical pregnancy rate increased with cumulative oocyte yield up to approximately 9 oocytes, after which a plateau was observed. In women who obtain 0-1 oocytes in the first cycle, the probability of successful pregnancy gradually decreases with age after about 34 years old. And similar to women who obtained ≥4 oocytes in the first cycle, pregnancy success rates also decrease with the increase of OPU cycles after about 4 OPU cycles. In women who obtained 2-3 oocytes in the first cycle, pregnancy success rates began to decline after around the age of 32. In women undergoing 1-2 OPU cycles, clinical pregnancy rates increased with cumulative oocyte yield up to approximately 7 oocytes and declined thereafter. Among women with 3-4 OPU cycles, clinical pregnancy rates increased with cumulative oocyte yield up to approximately 14 oocytes and decreased beyond this inflection point. When cumulative oocyte yield ranged from 6 to 10, clinical pregnancy rates increased up to approximately 32 years of age and declined thereafter. For cumulative oocyte yield ≥ 11, clinical pregnancy rates remained relatively stable before approximately 32 years of age and decreased subsequently. Conclusion: Advancing age is an independent risk factor associated with reduced clinical pregnancy rates in women with DOR, with approximately 32 years representing a critical inflection point for reproductive potential. A inflection point effect was observed between cumulative oocyte yield and clinical pregnancy rate. Moderate increases in oocyte yield are associated with improved clinical outcomes; however, the benefit diminishes beyond a certain inflection point.