To explore an appropriate time interval between oocyte retrieval and intracytoplasmic sperm injection (ICSI) for optimal embryological and clinical outcomes in ICSI cycles over 40 years of maternal age. A retrospective analysis of 1476 ICSI fresh cycles from women aged over 40 years, was performed at the Reproduction Medicine Research Center of the Sixth Affiliated Hospital of Sun Yat-sen University, between December 2013 and August 2020. The fertilization rate and clinical pregnancy rate were the main outcomes. Multivariate linear regression and logistic regression analysis of factors showed that fertilization rate (P = 0.024) and clinical pregnancy rate (P = 0.011) were significantly associated with oocyte pick up (OPU)-ICSI interval. A longer OPU-ICSI interval (no more than 6 h) was associated with a higher fertilization rate but significantly decreased the clinical pregnancy rate when the OPU-ICSI interval was over 4 h (P < 0.05). The optimal OPU-ICSI interval is between 3 and 4 h for excellent embryological and clinical outcomes in ICSI cycles over 40 years of maternal age.
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