Abstract: Objective：To compare the effects of two different ICSI insemination times on the reproductive outcomes of fresh embryo transfer (FET) in gonadotropin-releasing hormone (GnRH) antagonist cycles. Methods：531 cycles of FET after the GnRH antagonist protocol were divided into two groups according to the interval time between OPU and ICSI, the group one (n=101) that the OPU-ICSI interval was ranged from 38～40 h and the group two (n=430) was 41～43 h. The differences of oocyte maturation rate, embryo quality and pregnancy outcomes between the two groups were analyzed retrospectively. Results：The oocyte maturation rate was significantly lower in the group one when compared with the group two (P＜0.05), and the miscarriage rate in group one was significantly higher (P＜0.05). There was no significant differences in the fertility rate, cleavage rate, available embryo rate, high-quality embryo rate, implant rate and pregnancy rate between the two groups (P＞0.05). Conclusions：Our results indicate that there are relatively consistent embryo quality and clinical pregnancy rate in the timing of ICSI ranged from 38～43 h. As for the finding that the miscarriage rate could be higher if the ICSI time was earlier than 40 h in the FET cycle of GnRH antagonist protocol, we think that more studies with large samples and the detailed grouping may be necessary.ds: 531 patients were divided into two groups according to times between hCG and ICSI from January 2016 to May 2018. The hCG-ICSI interval ranged from 38h to 40h was group one (including 101 cases) and 41h-43h was group two (including 430 cases). The differences of oocyte maturation rate, quality of embryo and reproductive outcomes between the two groups were analyzed retrospectively. Result: The oocyte maturation rate of Group one was significantly lower than Group two (P<0.05), furthermore miscarriage rates when ICSI was performed 38-40 hours in Group one was significantly higher than Group two(P<0.05). There was no significant difference in fertility rates, cleavage rates, available embryo rates, high-quality embryo rates, implant rates and pregnancy rates between the two groups (P>0.05). Conclusion: Our results indicate that the effective window of time for insemination by ICSI might be wider than previously thought, while we also noted that the higher miscarriage rate was obtained after the earlier injection in the fresh embryo transfer cycle of GnRH antagonist.

Key words: Sperm injections, intracytoplasmic, Fertilization in vitro, Embryo transfer, Gonadotropin-releasing hormone, OPU-ICSI interval