Evidence is limited regarding the time intervals between human chorionic gonadotropin (hCG) administration and oocyte retrieval in controlled ovarian hyperstimulation cycles, and it is difficult to determine proper schedules to optimise outcomes for patients undergoing oocyte retrieval on the same day. We aimed to identify correlations between factors pertaining to treatment outcomes and time intervals to facilitate working schedules of ART centres. Our study included 2509 patients who underwent ICSI cycles. Based on different time intervals between hCG administration and oocyte retrieval, all cycles were divided into four groups: group 1 (34.00-35.99 hours), group 2 (36.00-36.99 hours), group 3 (37.00-37.99 hours) and group 4 (38.00-39.32 hours). Female age, basal FSH level, Gn starting stimulation dosage and total Gn dosage of group 1 were significantly higher than those of other groups. E2 level on hCG day and number of follicles aspirated were significantly higher in group 4 than in the other groups. Number of oocytes retrieved, oocyte retrieval rate, cleavage rate and number of usable embryos were positively correlated with the time interval, even after adjusting for female age, basal FSH level, E2 on hCG day and number of follicles aspirated. A fixed hCG administration time matching arranged oocyte retrieval is good enough for most patients to achieve maximal treatment outcomes. For patients with lower treatment expectations (expected no. of oocyte retrieval ≤3), moderately delayed oocyte retrieval would be more appropriate.Impact StatementWhat is already known on this subject? The time interval between hCG administration and OPU during COH is essential for ART treatment outcomes, but different intervals were reported in previous studies.What the results of this study add? Fixed hCG administration time matching arranged OPU is good enough for most patients to achieve maximal outcomes. For patients with lower treatment expectations (expected no. of oocyte retrieval ≤3), moderately delayed oocyte retrieval would be required.What the implications are of these findings for clinical practice and/or further research? We studied whether the oocytes and pregnancy outcomes changed along with extended time intervals, and there is no need to adhere to an exact interval for every patient. Therefore, it would help clinicians develop more reasonable time schedules for fertility centres and patients undergoing oocyte recovery on the same day.
Keywords: ICSI; hCG administration; oocyte retrieval; time interval.