Should we worry about the clock? Relationship between time to ICSI and reproductive outcomes in cycles with fresh and vitrified oocytes

Is there an optimal time to perform ICSI with respect to the times of oocyte pick-up (OPU), in order to maximize the reproductive outcomes in cycles with fresh and vitrified/warmed donor oocytes? We found no significant differences in reproductive outcomes of ICSI cycles within a wide range of times between OPU and ICSI. In assisted reproduction, the oocyte is subject to denudation, vitrification/warming and ICSI. As shorter interaction with cumulus cells, oocyte ageing in vitro and insufficient recovery after warming may all impact the resulting embryo developmental competence, strictly controlled times between procedures are often implemented. However, most protocols have not been tested with the aim to improve reproductive results, and little information is available on the ideal times to be followed during these steps in order to optimize fertilization rates and embryo quality, and to achieve the highest pregnancy rate. Data from 3986 ICSI cycles performed between December 2012 and May 2014 were included (3178 with fresh and 808 with vitrified/warmed donor oocytes). ICSI was performed using donor oocytes and either partner or donor sperm. Exact times between OPU, denudation, vitrification, warming and ICSI were recorded automatically by a radiofrequency-based system. OPU was performed strictly 36 h after GnRH agonist trigger. Biochemical pregnancy was defined as a positive serum beta HCG 15 days after transfer, clinical pregnancy was defined as a visible embryo with heartbeat 5 weeks after transfer, and ongoing pregnancy was defined as a normally developing pregnancy at 12 weeks after transfer. Times between OPU and ICSI (OPU-ICSI) ranged from 1 h 25 min to 17 h 13 min (average(fresh) +/- SD = 4 h 58 m +/- 1 h; average(vitrified)= 9 h 18 m +/- 2 h). We found no effect of OPU-ICSI time on fertilization rate (p(fresh)=0.39; p(vitrified)=0.86) or embryo quality at Days 2 and 3 (p(fresh)=0.08; p(vitrified)=0.22). There was no difference in average OPU-ICSI times between positive and negative pregnancies (biochemical, clinical, ongoing and live birth rates) in either fresh (P = 0.71, 0.43, 0.79, 0.96) or vitrified (P = 0.59, 0.33, 0.73, 0.87) oocytes, respectively. Data were adjusted for oocyte donor age, semen status, number of motile spermatozoa and sperm concentration, and no effect of OPU-ICSI time on pregnancy and live birth rates for either fresh (P = 0.57, 0.16, 0.11, 0.46) or vitrified (P = 0.80, 0.73, 0.91, 0.95) oocytes was found. Further analysis for linear trend using OPU-ICSI time categorized in deciles showed that pregnancy rates and live birth rates do not increase or decrease across deciles. We found no effect of time taken for denudation to vitrification, warming to ICSI and denudation to ICSI on pregnancy rates. This is a study with automatically collected times from a high number of ICSI cases; however, its retrospective nature cannot exclude the influence of unaccounted for variables on the results. All oocytes came from oocyte donors (a parts per thousand currency sign35 years old), so results cannot be extended to older or infertile women. Our results indicate that the effective window of time for insemination by ICSI might be wider than previously thought. It therefore appears that, within appropriate time frames, the management of ICSI cycles involving oocytes from young women in embryology laboratories could be adjusted to accommodate caseloads and workflow with no loss of oocyte viability or cycle efficiency.