Is There a Relation Between the Time to ICSI and the Reproductive Outcomes?

STUDY QUESTION: Does time to ICSI affect reproductive outcomes? SUMMARY ANSWER: Biochemical and clinical pregnancy diminish progressively as time between oocyte pick up (OPU) and ICSI increases after fresh embryo transfer. WHAT IS KNOWN ALREADY: Appropriate oocyte cytoplasmic and nuclear maturation are of paramount importance to ensure an optimal embryonic developmental competence. While nuclear maturation is usually attained by the time an oocyte reaches OPU, cytoplasmic maturation cannot be readily assessed and might be incomplete. On the other hand, excessive in vitro culture of mature human oocytes can affect their ultrastructural characteristics and, in mice, induces alterations in gene expression and changes of chromatin and histone modification patterns. STUDY DESIGN, SIZE, DURATION: Retrospective consecutive cohort study including 1468 ICSI cycles carried out in a single center between December 2012 and September 2015. All cycles were with patient's own oocytes and fresh embryo transfer (ET). A radiofrequency-based system was used to record exact culture times, namely, OPU-denudation (DN); DN-ICSI and OPU-ICSI. We analyzed the effect of total and partial time intervals between procedures, from OPU to ICSI, on fertilization rate and biochemical, clinical, ongoing pregnancy and live birth rates. PARTICIPANTS/MATERIALS, SETTING, METHODS: Differences in laboratory times between positive and negative biochemical, clinical, ongoing pregnancies and birth results were tested by Mann-Whitney U test. The likelihood of positive clinical outcomes was further modeled by locally weighted scatterplot smoothing (LOWESS) regression and logistic regression, adjusting for woman's age and BMI, number of transferred embryos; mean embryo morphological score, sperm origin and status, and number of mature oocytes obtained at OPU. Effect of time on fertilization rate was modeled by Generalized Linear Modeling (GLM) and LOWESS regression. MAIN RESULTS AND THE ROLE OF CHANCE: The mean woman's age was 38.4 years (SD 4.6). Biochemical, clinical, ongoing pregnancy and live birth rates after the fresh ET were: 39.6, 33.1, 25.7 and 20.8%, respectively. Cumulative values for biochemical pregnancy and live birth were 46.4 and 26.3%, respectively. Mean times in hours for OPU-DN, DN-ICSI and OPU-ICSI were: 1.00 (SD 0.20); 3.86 (SD 1.93) and 4.87 (SD 1.96), respectively, and were not different for pregnant and non-pregnant patients. However, multivariate analyses showed that on average (anti-log transformed), each 1-h increase in the OPU-ICSI time reduced the likelihood of biochemical pregnancy by 7.3% (95% CI: 0.7-13.5%) and of clinical pregnancy by 7.7% (95% CI 0.8-14.1%), after the fresh ET. No effect of time was observed for ongoing pregnancy or live birth rates. Increasing OPU-ICSI time increased the fertilization rate (B = 0.052, 95% CI: 0.022, 0.082). LIMITATIONS, REASONS FOR CAUTION: The lack of relationship between incubation time of oocytes and live birth rates might be due to uncontrolled variables. Given the population analyzed, these results should not be extended to other ART protocols such as in vitro maturation of oocytes or classical IVF fertilization. WIDER IMPLICATIONS OF THE FINDINGS: This study indicates that in vitro ageing of mature oocytes significantly affects the chances to become pregnant. Effect on live birth rates, although not evident in this study, cannot be excluded. Limiting incubation time of mature oocytes in the embryology laboratory should improve reproductive results for patients using their own oocytes and with a transfer of fresh embryos.