Assessing the Effect of Below-benchmark Vitrified/warmed Donor-oocyte Survival Rates in Subsequent Laboratory and Clinical Outcomes

Objective: To assess the impact of below-benchmark (95%-100%) donor-oocyte survival rates on vitrification/warming in the laboratory and clinical outcomes of recipient cycles.

Design: Retrospective cohort study.

Subjects: We analyzed 12,690 vitrified-warmed donor-oocyte recipient cycles performed from 2018-2022.

Exposure: All cycles analyzed used exclusively vitrified/warmed donor oocytes. The cycles were grouped according to the survival rate experienced: benchmark 95%-100%; competence 85%-95%; below competence 70%-85%; poor 50%-70%; and very poor <50%.

Main Outcome Measures: The primary endpoint of the study was the total usable blastocyst rate per 2 pronuclear (2PN) zygote. Secondary endpoints were the fertilization rate, the live birth rate after the first single blastocyst transfer, and the cumulative live birth rate.

Results: The mean number of warmed oocytes per intracytoplasmic sperm injection (ICSI) cycle was 11.4 ± 3.2, with a mean survival rate of 89.1%. More oocytes per cycle were consumed in the lower survival groups, yet the total number of oocytes available for ICSI was smaller in the below-competence, poor, and very poor survival groups. The total usable blastocyst rate was lower in the lower survival groups (benchmark: 48.9%; competence: 47.0%, below competence: 46.0%; poor: 43.6%; and very poor: 43.6%), as well as the fertilization rates (benchmark: 76.8%; competence: 76.6%, below competence: 75.6%; poor: 74.7%; and very poor:75.5%). The adjusted relative risk (aRR) of live birth rate of the first embryo transferred was equal to the benchmark survival group in all the lower survival groups (benchmark: 40.9%; competence: aRR = 0.986, 95% confidence interval [CI]: 0.931-1.045; below-competence: aRR = 0.992, 95% CI: 0.929-1.059; poor: aRR = 1.103, 95% CI: 1.009-1.207; and very poor: aRR = 1.169, 95% CI: 0.963-1.419). The cumulative live birth rate decreased in lower survival groups compared with benchmark survival (benchmark: 79.2%; competence: aRR = 0.988, 95% CI: 0.961-1.015; below competence: aRR = 0.911, 95% CI: 0.880-0.944; poor: aRR = 0.802, 95% CI: 0.757-0.851; and very poor: aRR = 0.793, 95% CI: 0.693-0.907). The lower cumulative rates maintained in a subanalysis with equal metaphase-II available for ICSI (benchmark: 69.5%; competence: aRR = 0.909, 95% CI: 0.827-1.000; below competence: aRR = 0.942, 95% CI: 0.848-1.046; poor: aRR = 0.833, 95% CI: 0.7386-0.941; and very poor: aRR = 0.873, 95% CI: 0.695-1.097) CONCLUSION: Lower donor-oocyte cryo-survival rates have a moderate negative impact on the blastocyst utilization rate per 2PN zygote, fertilization rate, and the cumulative live birth rates of a donation cycle, even after adjusting for equal metaphase-II oocytes available for ICSI. Nonetheless, the surviving oocytes of a cohort seem to maintain a high competence level, with very similar laboratory outcomes, irrespective of the cohort's survival rates, as well as equal implantation potential of the resulting blastocysts.