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.