P-217 Keep calm and carry on: assessing the effect of below-benchmark vitrified/warmed donor oocyte survival rates in subsequent laboratory and clinical key performance indicators
Authors: Gallardo M , Goncalves I , Redondo J , Soares A  P , Garrido N , Metello J  L 
Published: July 2024

Abstract

Study question
When we experience below benchmark donor oocyte survival rates, are the laboratory and clinical outcomes of the recipient cycle affected?

Summary answer
Donor-oocyte cryo-survival rates below the benchmark (95-100%) result in slightly lower laboratory KPIs, equivalent live birth rates (LBR) and lower cumulative LBR (CLBR) per cycle.

What is known already
The use of vitrified/warmed donor oocytes allows overcoming many logistic challenges, but it is hindered by the loss of oocytes due to degeneration after warming. The 2012 Vienna Consensus established the benchmark rate of oocyte survival at 95-100%, competency level at &gt; 85%. Results of &lt; 85% cryo-survival are considered below competency, &lt;70% can be considered poor, and &lt;50% very poor. Below-benchmark rates of survival may not only limit the number of donor oocytes for the cycle, but they can also translate into lower per-oocyte cycle KPIs if the lower survival correlates with lower performance of the surviving oocytes.

Study design, size, duration
We analyzed 12690 vitrified-warmed donor oocyte recipient cycles, encompassing a total 144793 vitrified/warmed donor oocytes, carried out in a network of European private IVF units from 2018-2022. Cycles with PGT-A and spermatozoa from testicular biopsy were excluded. The primary endpoint of the study was the blastocyst utilization rate per 2PN zygote. Secondary endpoints were fertilization rate, live birth rate after the first single blastocyst transfer (SET-LBR) of each cycle, and cumulative LBR (CLBR).

Participants/materials, setting, methods
In all cases, fertilization was carried out by ICSI, and embryos were cultured to the blastocyst stage at low oxygen tension. Blastocysts with good or fair quality (A, B & C by ASEBIR Criteria) were considered usable (transferred + cryopreserved blastocyts / zygotes). Differences in proportions were analyzed using chi-square and the adjusted odds ratio (OR) was calculated using multivariable logistic regression.

Main results and the role of chance
Baseline donor and patient characteristics such as age, stimulation duration and dose, total donor oocytes per cycle, male factor, and fresh/frozen/donor spem were compared between groups and adjusted for when necessary.
The mean number of warmed oocytes per cycle was 11.4±3.22 with a mean survival rate of 89.2%. More oocytes per cycle were consumed in the lower survival groups, yet the total oocytes available for ICSI was smaller in the below competency, poor and very poor survival groups.
There were differences in the proportion of usable blastocysts per zygote amongst the survival rate groups (benchmark: 48.9%; competence: 47.0%, below-competence: 46.0%; poor: 43.6%; very-poor:43.6%, p &lt; 0.001).
Fertilization rates also differed between survival groups (benchmark: 76.9%; competence: 76.5%, below-competence: 75.6%; poor: 74.7%; very-poor:75.4%, p &lt; 0.001)
The adjusted odds ratio of live birth on the first SET of the cycle was not lower to the benchmark survival group in all the lower survival groups (Benchmark: 40.9%; Competence: OR:0.995; 95%CI:0.971-1.018; below-competence: OR:0.996; 95%CI:0.970-1.023; poor: OR:1.044; 95%CI:1.003-1.086, and very-poor: OR:1.069; 95%CI:0.976-1.170).
The CLBR decreased in lower survival groups, with 80.8% for the benchmark survival group, 80.3% (p = 0.539) for competence, 76.2% (p &lt; 0.001) for below-competence, 72.5% (p &lt; 0.001) for poor, and 74.8% (p = 0.056) for very-poor.

Limitations, reasons for caution
These results are limited to a donor-oocyte population.

Wider implications of the findings
Lower oocyte-cryo-survival rates resulted in a lower total number of usable blastocysts obtained for the recipient, and consequently, lower CLBR. However, the competence of surviving oocytes is encouraging, with laboratory KPIs in very close range irrespectively of the cohort survival rates, and similar implantation potential of the obtained blastocysts.

Trial registration number
not applicable