P-187 Vitrified-warmed donor oocytes’ cryo-survival rate is not associated with subsequent embryological outcomes and clinical pregnancy rate per first transfer
Authors: Gallardo M , Braula A , Santos J , Castro M , Pedro M , Redondo J , Costa C , Hebles M , Soares A P , Sánchez-Martín F , Metello J L 
Published: June 2023

Abstract

Study question
Is the survival rate of a cohort of donor oocytes used for each recipient associated with the outcomes of the cycle?

Summary answer
Oocyte cryo-survival rates (benchmark = 95-100%, competency = 85-95%, below-competency = 70-85%, and poor = 50-70%) are not associated with embryological outcomes and clinical pregnancy in the first transfer of the 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 &lt;85% cryo-survival are considered below competency, and &lt;70% can be considered poor. Below-benchmark rates of survival may not only limit the number of oocytes, but also could translate into lower cycle KPIs.

Study design, size, duration
We analyzed 2190 vitrified-warmed donor oocyte recipient cycles, encompassing a total 20280 vitrified oocytes from 1036 donors. Cycles were carried out in 6 private IVF units from the same group. Cycles from 2018 to 2022 were included in the analysis. Cycles with PGT-A and spermatozoa from testicular biopsy were excluded. The outcome of the first transfer of each cycle was analyzed.

Participants/materials, setting, methods
Vitrification was performed using open carriers and two different commercial media (Irvine-Scientific and Kitazato). 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, and the usable blastocyst rate was the sum of all blastocysts transferred and cryopreserved, divided by the number of zygotes on day1.

Main results and the role of chance
The mean number of warmed oocytes per cycle was 9.3, with a survival rate of 93.7%. A pairwise comparison of fertilization rates with Bonferroni correction revealed that the benchmark survival rate group had similar results to the 85-95%, 70-85% and the 50-70% groups (95-100%: 73.7%; 85-95: 72.1%, 70-85%: 70.9%, 50-70%: 73.1%, p = 1 in all cases).
The usable blastocyst rate was similar between the benchmark survival rate and the 85-95% and 50-70% groups, but higher than the 70-85% group (95-100%: 49.0%; 85-95: 48.5%, p = 1.00; 70-85%: 43.5%, p = 0.012, 50-70%: 51.3%, p = 1.00).
Of 1368 Day5, SET, first-attempt transfers, 53.5% had a clinical pregnancy. The mean age of recipients undergoing embryo transfer was 42.6 ± 4.5 years and they had undergone 1.1 ± 1.8 previous IVF cycles. Adjusted-OR of clinical pregnancy was only significantly lowered in comparison to the benchmark survival rate in the 70-85% survival group (OR:0.49; 95%CI:0.34−0.71), but not it in the 50-70% group (OR:1.50, 95%CI: 0.92-2.46) nor the 85-95% group (OR:1.00, 95%CI: 0.70-1.42). The use of a sperm donor was positively correlated with clinical pregnancy (OR:1.39; 95%CI:1.04-1.88). Recipient age, male factor, and number of previous IVF cycles were not correlated with clinical pregnancy.

Limitations, reasons for caution
Retrospective study. Only open carriers were used for vitrification. Cumulative outcomes were not assessed.

Wider implications of the findings
Sub-benchmark levels of oocyte cryo-survival were not directly associated with worse laboratory outcomes or clinical pregnancy rates. These results are encouraging for cases with lower cryo-survival and useful to counsel patients in this regard. Nevertheless, striving to meet benchmark cryo-survival rates is essential.

Trial registration number
Not Applicable