O-205 Application of a single “Universal warming protocol” for vitrified donor oocytes: A prospective, multicenter study
Authors: Troncoso-Perez P , Zavala-Garcia A , Gonzalez-Navas C , Sosa-Rosales D F , Criado-Scholz E 
Published: June 2022

Abstract

Study question
Is it possible to use different commercial thawing kits with donor oocytes that have been vitrified with a Kitazato vitrification kit?

Summary answer
The Omni thawing kit showed higher survival rates of donor oocytes. However, fertilization, blastulation, and chemical pregnancy rates were similar in all three thawing kits.

What is known already
Vitrification is the best method for cryopreserving metaphase II (M2) oocytes and blastocysts. Oocyte vitrification and subsequent thawing is performed with the use of different commercial kits. Currently, the thawing kit usually corresponds to the same provider as the vitrification kit used. However, this may create issues when using cryopreserved oocytes among different clinics with different vitrification kits and, furthermore, not all lab professionals are accustomed to using other commercial kits. Using a “single warming protocol” would provide a solution to these drawbacks and would improve the compatibility of exchanging gametes and embryos among collaborating centers.

Study design, size, duration
This is a longitudinal, comparative and prospective study conducted between January 2017 and December 2020 at four different IVF private centers. Overall, we vitrified a total number of oocytes (n = 2172) with a single Kitazato commercial vitrification kit at a Spanish Egg Bank, and three independent IVF centers used different thawing kits (Kitazato, Irvine or Omni) as a warming protocol.

Participants/materials, setting, methods
The study included oocytes from altruistic anonymous egg donors aged 18-35 years, subject to the rigorous standards to become an oocyte donor. The primary outcome was survival and fertilization rate; secondary outcomes included blastulation rate, and chemical pregnancy rate.

Main results and the role of chance
A total of 2172 M2 oocytes were retrieved and subsequently vitrified using the Kitazato protocol and the Cryotop device. All vitrified donor M2 oocytes were thawed at independent assisted reproduction centers using the following thawing kits: Omni Vitrolife (n = 655), Kitazato (n = 1021), and Irvine (n = 496). Oocytes thawed using the Omni kit had a 94% (617/655) survival rate and a 73% fertilization rate. Kitazato thawing kits had an 86% (877/1021) survival rate and a 77% fertilization rate. Lastly, Irvine thawing kits had an 85% (423/496) survival rate and a 74% fertilization rate. Survival rate results were statistically significant among different thawing kits (P-Value = &lt;0.01). Fertilization rates were not statistically significant. Blastulation rates with Omni, Kitazato and Irvine thawing kits were 57%, 52%, and 58%, respectively (Not statistically significant). Lastly, chemical pregnancy (HCG-Beta positive) rates with Omni, Kitazato and Irvine thawing kits, results were 65%, 54%, and 76%, respectively (Not statistically significant).

Limitations, reasons for caution
The study was carried out in centers with long experience collaborating together, but many different professionals intervened in the process, without the same conditions in all labs.

Wider implications of the findings
With increasing requirements for cryopreserved oocytes due to the difficulties of donor-recipient synchronization, popularization of treatments from abroad, and the need to import or send donor oocytes for recipient phenotypes, it has become of paramount importance to use a single universal warming protocol irrespective of cryopreservation kits.

Trial registration number
NOT APPLICABBLE