Ultra-fast vitrification and rapid elution of human oocytes: part I. germinal vesicle model validation

RESEARCH QUESTION: Can GV-oocytes serve as an effective model to test the efficacy of ultra-fast vitrification (UFV)/ rapid elution (RE) treatments to support reliable, high survival rates and sustained functionality? DESIGN: Prospective pilot cohort studies were performed to investigate the feasibility of non-equilibration, UFV to sustain cellular integrity and development in contrast to control vitrification (CV: 10-15min ES/ 1min VS). In Phase 1, we applied a 2 × 2 factorial design (n=25-30 eggs/group) to evaluate post-warming dilution treatments: conventional multi-step (CD) versus rapid elution (RE; one-step), including an apriori fresh egg control group. Phase 1/2 focused on survival and maturation assessments, including meiotic spindle formation (Phase 2). RESULTS: The survival of EG/DMSO treated UFV oocytes in Phase 1 and 2 was not different to spontaneous degeneration seen in the fresh IVM control groups (3.2%) but was higher than CV treated oocytes immediately post-warming (p<0.03). Of the intact GVs, no difference in IVM-MII development was detected (52.6 -58.3%) at +48h IVM across all groups. Meiotic spindle integrity of MII oocytes was normal in all treatment groups. CONCLUSIONS: As originally reported by Gallardo (2019), non-equilibrated dehydrated human oocytes can effectively vitrify after UFV/CD treatment. We further verified the resiliency of oocytes to withstand RE treatment and continue to develop normally, like fresh GV-matured oocytes. Furthermore, we confirmed that the meiotic spindle formation and density of UFV/RE-treated GV oocytes was similar to fresh controls. Overall, the GV-model proved to be a useful resource to substantiate the promising potential of UFV technology to reliably achieve high survival and normal developmental competence in a more time efficient manner.