Comparing the viability and in vitro maturation of cumulus germinal vesicle break down (GVBD) oocyte complexes using two vitrification techniques in mice

Background: vitrification is assumed to be a promising method to cryopreserve humanoocytes but still needs optimizing.objective: the aim of this study was to improve the single step and step-wisevitrification effects on maturing mouse gvbd oocytes by ethylene glycol (eg) inconventional straws.materials and methods: oocytes with compact cumulus cells were cultured for 3hr intcml99 supplemented with 10% fetal bovine serum (fbs) in 5% c02 in air. gvbdoocytes were randomly allocated into three groups. (1) control (non-vitrified group), (2)exposed to single-step vitrification (contained of eg 20%+0.5m sucrose), (3) exposedto step-wise vitrification (2%, 5%, 10%, 20%eg +o.5m sucrose). in vitrificationgroups,oocytes were thawed and underwent additional 21 hr maturation. viability ofoocytes and maturation to mil stage were analyzed using inverted microscope andadditionally by staining ofpropidium iodide and hoechst 33342 .results: all non-vitrified oocytes were viable after 24 hr; however, viability of vitrifiedsamples in single-step group was significantly lower than that of the step-wise andcontrol groups. also, the maturation rate in the step-wise group was significantly higher(p < 0.05) compared to single-step.conclusion: these results suggest that step-wise vitrification of gvbd oocytes ascompared to single step vitrification was better in the rate of survival and in vitromaturation of oocytes.