vitrification of human germinal vesicle oocytes; before or after in vitro maturation?

background: the utilization of immature oocytes derived from stimulated cycles could be of great importance, specially for urgent fertility preservation cases. the aim of the current study was to determine whether in-vitro maturation is more successful before or after the vitrification of these oocytes. materials and methods: the study was performed in a private ivf center. 318 germinal vesicle (gv) stage oocytes were collected from 104 stimulated oocyte donation cycles. oocytes were divided into two groups according to whether vitrification was applied at the gv stage (group 1) or if they were in vitro matured to the mii stage and then vitrified (group 2). in a third, control group, oocytes were in vitro matured without being vitrified (group 3). in all three groups, survival rate after warming, maturation rate and mii-spindle/chromosome configurations were assessed. chi-square test was used to compare rates between the three groups. statistical significance was defined at p<.05 while bonferroni criterion was used to assess statistical significance regarding the various pairs of groups. statistical package for social science 17.0 was used to perform statistical analysis. results: no significant difference was observed in the survival rate after vitrification and warming of gv and mii oocytes (93,5% vs. 90,8% respectively). the maturation rate was significantly higher when ivm was performed before vitrification (82,9% vs. 51%). there was no significant difference in the incidence of normal spindle/chromosome configurations among warmed oocytes matured in vitro before or after vitrification (50,0% vs. 41,2% respectively). however, the incidence of normal spindle/chromosome configurations was higher in in-vitro matured oocytes which were not subjected to vitrification (fresh oocytes) (77,9%). conclusion: in stimulated cycles, vitrification of in vitro matured mii oocytes rather than gv oocytes seems to be more efficient. this approach needs to be verified in non-stimulated fertility preservation cases.