Successful cryoloop vitrification and subsequent in vitro maturation of mouse preantral follicles

The purpose of this study was to assess follicular viability and competence through in vitro maturation (IVM) of cryoloop vitrified mouse preantral follicles. Early mouse preantral follicles were isolated and vitrified using the cyroloop vitrification technique. After thawing, the preantral follicles and oocytes were cultured and in vitro matured for 10 d to the metaphase two stage (M2). Oocytes were assessed for viability at 2 and 10 d of IVM and compared to a control group of freshly isolated preantral follicles undergoing IVM. Of vitrified follicles, 94.0% (345/367) were recovered after thawing. The survival rate after the first two-days of IVM culture was 82.3% (284/345) for the cryoloop vitrified follicles and 100% for the control follicles (437/437). The percentage of oocytes in the cryoloop group that developed to M2 was 70.2% (174/248), comparable to that of the control group at 68.7% (241/351) (p value 0.12). Our results indicate that cyroloop vitrification is a viable and practical technique for cryopreservation of mouse preantral follicles. Human oocyte cryopreservation by means of cryoloop vitrification may prove to be useful as a possible treatment modality for human fertility preservation.