Aim: To compare different outcomes of vitrification and slow freezing of isolated pre-antral follicles and to evaluate different cryo-devices vitrification of isolated follicles.
Methods: pre-antral follicles were isolated from mouse ovaries and cryopreserved using vitrification and slow freezing. A preliminary was carried out to select the optimal cryo-devices vitrification of isolated follicles. A total of 414 follicles were randomly distributed among four groups: control (CT) fresh (n=100) , nylon mesh (n=96) , electron microscopy grid (n=120) , and micro-capillary tips (n=116) . Subsequetly, a total of 979 follicles were randomly assigned to three different group: CT fresh (n=256), vitrification (n=399) and
Slow freezing (n=324). CT and cryopreserved/thawed follicles were cultured in vitro and examined daily for development . final maturation was triggered with human chorionic gonadotrophin and rates of oocyte maturation were calculated. The Ultra-structure of cryopreserved / thwed follicles was studied using electron microscopy. Meiotic spindle presence and organization in mature oocytes were examined using the oosight imaging system.
Result: Micro-capillary tips resulted in poor immediate post-warming survival but no differences were observed in the subsequent in vitro development characteristics between different cryo-devices. Nylon mesh proved to be the easiest carrier, particularly when large numbers of follicles at the end of the culture period (P < 0.0001) However all other outcome measures were comparable between both techniques.
Conclusions: Isolated follicles were more vulnerable to cryodamage after slow freezing as compared to vitrification