Cryopreservation of human ovarian tissue using dimethylsulphoxide and propanediol-sucrose as cryoprotectants

Pieces of ovarian cortical tissue (0.3-2 mm in diameter) were obtained during gynaecological operations by biopsy or as a result of oophorectomy from 19 women aged 19-44 years. The tissue was frozen in a programmable freezer using one of two different cryoprotectants, either 1.5 M dimethylsulphoxide (DMSO), or a combination of 1,2-propanediol (1.5 M) and sucrose (0.1 M). After cryopreservation lasting from 24 h to 5 weeks, the ovarian pieces were thawed and studied histologically. Specimens taken before and after cryopreservation with either protectant showed no signs of tissue necrosis. Follicles at similar developmental stages were found before and after freezing. The proportions of follicles showing signs of atresia, 27% in the non-frozen tissue and 19% in the frozen-thawed tissue, were not significantly different. Oocytes, too, had the same appearance after freezing and thawing with both cryoprotectants as was seen in the specimens taken before freezing. These results suggest that cryopreservation of human ovarian tissue is feasible. However, the normality of the oocytes taken from tissue which has been frozen still needs to be established. Cryopreservation of ovarian tissue would be potentially an excellent method for storage of human oocytes once methods for their maturation in vitro have been developed.