Fig. 2

Histologic assessment of unfrozen, vitrified and slowly frozen human ovarian follicles. Sequentially hematoxylin and eosin stained human ovarian tissues from the unfrozen control (a), vitrification (b) and slow-freezing (c) groups. Tissues from the three groups are mainly composed of follicles at resting and primary stages. Well-preserved follicles exhibited intact nuclear and cellular membranes, uniform ooplasm and a prominent nucleus of the oocyte. Note two degraded follicles (black arrows) in the tissue cryopreserved according to the slow-freezing method (c), showing over 50 % oocyte detachment from surrounding GCs. Surrounding stroma in unfrozen tissue (a) and vitrified (b) tissues was compact, and stromal cells had spindle-shaped nuclei. Note increased numbers of pycnotic cells (black stars) and empty areas in the stromal tissue after slow-freezing (c). Scale bar = 20 μm