Density and distribution of primordial follicles in single pieces of cortex from 21 patients and in individual pieces of cortex from three entire human ovaries

BACKGROUND: At the time of cryopreservation of ovarian tissue for fertility preservation a small biopsy of ovarian cortex is usually taken for histological evaluation of the follicular reserve. The purpose of this study was to evaluate the distribution and density of primordial follicles in single pieces of cortex from individual patients and in pieces of cortex comprising entire ovaries, all prepared for cryopreservation. METHODS: Cortical biopsies from 21 patients and the whole cortex of one ovary were evaluated histologically prior to cryopreservation. In addition, the cortex of two whole ovaries was cryopreserved before histological evaluation. The volume of each cortical fragment was measured, all follicles counted and the follicular density calculated. RESULTS: In individual pieces of cortex follicular density showed a significant inverse linear correlation with age. The follicular density per cortical fragment prepared from each of the three entire ovaries varied from 1.8 to 166, 0.007 to 140 and 0.04 to 4.48 follicles/mm(3) cortical tissue. CONCLUSION: The density of primordial follicles varied more than two orders of magnitude in cortical fragments from each of the three ovaries. Primordial follicles were very unevenly distributed throughout the cortex of these ovaries, although a significant linear correlation between age and follicular density was found.