Estimating human ovarian non-growing follicle number: the application of modern stereology techniques to an old problem.

BACKGROUND Previous published reports on the number of non-growing follicles (NGFs) in the human ovary have employed model-based methods for number estimates. These methods are time-intensive, and require correction factors and assumptions that ultimately limit their accuracy. Here, we describe the modification, application and validation of a modern fractionator/optical disector technique for the estimation of human ovarian NGF number. METHODS Forty-eight pairs of normal human ovaries were collected from women (age 8-51 years) undergoing elective bilateral oophorectomy, organ donation, or from autopsy. After gross pathologic examination, systematic random sampling was utilized to obtain tissue for analysis by the fractionator/optical disector method. The precision of individual NGF counts was determined by calculating the observed coefficient of error (OCE). Intra-observer variability and variation in NGF number between ovaries within a pair were also determined. RESULTS The mean OCE was 16.6% with larger variations observed at lower follicle counts. In recount experiments of the same ovary, NGF number estimates varied by 15-29%, except at very low follicle counts where variation was greater, but absolute differences were small. There was no significant difference in NGF number between ovaries within a pair (Wilcoxon signed rank test, P = 0.81). CONCLUSIONS Modern stereology methods provide an unbiased, efficient method for estimating NGF number in the human ovary. Both ovaries within a pair contain similar numbers of NGFs.