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Small follicles in human ovaries were divided into 4 groups based on the morphological characteristics of the granulosa cells that surround the oocyte: B (flattened cells), B/C (mixture of flattened and cuboidal cells), C (one layer of cuboidal cells) and D (more than one layer of cells without epithelioid cells in the theca interna). On the basis of morphometric studies, including the number of granulosa cells in the largest cross-section, diameters of follicle, oocyte and germinal vesicle, folliculogenesis was categorized as in a dormant or growth phase. During the dormant phase, a transformation of follicles from Type B to Type C progressively took place. The growth phase started at an intermediary stage between large Type C and D follicles. The total ovarian follicular population and the numbers of each follicle type decreased significantly as age increased. The percentages of Type B follicles significantly decreased with increasing age whereas the percentages of Types B/C, C and D increased. In addition, there was a positive correlation between the percentages of Type B and a negative correlation between the percentages of Types B/C, C and D and the total ovarian follicular population. This last observation suggests the existence of an intra-ovarian regulation of the first steps of follicular growth.
Gougeon et al. (Sun,) studied this question.