Attaining dominance in vivo:: distinguishing dominant from challenger follicles in humans

This study provides the first report of local suppression of follicle growth in vivo by the dominant follicle in humans, Analyses were focused on antral follicles greater than or equal to 6 mm in diameter, classified as dominant (ovulatory) and challenger (large, non-ovulatory) follicles. We examined antral follicle characteristics, interactions and location in the ovary in the follicular phase of natural, ovulatory cycles in humans, Individual antral follicles (greater than or equal to 2 mm) were identified and monitored using a system, developed by the authors, incorporating mapping and computer modelling from ultrasound imaging of the ovary, Results showed that antral follicle development was not restricted to a particular location in the ovary, The apparent randomization of location may provide a developmental advantage for follicles, The population of challenger follicles peaked at mid follicular phase, suggesting a period when the ovarian environment was supportive of larger antral follicle development, As ovulation date approached, however, challenger follicles did not attain the visible characteristics of dominance: mid-level echogenicity, large size, smooth antral wall, round shape, Furthermore, dominant follicles subsequently appeared to reduce the number of neighbouring challenger follicles, The results strongly suggest that a paracrine secretion of the dominant follicle was the source of this localized effect, This process may provide increased nutrient level and space at a critical growth stage for dominant follicles.