Observations in favor of normal early follicle development and disturbed dominant follicle selection in polycystic ovary syndrome.

Improved knowledge with regard to ovarian abnormalities in PCOS should help to classify patients suffering from this heterogeneous syndrome and may help to improve treatment outcome. Based on various observations, as previously discussed, it seems reasonable to assume that follicle development progresses to a size of 6-8 mm without an associated increase in estrogen biosynthesis. This is the size where dominant follicle selection takes place under normal conditions where follicle growth is arrested in polycystic ovaries. It may be hypothesized that under normal conditions FSH action is enhanced locally (for instance by changes in the IGF system) in the dominant follicle, whereas in polycystic ovaries this intraovarian upregulation is disrupted. Normal early antral follicle development is also confirmed by morphology studies. The classical concept of disturbed induction of the aromatase enzyme in PCOS should be questioned, since recent observations indicate that follicles may grow without a concomitant increased in intraovarian estrogens.