Cohort size rather than follicle-stimulating hormone threshold level determines ovarian sensitivity in polycystic ovary syndrome.

The aim of the presented study was to compare FSH threshold levels and ovarian response to stimulation with one of two standard increments of exogenous FSH above the threshold in patients with polycystic ovary syndrome (PCOS) (n = 12) and eumenorrheic women (n = 11). The individual FSH threshold was determined by treatment according to a low-dose, step-up protocol with urinary FSH (Metrodin; Ares Serono, Geneva, Switzerland). In a subsequent treatment cycle, six PCOS patients and six eumenorrheic women were randomly assigned to double-blind treatment with the threshold dose plus 1/2 ampoule; the other six PCOS patients and five eumenorrheic women were treated with 1 ampoule above the threshold dose. Determination of threshold levels showed no significant differences in median and range between PCOS patients and eumenorrheic women. The number of follicles on the day of human chorionic gonadotropin administration showed no significant correlation with the increase in FSH level above the threshold level. Irrespective of the dose given, the number of follicles in the PCOS group was significantly higher than in eumenorrheic women. The higher sensitivity for gonadotropin stimulation in patients with PCOS compared with women with regular menstrual cycles therefore appears not to be dependent on differences in FSH threshold level, but rather on the larger size of the FSH sensitive cohort of small antral follicles.