Estimation of the follicle-stimulating hormone (FSH) threshold for initiating the final stages of follicular development in women with elevated FSH levels in the early follicular phase

Abstract

To test the hypothesis that the follicle-stimulating hormone (FSH) threshold in patients with elevated FSH levels in the early follicular phase (EFP) is higher than in controls. Pilot study. Academic hospital. Six patients with elevated EFP FSH (>10 IU/L) and 13 controls. Treatment with a GnRH agonist in the midluteal phase before IV administration of recombinant FSH was started in an ultra-low-dose step-up protocol. The FSH threshold was determined by the mean of FSH levels of the above threshold value and the below threshold value. Follicle-stimulating hormone threshold, FSH screening value, E(2), number of follicles. The FSH threshold in the elevated EFP FSH group was 6.75 IU/L and was significantly higher than the FSH threshold of the controls (4.65 IU/L). The FSH screening value on day 3 was 12.0 IU/L in the patient group and 5.0 IU/L in the controls. Estradiol was significantly lower on the day that the largest follicle was 18 mm in the elevated EFP FSH group compared with controls (277 vs. 491 pmol/L, respectively). On the day of hCG administration, the number of smaller (10-13 mm) follicles was equal but the number of larger (>14 mm) follicles was higher in the control group compared with the elevated FSH group. In the control group, the basal FSH levels correlated highly with the FSH threshold levels (r = 0.8), but in the patients with elevated EFP FSH this correlation was absent. In normal women, basal FSH day 3 values represent the ovarian threshold for FSH. In women with elevated day 3 FSH, the FSH threshold is higher but not as high as basal FSH values. We postulate that the FSH threshold in patients with elevated EFP FSH is higher because of intraovarian factors. Basal FSH overshoots the threshold, probably because of the limited feedback by the ovary.