The Endocrinology of Menopause

The ovary contains the maximum number of ovarian follicles during fetal life. By the time menopause approaches, the number of ovarian follicles has decreased substantially, and those present respond poorly to FSH and LH. As a result, cycle irregularity develops because of erratic ovulation.(16,17) As follicular development declines, the cyclical fluctuations in estrogen and progesterone are lost, and circulating levels of these hormones decrease.

In the normal ovarian cycle, circulating serum estradiol levels fluctuate from 40 pg/mL in the early follicular phase to 200-400 pg/mL at midcycle and 100 pg/mL during the luteal phase.(18) Postmenopausal women, however, have very low serum estradiol levels (Figure 6). At the same time, FSH increases dramatically (Figure 7). FSH levels >30 mIU/mL are a strong indication that a woman is menopausal.