The rest of the follicles gradually shrink in size, resulting in a decrease in ovarian mass from 14 grams before menopause to 5 grams after. As ovaries age, follicles secrete less estrogen and progesterone, and perimenopause begins. FSH stimulates development of follicles, and LH stimulates follicular production of estrogen, ovulation, and formation of the corpus luteum, the body within a ruptured follicle that secretes progesterone. For a while, the pituitary hormones maintain near-normal homeostasis, but as time passes, the increased amounts of FSH and LH can no longer stimulate sufficient production of estrogen and progesterone. Perimenopause is marked by waning ovarian function, inconsistent follicular development, and finally, complete cessation of ovulatory function.
Monthly periods become irregular and eventually stop.
Transitional years The perimenopausal years are those preceding menopause during which women transition from regular to irregular cycles. Women experience symptoms reflecting extreme hormonal fluctuations. The average age of menopause in American women is 51. 6 Perimenopause lasts two to eight years, averaging four for most women. Because women may still have regular periods at first, they may not realize the changes they're experiencing are due to perimenopause.