What happens to hormones at menopause?

As women approach the menopause, menstrual cycles become irregular. The progressive shortening of the cycle is caused by shortening of the follicular rather than the luteal phase. About 25% of women aged 40-45 years and 40% in the 45-50 age group have anovulatory (infertile) cycles. The result of the increasing number of anovulatory cycles is unopposed estrogenic stimulation of the uterus which cause the thickening of the endometrium and often heavy and prolonged bleeds.

During the menopausal transition, hormonal levels are variable and unpredictable. All possible combinations of hormonal patterns can be observed during this phase. Therefore endocrine assessment of ovarian function is of poor predictive value with respect to timing of the menopause.

The first hormonal change is an increase of FSH concentrations in the early follicular phase which precedes alterations in menstrual pattern and estrogen concentrations. By 2- 3 years after the last menstrual period, serum FSH levels increase to values 10-15 times higher than follicular phase levels in young women and LH levels are about three times higher. The levels of both LH and FSH subsequently decrease with age.

Even in women with regular cycles there is a progressive decline in serum levels of Anti- Mullerian hormone and inhibin as a function of increasing age. Amh and inhibin concentrations are lower in women over 45 years of age than in younger women and undetectable after menopause. It seems that these hormones are reliable biomarker of the number and/or quality of follicles that remain in the ovary.

Some 20-40% of women have estrogen concentration consistent with the presence of functioning follicles in the first 6-12 months after final menstruation. By 12-24 months after menopause, estrogen levels fall into the postmenopausal (undetectable) range in most women. After the menopause quantitatively the most important circulating estrogen is estrone, which is formed by conversion of adrenal androgens, particularly androstenedione in fat tissue. Testosterone levels decline by about 20% and androstenedione by about 50%. In women who had surgically induced menopause (both ovaries removed surgically) the decrease in serum levels of both androgens is about 50%. After natural menopause in some women part of the ovary which normally produces male hormones undergoes hypertrophy resulting in increased capacity to produce these hormones. The level of DHEAS, which is mild androgen mainly of adrenal origin, declines linearly with age and is not specifically affected by the menopause.