The reliability of ovarian function, both hormonally and reproductively, peaks in the mid-to-late twenties. Beginning in the early thirties, there is epidemiologic evidence of a decline in fertility. By the mid-thirties, there are subtle changes in the levels of FSH in the early follicular phase that become more marked in the forties. These changes may not be reflected in clearly noticeable changes in the experience of an individual woman’s menstrual cycle. As the mid-forties arrive, there may be a shortening of the length of the menstrual cycle that is a reflection of a declining pool of oocytes, declining inhibin, rising FSH and earlier efforts at recruitment and ovulation of the dominant follicle. The nature of these changes as perceived by an individual woman will be very different from person to person.
The perimenopause is defined as that period around the menopause that is marked by unpredictable ovarian function and menstrual irregularity. Epidemiologic studies of normal women suggest that this is a period of about four years around the menopause although the variation from woman to woman is large. This time is marked by unpredictable ovulation and periods of both higher and lower than usual estrogen levels. Uterine bleeding may be more or less than “usual” in flow and the timing of uterine bleeding is also unpredictable.
There are numerous physical and psychological phenomena attributed to this time of reproductive life (mood swings, vasomotor flushes, sleep disturbances, headaches, memory problems, decreased libido, and urinary incontinence). It is not clear which are related to fluctuations of ovarian function, which are related to aging, and which are psycho-social responses to mid-life which may vary from person to person and culture to culture.
The menopause is the retrospective diagnosis of the “final” spontaneous menstrual period. Usually a woman in her fifties who has not had a period for over a year may look back and note that her “menopause” was on a specific date of her last spontaneous period. The average age of menopause in American women is 51. Various inherited and environmental factors influence the age of menopause. Cigarette smoking, living at high altitude, exposure to some chemotherapeutic agents, and hysterectomy tend to slightly lower the age of menopause or final cessation of ovulation.
The climacteric is a term used for the transitional period including the perimenopause and the several years after the menopause. There are specific symptoms that some women may experience which are directly attributable to estrogen withdrawal (vasomotor flushes, urogenital atrophy), and there are some long-term aging and disease processes which are worsened by estrogen withdrawal (osteoporosis, coronary artery disease). There are number of other symptoms of aging which may be worsened by estrogen withdrawal (arthritis symptoms, cognitive function) but the evidence is not so clear.
The postmenopausal ovary is still capable of producing substantial amounts of weak androgens (ovarian stroma stimulated by menopausal levels of LH) that are peripherally converted to estrogens.