Menopause is actually defined as the period beginning twelve months after a woman’s last menstrual cycle. this is the point when a woman is not “going through” menopause but is “in” menopause.
Therefore, the Menopause as the term used to describe the time women stops having her menstrual periods is actually, is more commonly (and inaccurately) used to describe only one menopause stage, perimenopause. There are stages of menopause which women experience. These stages of menopause consist of:

• Premenopause
• Perimenopause
• Menopause
• Postmenopause

The timeline below illustrates the stages of menopause in relation to age. this is a representation of the number of years for each menopause stage that may help in understanding the stages of menopause. Each stage is described below in more details.

Definitely, the stages of menopause depend upon the reason for which the onset of menopause occurred. when menopause is induced by a surgical procedure or by radiation or drug therapy that causes damage to the ovaries, then the stages of menopause are different than those associated with natural menopause which occurs in all women, usually in the fifth decade of life.
The first stage, premenopause, as well as the last stage, postmenopause, last the longest. By dividing menopause into separate stages, it is easier to identify and address the health issues and symptoms unique to each.
Premenopause
This first stage lasts from the onset of menstruation to the last normal period. it is during her reproductive years that menopause may be the furthest thing from a woman’s mind. for most women, this stage begins at 10 to 16 years of age, when the first period occurs, to the last normal period, which usually occurs in a woman’s 40s or 50s.

You may notice in the literature that this term is often misused to describe the years immediately before menopause (perimenopause) and also to describe premature menopause.

It is during this initial stage of menopause that young women can lay the foundation for good health in later years through good nutrition and exercise.
Perimenopause
This stage is often the most stressful time for women. the menstrual cycle may become irregular before it ceases completely. Menstrual flow may become lighter or heavier. Each missed period raises questions about whether a woman is pregnant or entering menopause.
This stage, which lasts from 2 to 10 years, is often characterized by irregular menstruation with occasional missed periods. Until menses stop completely, it is still possible to become pregnant.
When discussing menopause, most women refer to perimenopause because it’s during this stage that the hormone levels change and levels of estrogen decline. as ovarian production decreases, the follicle stimulating hormone (or FSH) increases, triggering symptoms like hot flashes, headaches, memory problems, acne, mood swings, night sweats, and insomnia. low estrogen levels may cause vaginal dryness and irritation.

Your period could go in any direction during this transitional time. your flow may be heavier than normal; it may be lighter than normal; your period could come at closer intervals, and it may come at longer intervals. Some women have spotting between periods. You may have shorter periods of bleeding than normal, or you may have longer periods of bleeding than normal.
Perimenopause typically takes place between 45- and 60-years-of-age. Early signs of perimenopause usually occur in a women in mid 40-s. it was noticed, that women who experience early menopause typically follow their mothers pattern.
While changes in the menstrual pattern are common during this time, women should maintain a dialogue with their doctor because frequent or heavy bleeding needs to be evaluated further.
Menopause
Menopause occurs when a woman does not have her period for 12 months, starting from the day when a woman has her last period. this is actually the shortest stage and the only one with a defined length. If a woman skips several menses and then they return, the clock starts again. it is retrospective. Women do not know they are in menopause until 1 year without a period passes (some specialists claim that menopause can be defined by more than 6 consecutive period-free months, however there are cases, when menstruations return after 6-months period, announcing that menopause has not started yet). only after the confirmed “waiting period” they look back and realize they are in menopause. this can be a time of mixed emotions for many women as the childbearing years are over, children are grown and retirement beckons.
Menopause is the permanent termination of menstruation and fertility. this stage begins when a woman has her last period. this stage, ovaries no longer produce eggs as hormone production stops, and common changes become noticeable – including vaginal dryness and loss of sex drive.
Postmenopause
Postmenopause begins 12 months after the last period and lasts until death. With women’s increased life expectancy, the postmenopausal stage is a relatively new stage of life. A woman’s life expectancy has increased from 48 years in 1900, to 80 years in 2005, according to the U.S. Centers for Disease Control and Prevention’s publication: Health, United States, 2008. the majority of women did not live to the postmenopausal years in the early 1900s. Today they often enjoy an active lifestyle into their 70s and 80s.

Generally by this stage, most menopausal symptoms have ceased. Vaginal atrophy, which is due to low, rather than fluctuating, estrogen levels, may persist. Postmenopausal women with low estrogen may be at increased risk for osteoporosis and should consume adequate calcium and vitamin D and have a screening test for low bone density.

Sources and Additional Information:
menopause-natural.com/menopause_stages.htmlmenopause-black-cohosh.org/articles-menopause/stages.htmllivestrong.com/article/88924-menopause-stages/menopauseinsight.com/menopause/stages-of-menopause.aspxmenopause-faq.com/menopause-stages.htm