What the heck is Premenopause, Perimenopause and Postmenopause?

As defined by the World Health Organization, menopause is the permanent cessation of menstruation due to the loss of ovarian follicular activity . This definition uses both a symptom that can be identified by a woman (the end of menstruation) and a sign that can be measured (the loss of follicular activity results in changes in levels of hormones). Investigators have generally agreed to define menopause as the last menstrual period followed by at least twelve months of amenorrhea (no menstrual bleeding). The advantage of this definition is that it identifies a single, measurable variable within the climacteric transition. This definition makes it possible to compute median or mean ages at menopause for inter- and intrapopulation comparisons. The definition also allows one to delineate a clinically normal range in age at menopause (for example, ages forty to sixty). Finally, this definition enables clinicians to identify
women who are postmenopausal for medical “management.” But while thelast menstrual period is a clinically useful marker of an event, the average woman’s sense of the process of the menopausal transition is better described by the term “perimenopause,” a gray, difficult-to-define time period during which a woman wonders if each period of bleeding is the last.

K. I know thats too complicated so take this:

Stages and Definitions of the Menopause Transition

Premenopause: Regular cycling. Having experienced a menstrual period
during the two months prior to study.

Perimenopause: Irregular cycling. Having experienced a menstrual period
from three to eleven months prior to study.

Postmenopause: Having experienced the last menstrual period at least
twelve months prior to study

That said, women still perceive menopause to be a marker for the end of childbearing because most women have no other “window” into the state of their ability to conceive. The end of menstruation can, therefore, be an emotionladen event. Some women react to the cessation of menstruation with relief (no more birth control); others describe deep sadness because they can no longer bear children.

My thoughts on Menopause

There are three questions driving my interest in menopause:
Why did menopause evolve?
Why do some women experience menopause at forty-two, while others cycle like clockwork to the age of fifty-eight?
Why does menopause pass unnoticed for some women, while others suffer from unrelenting hot flashes?

Oh! sorry. Its not over I got some other 'SERIOUS' questions too;
Why do human females close down childbearing long before the end of life, while most chimpanzees reproduce until shortly before death?
Why didn’t my mother have any hot flashes, while other women remove strategic layers of clothing and visibly sweat?

Bring up the topic of menopause, and I’m more than happy to contribute curious observations, interesting hypotheses, and leaps of biological faith. Yet there are so many questions that I can’t answer. Friends and colleagues at work ask, “I can’t remember names anymore. Is that menopause?” “My left arm goes numb. Is that menopause?” “I want to have sex twice a day. Is that menopause?” “I’m more depressed than I have ever been. Is that menopause?”

Variation in age at menopause and in symptom experience can be understood
at the level of the population by combining a familiarity with biology with observations of cultural difference. I have summarized much of what is known across a wide variety of populations, including those that are most familiar to me: upstate New York (where women talk about menopause as something natural, ordained by God), western Massachusetts
(where women proactively smear themselves with yam cream and eat blue-green algae for menopausal health), Puebla, Mexico (where marital stress is a constant topic of concern among women of menopausal age), the Selsa ka Valley, Slovenia (where menopause is an uncomfortable, taboo topic of conversation), and Asunción, Paraguay (where some women describe menopause as un alivio, a relief, but others volunteer the word desesparación, despair, as a menopausal symptom).

I focus on menopause both as a onetime event, the last menstrual period, and as an ongoing process, the transition from pre- to postreproductive life. These two points of view—event and process—reflect different approaches to the study of menopause, and both are necessary. I also examine the evolution and contemporary experience of menopause in a particular way—from a biocultural perspective.