All women eventually enter menopause, also known as "the change" or climacteric, which marks the end of a woman's reproductive life. The stage you go through before actual menopause is called perimenopause, which takes place over about two to eight years (the average is four years) as the body undergoes its hormone-driven changes. This is the time when levels of estrogen, progesterone, and androgen start to decrease. The ovaries gradually stop releasing follicles (eggs), eventually ending your reproductive stage of life. As the body adjusts to this new stage, certain signs and symptoms can occur.

During perimenopause, you might start to experience some of the symptoms of menopause but still have menstrual periods. However, menstrual periods tend to become more and more irregular during this time. You've officially entered menopause when your doctor has confirmed that you're no longer ovulating (there's a special blood test to check this), or when you haven't had a single period in a whole year. Keep in mind that, unless your doctor tells you for sure, or until the full year is up, there's still a chance you can get pregnant.

Women are most likely to be between ages 40 and 60 years when they experience natural menopause - the average age is about 51. If you begin to go through menopause before the age of 40, it's called premature or early menopause. Menopause occurring after the age of 55 is considered a late menopause.

Some women experience induced menopause, which can happen for one of three reasons:

• Surgical menopause is triggered by having both ovaries removed during an operation. Women who have hysterectomies (removal of the uterus, therefore no menstrual periods) may or may not have their ovaries taken out, depending on how extensive the surgery was and why it was done.
• Chemotherapy-induced menopause is brought on by chemotherapy, usually in the course of being treated for cancer. These drugs can affect the ovaries enough to begin the process but, depending on different factors, chemotherapy-induced menopause isn't always complete or permanent.
• Radiation-induced menopause can happen while undergoing radiotherapy for cancer. If the ovaries are exposed to enough radiation, they'll begin to shut down.

The signs and symptoms of menopause - and how severe they are - vary so much from woman to woman that it's hard to know fully what to expect. Some women go through menopause with only a few hot flushes. Others feel most symptoms to the hilt. Some doctors say that the best guide to knowing how you'll be affected is to get your closest female relatives - mothers, aunts and grandmothers - to tell you about their experiences.

How can you tell if you're entering menopause? Some signs include:

• less frequent or erratic periods, which last for fewer days or have a lighter flow (although some women temporarily experience much heavier flows than usual during perimenopause)
• hot flushes (or flashes) - bursts of feeling extremely hot, accompanied by sweating - which can range from being mildly annoying to intensely uncomfortable (some women are awakened by night sweats that literally drench their sheets)
• insomnia or difficulty staying asleep
• mood changes
• vaginal dryness
• headaches
• difficulty concentrating
• urinary incontinence (leakage)

You should know that irregular bleeding, along with some of these symptoms, might be due to another cause. See your doctor to rule out other possible conditions.

Menopause is a very personal life event. Knowing what to expect can go a long way to easing any concerns or anxieties you may have about going through "the change." There's an upside, too: many women after menopause say that they've never felt better!