In your late 30s, your egg supply begins to decline in number and quality. As a result, your hormone production changes-you may notice a shortened menstrual cycle and some premenstrual syndrome (PMS) symptoms that you didn't have before.

Perimenopause

As your egg supply continues to decline, your ovulation and menstruation become irregular. This can start as early as your late 30s or as late as your early 50s. It continues for 2 to 8 years before menstrual cycles end. During this time, your ovaries are sometimes producing too much estrogen and/or progesterone and at other times too little. Your progesterone is likely to fluctuate more than before, which can lead to heavy menstrual bleeding. (If you have heavy or unexpected vaginal bleeding, see your health professional to be sure it is not caused by another, more serious condition.)

Menopause

About 6 months to a year before your periods stop, your estrogen starts to drop. When it drops past a certain point, your menstrual cycles stop. After a year of no menstrual periods, you are said to have "reached menopause."

Postmenopause

During the first year or so after menopause, estrogen levels continue to decline. It's normal to continue having symptoms, such as hot flashes or insomnia, during the first year or two after menopause. After your hormone levels reach a stable low point, these symptoms are likely to subside. Some women, however, continue to have symptoms for years, perhaps because their estrogen levels are particularly low. (After menopause, body fat tissue continues to produce estrogen. Women with low body fat tend to have lower estrogen levels.)

Low estrogen is part of the healthy, natural state of postmenopause. Low estrogen reduces your cancer risk (estrogen is linked to some types of cancerous cell growth). However, because it also plays an important role in skin and bone health, low estrogen creates some health concerns for the postmenopausal woman.

• Bone loss. Low estrogen levels after menopause speed bone loss, increasing your risk of osteoporosis in the future.
• Skin changes. Low estrogen leads to low collagen, which is a building block of skin and connective tissue. It's normal to develop thinner, dryer, wrinkled skin after menopause. The vaginal lining and the lower urinary tract also thin and weaken. This condition can make sexual activity difficult and can increase the risk of vaginal and urinary tract infections.
• Tooth and gum changes. Low estrogen affects connective tissue, which increases your risk of tooth loss and possibly gum disease.⁷

Although the reasons are not well understood, a woman's risk of heart disease increases after menopause. Because heart disease is the number one killer of women, consider your heart risk factors when making lifestyle and treatment decisions.