Throughout the menopausal transition, some subtle — and some not-so-subtle — changes in your body may take place. You might experience:

• Irregular periods. As ovulation becomes more unpredictable, the length of time between periods may be longer or shorter, your flow may be light to heavy, and you may skip some periods. If you have a persistent change of seven days or more in the length of your menstrual cycle, you may be in early perimenopause. If you have a space of 60 days or more between periods, you're likely in late perimenopause.
• Hot flashes and sleep problems. Hot flashes are common during perimenopause. The intensity, length and frequency vary. Sleep problems are often due to hot flashes or night sweats, but sometimes sleep becomes unpredictable even without them.
• Mood changes. Mood swings, irritability or increased risk of depression may happen during perimenopause. The cause of these symptoms may be sleep disruption associated with hot flashes. Mood changes may also be caused by factors not related to the hormonal changes of perimenopause.
• Vaginal and bladder problems. When estrogen levels diminish, your vaginal tissues may lose lubrication and elasticity, making intercourse painful. Low estrogen may also leave you more vulnerable to urinary or vaginal infections. Loss of tissue tone may contribute to urinary incontinence.
• Decreasing fertility. As ovulation becomes irregular, your ability to conceive decreases. However, as long as you're having periods, pregnancy is still possible. If you wish to avoid pregnancy, use birth control until you've had no periods for 12 months.
• Changes in sexual function. During perimenopause, sexual arousal and desire may change. But if you had satisfactory sexual intimacy before menopause, this will likely continue through perimenopause and beyond.
• Loss of bone. With declining estrogen levels, you start to lose bone more quickly than you replace it, increasing your risk of osteoporosis — a disease that causes fragile bones.
• Changing cholesterol levels. Declining estrogen levels may lead to unfavorable changes in your blood cholesterol levels, including an increase in low-density lipoprotein (LDL) cholesterol — the "bad" cholesterol — which contributes to an increased risk of heart disease. At the same time, high-density lipoprotein (HDL) cholesterol — the "good" cholesterol — decreases in many women as they age, which also increases the risk of heart disease.

As you go through the menopausal transition, your body's production of estrogen and progesterone rises and falls. Many of the changes you experience during perimenopause are a result of decreasing estrogen.

Menopause is a normal phase in life. But it may occur earlier in some women than in others. Although not always conclusive, some evidence suggests that certain factors may make it more likely that you start perimenopause at an earlier age, including:

• Smoking. The onset of menopause occurs one to two years earlier in women who smoke than in women who don't smoke.
• Family history. Women with a family history of early menopause may experience early menopause themselves.
• Cancer treatment. Treatment for cancer with chemotherapy or pelvic radiation therapy has been linked to early menopause.
• Hysterectomy. A hysterectomy that removes your uterus, but not your ovaries, usually doesn't cause menopause. Although you no longer have periods, your ovaries still produce estrogen. But such surgery may cause menopause to occur earlier than average. Also, if you have one ovary removed, the remaining ovary might stop working sooner than expected.

Irregular periods are a hallmark of perimenopause. Most of the time this is normal and nothing to be concerned about. However, see your doctor if:

• Bleeding is extremely heavy — you're changing tampons or pads every hour or two for two or more hours
• Bleeding lasts longer than seven days
• Bleeding occurs between periods
• Periods regularly occur less than 21 days apart

Signs such as these may mean there's a problem with your reproductive system that requires diagnosis and treatment.