The hormonal transitions in a woman’s life are like a long rollercoaster ride. During the preteen or early teen years, your ovaries respond to signals from your brain and begin producing the hormones estrogen, progesterone, and testosterone. Soon after, monthly ovulation begins (release of an egg from the ovary), followed by a menstrual period if the egg is not fertilized by sperm.
For about 25 years, from your early teens to age 40, you tend to be most fertile. Levels of the hormones estrogen and progesterone rise and fall in a predictable rhythm, triggering monthly ovulation and regular menstrual periods. At some point during your 40s, though, things start to change. As the ovaries age, they may not release an egg every month, and the female hormones tend to rise and fall in less predictable patterns. Estrogen and progesterone levels can spike very high and then fall quite low. Your periods may be heavier or more frequent, or lighter or less frequent. You may start to experience some of the symptoms associated with menopause, such as mood changes, hot flashes, vaginal dryness, or trouble sleeping. This time of transition is called perimenopause, and it can last anywhere from 2 to about 10 years.
Eventually, hormone levels even out to consistently low levels, eggs are no longer released, and periods stop completely. Once you have gone 12 consecutive months without a period, you are officially through menopause and no longer fertile.
Every woman experiences menopause a little bit differently. Some women have fairly mild symptoms and a gentle transition, while others have more intense and bothersome symptoms. Your experience may depend on how quickly you move from perimenopause to menopause. A quick transition may give your body less time to adapt to changing hormone levels. Your experience also may depend on how much estrogen your body has from other sources besides the ovaries. After menopause, your fat tissue and muscle tissue make a form of estrogen called estrone, which is weaker than that made by the ovaries—but if you have more of it, the transition to menopause may go more smoothly. These are just two possibilities, though: We often can’t explain why one woman breezes through menopause while another has every symptom imaginable.