Menstrual cycle: What's normal, what's not

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Do you know when your last menstrual period began or how long it lasted? If not, it might be time to start paying attention.

Tracking your menstrual cycles can help you understand what's normal for you, time ovulation and identify important changes — such as a missed period or unpredictable menstrual bleeding. While menstrual cycle irregularities usually aren't serious, sometimes they can signal health problems.

The menstrual cycle is the monthly series of changes a woman's body goes through in preparation for the possibility of pregnancy. Each month, one of the ovaries releases an egg — a process called ovulation. At the same time, hormonal changes prepare the uterus for pregnancy. If ovulation takes place and the egg isn't fertilized, the lining of the uterus sheds through the vagina. This is a menstrual period.

The menstrual cycle, which is counted from the first day of one period to the first day of the next, isn't the same for every woman. Menstrual flow might occur every 21 to 35 days and last two to seven days. For the first few years after menstruation begins, long cycles are common. However, menstrual cycles tend to shorten and become more regular as you age.

Your menstrual cycle might be regular — about the same length every month — or somewhat irregular, and your period might be light or heavy, painful or pain-free, long or short, and still be considered normal. Within a broad range, "normal" is what's normal for you.

Keep in mind that use of certain types of contraception, such as extended-cycle birth control pills, will alter your menstrual cycle. Talk to your health care provider about what to expect.

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