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

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

Keeping track of your menstrual cycles can help you understand what's typical for you. You also can record your ovulation and find important changes — such as a missed period or menstrual bleeding that isn't typical. While irregularities in your period usually aren't serious, sometimes they are caused by other health problems.

What's the menstrual cycle?

The menstrual cycle is the monthly series of changes the body goes through to prepare for pregnancy. Each month, one of the ovaries releases an egg. This is called ovulation. Hormonal changes at this time get the uterus ready for pregnancy. If the released egg isn't fertilized during ovulation, the lining of the uterus sheds through the vagina. This is a menstrual period.

What's typical?

The menstrual cycle is counted from the first day of one period to the first day of the next. The cycle isn't the same for everyone. Menstrual bleeding might happen every 21 to 35 days and last 2 to 7 days. For the first few years after menstruation begins, long cycles are common. However, menstrual cycles tend to shorten and become more regular as people age.

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

Certain kinds of birth control, such as extended-cycle birth control pills and intrauterine devices (IUDs), will change a menstrual cycle. Talk to your health care provider about what to expect.

When you get close to the time when your menstrual cycles will end, called menopause, your cycle might become irregular again. However, the risk of cancer of the uterus gets higher as you age. Talk with your health care provider about any irregular bleeding around menopause.

How can I track my menstrual cycle?

To find out what's typical for you, start keeping a record of your menstrual cycle on a calendar. Begin by tracking your start date every month for several months in a row to identify the regularity of your periods.

If you're worried about your periods, also track the following every month:

End date. How long does your period typically last? Is it longer or shorter than usual?
Flow. Record the heaviness of your bleeding. Does it seem lighter or heavier than usual? How often do you need to change your tampon or pad? Have you passed any blood clots?
Bleeding changes. Are you bleeding in between periods?
Pain. Describe any pain you have with your period. Does the pain feel worse than usual? It is not unusual to have some cramping or pain with your periods.
Other changes. Have you noticed any changes in your mood or behavior? Did anything new happen around the time you noticed changes in your periods?

What causes menstrual cycle irregularities?

Menstrual cycle irregularities can have many different causes, including:

Pregnancy or breast-feeding. A missed period can be an early symptom of pregnancy. Breast-feeding typically delays the return of your period after pregnancy.
Eating disorders, extreme weight loss or too much exercising. Eating disorders — such as anorexia nervosa — extreme weight loss and higher physical activity can interrupt your period.
Polycystic ovary syndrome (PCOS). People with this common disorder may have irregular periods. They also can have enlarged ovaries that contain small collections of fluid — called follicles — located in each ovary. These follicles can be seen during an ultrasound exam. People who have PCOS often have more follicles in the ovaries than other people.
Premature ovarian failure. Premature ovarian failure refers to the loss of typical ovarian function before age 40. People who have this condition, also known as primary ovarian insufficiency, might have irregular or occasional periods for years.
Pelvic inflammatory disease (PID). This infection of the reproductive organs can cause irregular menstrual bleeding.
Uterine fibroids. Uterine fibroids are growths in the uterus that are not cancer. They can cause heavy and prolonged menstrual periods.

What can I do to prevent irregularities?

Sometimes, birth control pills can help make an irregular menstrual cycle more regular. Birth control devices that contain progestin can make periods less heavy and ease cramping. Treatment for any problems that may cause these irregularities, such as an eating disorder, also might help. However, some menstrual irregularities can't be prevented.

In addition, talk with your health care provider if:

Your periods suddenly stop for more than 90 days — and you're not pregnant.
Your periods become irregular after having been regular.
You bleed for more than seven days.
You bleed more heavily than usual or soak through more than one pad or tampon every hour or two.
Your periods are less than 21 days or more than 35 days apart.
You bleed between periods.
You develop severe pain during your period.
You suddenly get a fever and feel sick after using tampons.

Remember, keeping track of your period can help you find out what's typical for you and what isn't. If you have questions or concerns about your menstrual cycle, talk to your health care provider.