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Menstruation and the Menstrual Cycle

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What is menstruation?

Menstruation is a woman's monthly bleeding, also called a period. When you menstruate, your body is shedding the lining of the uterus (womb). Menstrual blood flows from the uterus through the small opening in the cervix, and passes out of the body through the vagina. Most menstrual periods last from three to five days.

What is the menstrual cycle?

Menstruation is part of the menstrual cycle, which prepares your body for pregnancy each month. A cycle is counted from the first day of one period to the first day of the next period. The average menstrual cycle is 28 days long. Cycles can range anywhere from 21 to 35 days in adults and from 21 to 45 days in young teens.

Body chemicals called hormones rise and fall during the month to make the menstrual cycle happen.

What happens during the menstrual cycle?

In the first half of the cycle, levels of estrogen (the “female hormone”) start to rise and make the lining of the uterus (womb) grow and thicken. At the same time, an egg (ovum) in one of the ovaries starts to mature. At about day 14 of a typical 28-day cycle, the egg leaves the ovary. This is called ovulation.

After the egg has left the ovary it travels through the fallopian tube to the uterus. Hormone levels rise and help prepare the uterine lining for pregnancy. A woman is most likely to get pregnant during the three days before ovulation or on the day of ovulation. Keep in mind, women with cycles that are shorter or longer than average may ovulate earlier or later than day 14.

If the egg is fertilized by a man’s sperm cell and attaches to the uterine wall, the woman becomes pregnant. If the egg is not fertilized, it will break apart. If pregnancy does not occur, hormone levels drop, and the thickened lining of the uterus is shed during the menstrual period.

In the picture below, the egg has left the ovary and is on its way through the fallopian tube to the uterus.

diagram of the uterus

What is a typical menstrual period like?

During your period, the thickened uterine lining and extra blood are shed through the vaginal canal. Your period may not be the same every month and it may not be the same as other women's periods. Periods can be light, moderate, or heavy, and the length of the period also varies. While most periods last from three to five days, anywhere from two to seven days is normal. For the first few years after menstruation begins, longer cycles are common. A woman's cycle tends to shorten and become more regular with age. Most of the time, periods will be in the range of 21 to 45 days apart.

What kinds of problems do women have with their periods?

Women can have a range of problems with their periods, including pain, heavy bleeding, and skipped periods.

  • Amenorrhea – the lack of a menstrual period. This term is used to describe the absence of a period in:
    • young women who haven't started menstruating by age 15
    • women who used to have regular periods, but haven't had one for 90 days
    • young women who haven't had a period for 90 days, even if they haven't been menstruating for long

Causes can include pregnancy, breastfeeding, and extreme weight loss caused by serious illness, eating disorders, excessive exercising, or stress. Hormonal problems, such as those caused by polycystic ovarian syndrome (PCOS) or problems with the reproductive organs, may be involved. It is important to talk to a doctor.

  • Dysmenorrhea – painful periods, including severe cramps. When menstrual cramps occur in teens, the cause is too much of a chemical called prostaglandin. Most teens with dysmenorrhea do not have a serious disease even though the cramps can be severe. In older women, a disease or condition, such as uterine fibroids or endometriosis, sometimes causes the pain. For some women, using a heating pad or taking a warm bath helps ease their cramps. Some pain medicines available over the counter, such as ibuprofen (for instance, Advil®, Motrin®, Midol® Cramp), ketoprofen (for instance, Orudis® KT®), or naproxen (for instance, Aleve®), can help with these symptoms. If pain is not relieved by these medicines or the pain interferes with work or school, you should see a doctor. Treatment depends on what is causing the problem and how severe it is.
  • Abnormal uterine bleeding– vaginal bleeding that is different from normal menstrual periods. It includes very heavy bleeding or unusually long periods, periods too close together, and bleeding between periods. In both teens and women nearing menopause, hormonal changes can cause long periods along with irregular cycles. Even if the cause is hormonal changes, treatment is available. These changes can also go along with other serious medical problems such as uterine fibroids, polyps, or even cancer. You should see a doctor if these changes occur. Treatment for abnormal bleeding depends on the cause.

When does a girl usually get her first period?

In the United States, the average age is 12. This does not mean that all girls start at the same age. A girl can start her period anytime between the ages of eight and 15. Usually, the first period starts about two years after breasts first start to grow. If a girl has not had her first period by age 15, or if it has been more than two to three years since breast growth started, she should see a doctor.

How long does a woman have periods?

Women usually have periods until menopause. Menopause occurs between the ages of 45 and 55, usually around age 50. Menopause means that a woman is no longer ovulating (producing eggs) and can no longer get pregnant. Like menstruation, menopause can vary from woman to woman and these changes may take several years to occur. The time when your body begins its move into menopause is called the menopausal transition. This can last anywhere from two to eight years. Some women have early menopause because of surgery or other treatment, illness, or other reasons. If a woman doesn’t have a period for 90 days, she should see her doctor to check for pregnancy, early menopause, or other medical problems that can cause periods to stop or become irregular.

When should I see a doctor about my period?

You should see your doctor if:

  • you have not started menstruating by the age of 15, or by three years after breast growth began, or if breasts haven't started to grow by age 13
  • your period suddenly stops for more than 90 days
  • your periods become very irregular after having had regular, monthly cycles
  • your period occurs more often than every 21 days or less often than every 45 days
  • you are bleeding for more than seven days
  • you are bleeding more heavily than usual or using more than one pad or tampon every one to two hours
  • you bleed between periods
  • you have severe pain during your period
  • you suddenly get a fever and feel sick after using tampons

How often should I change my pad/tampon?

Pads should be changed as often as needed, before the pad is soaked with blood. Each woman decides for herself what works best. Tampons should be changed at least every four to eight hours. Make sure that you use the lowest absorbency tampon needed for your flow. For example, use junior or regular absorbency on the lightest day of your period. If you use a super absorbency tampon on your lightest days, you may have a higher risk for toxic shock syndrome (TSS). TSS is a rare but sometimes deadly disease. Young women may be more likely to get TSS. Using any kind of tampon, at any absorbency, puts you at greater risk for TSS than using pads. The risk of TSS can be lessened or avoided by not using tampons, or by alternating between tampons and pads during your period.

The Food and Drug Administration (FDA) recommends the following tips to help avoid tampon problems:

  • Follow package directions for insertion.
  • Choose the lowest absorbency for your flow.
  • Change your tampon at least every four to eight hours.
  • Consider alternating pads with tampons.
  • Know the warning signs of TSS (see below).
  • Don't use tampons between periods.

If you have any of these symptoms of TSS while using tampons, take the tampon out, and contact your doctor right away:

  • sudden high fever (over 102 degrees)
  • muscle aches
  • diarrhea
  • vomiting
  • dizziness and/or fainting
  • sunburn-like rash
  • sore throat
  • bloodshot eyes

For more information...

You can find out more about menstruation by contacting the National Women’s Health Information Center (NWHIC) at 1-800-994-9662 or the following organizations:

Food and Drug Administration
Phone Number(s): (888) 463-6332
Internet Address: www.fda.gov

American College of Obstetricians and Gynecologists (ACOG) Resource Center 
Phone Number(s): (800) 762-2264 x 192 (for publications requests only)
Internet Address: www.acog.org