Topic Overview

What is a menstrual cycle?

The menstrual cycle is the series of changes a woman's body goes through to prepare for a pregnancy. About once a month, the uterus grows a new lining (endometrium) to get ready for a fertilized egg. When there is no fertilized egg to start a pregnancy, the uterus sheds its lining. This is the monthly menstrual bleeding (also called menstrual period) that women have from their early teen years until menopause, around age 50.

The menstrual cycle is from Day 1 of bleeding to Day 1 of the next time of bleeding. Although the average cycle is 28 days, it is normal to have a cycle that is shorter or longer.

Girls usually start having menstrual periods between the ages of 11 and 14. Women usually start to have fewer periods between ages 39 and 51. Women in their 40s and teens may have cycles that are longer or change a lot. If you are a teen, your cycles should even out with time. If you are nearing menopause, your cycles will probably get longer and then will stop.

Talk to your doctor if you notice any big change in your cycle. It's especially important to check with your doctor if you have three or more menstrual periods that last longer than 7 days or are very heavy. Also call if you have bleeding between your periods or pelvic pain that is not from your period.

What controls the menstrual cycle?

Your hormones control your menstrual cycle. During each cycle, your brain's hypothalamus and pituitary gland send hormone signals back and forth with your ovaries. These signals get the ovaries and uterus ready for a pregnancy.

The hormones estrogen and progesterone play the biggest roles in how the uterus changes during each cycle.

• Estrogen builds up the lining of the uterus.
• Progesterone increases after an ovary releases an egg (ovulation) at the middle of the cycle. This helps the estrogen keep the lining thick and ready for a fertilized egg.
• A drop in progesterone (along with estrogen) causes the lining to break down. This is when your period starts.

A change in hormone levels can affect your cycle or fertility. For example, teens tend to have low or changing progesterone levels. This is also true for women close to menopause. That is why teens and women in their 40s may have heavy menstrual bleeding and cycles that change in length.

Other things can change your cycle. They include birth control pills, low body fat, losing a lot of weight, or being overweight. Stress or very hard exercise also can change your cycle. Pregnancy is the most common cause of a missed period.

What common symptoms are linked to the menstrual cycle?

Some women have no pain or other problems. But other women have symptoms before and during their periods.

For about a week before a period, many women have some premenstrual symptoms. You may feel more tense or angry. You may gain water weight and feel bloated. Your breasts may feel tender. You may get acne. You also may have less energy than usual. A day or two before your period, you may start having pain (cramps) in your belly, back, or legs. These symptoms go away during the first days of a period.

When your ovary releases an egg in the middle of your cycle, you may have pain in your lower belly. You also might have red spotting for less than a day. Both are normal.

How can women take care of bleeding and symptoms?

You can use pads, tampons, or menstrual cups to manage bleeding. Be sure to change tampons at least every 4 to 8 hours. Pads or menstrual cups may be best at night.

Many women can improve their symptoms by getting regular exercise and eating a healthy diet. It also may help to limit alcohol and caffeine. Try to reduce stress.

A heating pad, hot water bottle, or warm bath also can help with cramps. You can take an over-the-counter medicine such as ibuprofen or naproxen before and during your period to reduce pain and bleeding.

Normal Menstrual Cycle

The menstrual cycle is the series of changes your body goes through to prepare for a possible pregnancy. About once a month, the uterus grows a new, thickened lining (endometrium) that can hold a fertilized egg. When there is no fertilized egg to start a pregnancy, the uterus then sheds its lining. This is the monthly menstrual bleeding (also called menstruation or menstrual period) that you have from your early teen years until your menstrual periods end around age 50 (menopause).

See a picture of a woman's reproductive system.

The menstrual cycle is measured from the first day of menstrual bleeding, Day 1, up to Day 1 of your next menstrual bleeding. Although 28 days is the average cycle length, it is normal to have a cycle that is shorter or longer.

• A teen's cycles may be long (up to 45 days), growing shorter over several years.
• Around ages 25 and 35, most women's cycles are regular, generally lasting 21 to 35 days.
• Around ages 40 to 42, cycles tend to be the shortest and most regular. This is followed by 8 to 10 years of longer, less predictable cycles until menopause.

Three phases of the menstrual cycle

The phases of your menstrual cycle are triggered by hormonal changes.

Menstrual period

On Day 1 of your cycle, the thickened lining (endometrium) of the uterus begins to shed. You know this as menstrual bleeding from the vagina. A normal menstrual period can last 4 to 6 days.

Most of your menstrual blood loss happens during the first 3 days. This is also when you might have cramping pain in your pelvis, legs, and back. Cramps can range from mild to severe. The cramping is your uterus contracting, helping the endometrium shed. In general, any premenstrual symptoms that you've felt before your period will go away during these first days of your cycle.

Follicular phase

During the follicular phase, an egg follicle on an ovary gets ready to release an egg. Usually, one egg is released each cycle. This process can be short or long and plays the biggest role in how long your cycle is. At the same time, the uterus starts growing a new endometrium to prepare for pregnancy.

The last 5 days of the follicular phase, plus ovulation day, are your fertile window. This is when you are most likely to become pregnant if you have sex without using birth control.

Luteal (premenstrual) phase

This phase starts on ovulation day, the day the egg is released from the egg follicle on the ovary. It can happen any time from Day 7 to Day 22 of a normal menstrual cycle. During ovulation, some women have less than a day of red spotting or lower pelvic pain or discomfort (mittelschmerz). These signs of ovulation are normal.

• If the egg is fertilized by sperm and then implants in (attaches to) the endometrium, a pregnancy begins. (This pregnancy is dated from Day 1 of this menstrual cycle.)
• If the egg is not fertilized or does not implant, the endometrium begins to break down.

After the teen years and before perimenopause in your 40s, your luteal phase is very predictable. It normally lasts 13 to 15 days, from ovulation until menstrual bleeding starts a new cycle. This 2-week period is also called the "premenstrual" period.

Many women have premenstrual symptoms during all or part of the luteal phase. You may feel tense, angry, or emotional. You may gain water weight and feel bloated. Or you may have tender breasts or acne. A day or more before your period, you may start to have pain (cramps) in your abdomen, back, or legs. It is normal to have less energy at this time. Some women also have headaches, diarrhea or constipation, nausea, dizziness, or fainting.

When premenstrual symptoms make your daily life difficult, you are said to have premenstrual syndrome (PMS). For more information, see the topic Premenstrual Syndrome (PMS).

Menarche and the Teenage Menstrual Cycle

Menarche (say "MEN-ar-kee") is a girl's first menstrual period. A first period usually happens after breasts, pubic hair, and underarm hair have begun to grow. Menarche is a sign of growing up and becoming a woman. It can happen as early as about age 9 or up to age 15. The first few periods are usually light and irregular. About 2 out of 3 girls have a regular pattern of menstrual periods within 2 years of menarche.^{footnote 1} During the teen years, periods may become longer and heavier. For more information, see Menarche.

Perimenopausal Menstrual Cycle

Perimenopause, which means "around menopause," refers to the 2 to 8 years of changing hormone levels and related symptoms that lead up to menopause. The most common sign of perimenopause is longer, often irregular menstrual cycles that are caused by hormonal ups and downs.

Most women start perimenopause between ages 39 and 51. Some women begin to notice menstrual changes and premenstrual syndrome (PMS) symptoms in their late 30s when hormones begin to fluctuate and fertility naturally declines. Other women don't notice perimenopausal changes until their late 40s.

Perimenopause is a time of unpredictability. Menstrual and hormone-related symptoms are different for every woman. Some notice few or no changes. And others have severe symptoms that disrupt their sleep and daily lives. As during the teen years, irregular cycles can lead to heavy menstrual bleeding. Other common symptoms include mild to severe hot flashes, insomnia, cloudy thinking, headaches, heart palpitations, mood swings, irritability, depression, and anxiety. Some of these symptoms can also be related to aging and other life changes. See your doctor to discuss your symptoms, whether you want symptom treatment, and which therapies you can consider.

See a doctor for menstrual bleeding that lasts longer than 7 days or for cycles that are shorter than 21 days or longer than 35 days. For more information, see the topics Abnormal Uterine Bleeding and Menopause and Perimenopause.

Managing Menstrual Cycle Symptoms and Bleeding

Keep a calendar and mark the day you start your menstrual period each month. If your cycle is regular, it can help you predict when you'll have your next period.

If you're trying to figure out whether you have a pattern of premenstrual symptoms, it may be helpful to keep a premenstrual daily symptom diary .

You can improve your body's ability to handle menstrual changes by getting regular exercise, eating a healthy diet, limiting alcohol and caffeine intake, and reducing stress. Non-prescription pain relievers can also help reduce some symptoms.

Medicine for menstrual pain and bleeding

Try a non-prescription medicine to help relieve your pain and bleeding. Start taking the recommended dose of pain reliever when symptoms begin or 1 day before your menstrual period starts. If you are trying to become pregnant, talk to your doctor before using any medicine. Be safe with medicines. Read and follow all instructions on the label.

• Non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (for example, Advil), reduce menstrual cramps, pain, and bleeding by lowering the level of the hormone prostaglandin.
• If NSAIDs do not relieve the pain, try acetaminophen, such as Tylenol.
• Take the medicine for as long as the symptoms would normally last if you did not take the medicine.

Be sure to follow all labels and directions. Do not take aspirin if you are younger than 18 because of the risk of Reye syndrome.

Additional ways to relieve menstrual cramps

• Apply heat to your abdomen with a heating pad or hot water bottle, or take a warm bath. Heat improves blood flow and may decrease pelvic pain.
• Lie down and elevate your legs by putting a pillow under your knees.
• Lie on your side and bring your knees up toward your chest. This will help relieve back pressure.
• Get regular exercise. This improves blood flow, produces pain-fighting endorphins, and may reduce pain.
• If you have vaginal pain with cramps, try using pads instead of tampons.

For more information on managing menstrual cramps, see:

• Menstrual Cycle: Dealing With Cramps.

Managing menstrual bleeding

You can choose from a range of pads, tampons, or menstrual cups to manage menstrual bleeding. Follow all directions included with the product of your choice.

• Pads range from thin and light to thick and superabsorbent. They protect your clothing, with or without using a tampon. Pads may be your best choice for use at night.
• Tampons range from small to large, for light to heavy flow. You can place a tampon in the vagina by using a slender tube (that is packaged with the tampon) or by tucking it in with a finger. Be sure to change a tampon at least every 4 to 8 hours. This helps prevent leakage and infection.
• Menstrual cups are inserted in the vagina to collect menstrual flow. You remove the menstrual cup to empty it. Some are disposable and some can be washed and used again.

Whatever you use, be sure to change it regularly. Tampons and menstrual cups are ideal for activities that pads aren't practical for, such as swimming. Tampons should be changed at least every 4 to 8 hours, so they may not work as well for nighttime use. Menstrual cups can be worn for up to 12 hours. It may take some experimenting to find the right products for you.

When to Call a Doctor

There is a broad range of "normal" among menstruating women. Unpredictable or long menstrual cycles are normal for teenagers and women in their 40s. For teens, a normal cycle can be as short as 21 days or as long as 45 days^{footnote 2}. If you are a teen, you can expect cycles to even out over time. If you are nearing the age of menopause, you can expect menstrual cycles to become longer and eventually to stop. If you are not a teen and you are not older than 40 and your cycles are shorter than 21 days or longer than 35 days, there is a chance that you have a problem that needs to be checked by your doctor.

You will need a medical check by a doctor if you have any change in your menstrual pattern or amount of bleeding that affects your daily life. This includes menstrual bleeding, for three or more menstrual cycles, that:

• Lasts longer than 7 days.
• Is a sudden or big change from your usual period.
• Is very heavy. This means that you are passing large clots or soaking through your usual pads or tampons each hour for 2 or more hours.

Other symptoms you need to have checked include:

• Bleeding between menstrual periods.
• Pelvic pain that is not linked to menstrual bleeding and lasts longer than a day.

If you are a teenage girl, see your doctor if you have not started having periods by age 15.

For more information, see the topics Abnormal Vaginal Bleeding and Abnormal Uterine Bleeding.