What is menstruation?

Menstruation (pronounced men-stroo-EY-shuhn) is normal discharge of blood and tissue from the uterine lining through the vagina (see diagram) that occurs as part of a woman's monthly menstrual cycle. Menstruation occurs between menarche (pronounced muh-NAHR-kee), a girl's first period, and menopause, when menstrual cycles end. The average menstruation time in normally menstruating women is about 5 days. In the United States, most girls start menstruating shortly after 12 years of age.

What is the menstrual cycle?

The menstrual cycle is the monthly process in which female hormones stimulate an ovary to release an egg, thicken the lining of the uterus to support a pregnancy, and then cause the uterus to shed this lining (through menstruation) if there is no pregnancy. The average menstrual cycle is 28 days, but this varies between women and from month to month. In teens, the menstrual cycle can range from 21 to 45 days, but for most women, it is 21 to 35 days.

Day 1

The first day of bleeding is considered the first day of the menstrual cycle. After bleeding ends, usually around day 5, levels of the hormone estrogen begin to rise. The rise in estrogen causes the lining of the uterus to thicken as it prepares to hold a fertilized egg. At the same time, the changes in hormone levels cause follicles (the sacs in the ovary that contain eggs) to grow and mature, in preparation for one follicle to go through ovulation.

Ovulation

Around day 12 to 14 in an average 28-day cycle, the egg is released from a follicle on the ovary in a process called ovulation (pronounced ov-yu-LAY-shuhn). Ovulation can occur anywhere between 10 and 21 days after the first day of a woman's menstrual cycle. A woman can tell when she has begun ovulating using several methods, including at-home tests that measure levels of luteinizing hormone (LH) in the urine and keeping track of her body temperature, which typically rises slightly at ovulation. At mid-cycle, some women experience pain on one side of their pelvic area; this pain is called "Mittelschmerz" (meaning "middle pain," because it occurs in the middle of the cycle) and may be a signal of ovulation.

If a pregnancy does not occur, decreasing hormone levels signal for the lining of the uterus, called the endometrium, to be shed during menstruation.

The endometrium builds up and breaks down during the menstrual cycle. The endometrium is thickest halfway through the 28-day cycle. Then, if there is no pregnancy, it breaks down. This breakdown causes the bleeding of the menstrual phase. This diagram illustrates an average 28-day cycle.

What happens if a pregnancy occurs?

Fertilization

After ovulation, the egg moves down the fallopian tube. The sperm can fertilize the egg at this point. After the sperm is ejaculated into the vagina, it moves into the cervix and through the uterus into the fallopian tube. Sperm can live up to 5 days in a woman's body.
If fertilization occurs, the newly formed embryo travels through the fallopian tube into the uterus, where it implants in the wall of the uterus. If fertilization does not occur, the egg naturally breaks down, and the uterine wall is lost in the form of menstrual bleeding.

Implantation

The embryo must successfully implant into the thickened wall of the uterus for the pregnancy to occur. The embryo first attaches to the wall of the uterus around 5 or 6 days after ovulation. It becomes more firmly implanted between 6 and 12 days after ovulation. Implantation causes a release of hCG—a hormone that signals the body to change to support the pregnancy. This hormone is what a pregnancy test detects.

For most women, a normal menstrual cycle ranges from 21 to 35 days. However, 14% to 25% of women have irregular menstrual cycles, meaning the cycles are shorter or longer than normal; are heavier or lighter than normal; or are experienced with other problems, like abdominal cramps. Irregular cycles can be ovulatory, meaning that ovulation occurs, or anovulatory, meaning ovulation does not occur.

The most common menstrual irregularities include:

• Amenorrhea (pronounced ey-men-uh-REE-uh) or absent menstrual periods: When a woman does not get her period by age 16, or when she stops getting her period for at least 3 months and is not pregnant.
• Oligomenorrhea (pronounced ol-i-goh-men-uh-REE-uh) or infrequent menstrual periods: Periods that occur more than 35 days apart.
• Menorrhagia (pronounced men-uh-REY-jee-uh) or heavy menstrual periods: Also called excessive bleeding. Although anovulatory bleeding and menorrhagia are sometimes grouped together, they do not have the same cause and require different diagnostic testing.
• Prolonged menstrual bleeding: Bleeding that exceeds 8 days in duration on a regular basis.
• Dysmenorrhea (pronounced dis-men-uh-REE-uh): Painful periods that may include severe menstrual cramps.

Additional menstrual irregularities include:

• Polymenorrhea (pronounced pol-ee-men-uh-REE-uh): Frequent menstrual periods occurring less than 21 days apart
• Irregular menstrual periods with a cycle-to-cycle variation of more than 20 days
• Shortened menstrual bleeding of less than 2 days in duration
• Intermenstrual bleeding: Episodes of bleeding that occur between periods, also known as spotting

Pain that you get with your menstrual period is called dysmenorrhea (dis-men-uh-REE-uh). Pain is the most common problem women have with their periods. More than half of women who have periods get some pain around their period. Some women may get just a feeling of heaviness in the abdomen or tugging in the pelvic area. Other women experience severe cramps different from premenstrual syndrome (PMS) pain.

A majority of period pain can be relieved by over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs) such as naproxen, ibuprofen, or aspirin. Starting an over-the-counter NSAID medicine when your period first starts may also lessen heavy menstrual bleeding and help control the pain better.

There are two types of dysmenorrhea:

• Primary dysmenorrhea. This is the most common type of dysmenorrhea. The pain is usually caused by contractions of the uterus (womb). The uterus contracts during your period to help the uterine lining leave the body. Teens may get dysmenorrhea soon after they get their first period. For most women, primary dysmenorrhea gets less painful as they get older. But some women get severe menstrual pain. Your risk for dysmenorrhea may be higher if you:
  • Got your first period before age 11
  • Have longer or heavier periods
  • Smoke
  • Have high levels of stress

• Secondary dysmenorrhea. This type of dysmenorrhea is usually caused by another health problem. Pain from secondary dysmenorrhea usually gets worse as you get older. It also lasts longer than normal menstrual cramps. Problems that cause secondary dysmenorrhea include:
  • Endometriosis. This condition happens when the lining of the uterus grows outside of the uterus where it does not belong. In response to monthly changes in levels of the hormone estrogen, this lining breaks down and bleeds outside of the uterus and can cause swelling and pain.
  • Uterine fibroids. Fibroids are tumors that grow in or on the wall of the uterus. They are almost always not cancerous. Some women with fibroids experience pelvic pain and vaginal bleeding at times when they do not have their period.
  • Ovarian cysts. Cysts are fluid-filled sacs on the ovary. Ovarian cysts usually don’t cause any symptoms, but some can cause pain during your period or at ovulation.

When to see your doctor

Talk to your doctor or nurse if over-the-counter pain medicine, such as ibuprofen or naproxen, does not help or if the pain interferes with daily activities like work or school. Your doctor or nurse will ask you questions and do some tests, including possibly a physical exam, to rule out any other health problem. Keeping track of your symptoms and periods in a diary or calendar can help your doctor or nurse diagnose any health problems.

See your doctor to rule out other health problems if:

• You have blood clots in your menstrual flow that are larger than a quarter.
• Your pain happens at times other than just before your period or during your period.

Treatment depends on what is causing your pain. Your doctor may prescribe hormonal birth control, such as a hormonal intrauterine device (IUD), the pill, shot, or vaginal ring, to help with pain from endometriosis, fibroids, or ovarian cysts. Hormonal birth control is sometimes prescribed by doctors for women’s health concerns other than preventing pregnancy. You may also need surgery, as a last resort, if one of these conditions is causing your pain.

Your periods are considered irregular if your menstrual cycle is shorter or longer than average. This means that the time from the first day of your last period up to the start of your next period is less than 24 days or more than 38 days.

Your periods can also be irregular if your cycle length varies by more than 20 days from month to month. An example would be your cycle jumping from a normal 25-day cycle to a 46-day cycle the next month and then back to a 25-day cycle the following month.

Irregular periods are normal for teenage girls and perimenopausal women. Teen girls’ periods may be irregular for the first few years before becoming more regular. During the transition to menopause, called perimenopause, menstrual cycles may become more irregular over time.

Causes of irregular periods include:

• Eating disorders. Irregular or missed periods can be signs of eating disorders, most often anorexia nervosa. But any eating disorder, including bulimia nervosa and binge eating disorder, can cause irregular periods.
• Thyroid problems, such as hyperthyroidism (hy-pur-THY-roi-diz-uhm). Hyperthyroidism, or overactive thyroid, causes your thyroid to make more thyroid hormone than your body needs. Hyperthyroidism can also cause fewer and lighter menstrual periods than normal.
• High amounts of prolactin in the blood. This condition is called hyperprolactinemia (hy-pur-pro-LAK-te-nee-me-uh). Prolactin is the hormone that causes breasts to grow during puberty and makes breastmilk after childbirth. It also helps control the menstrual cycle.
• Certain medicines, such as those for epilepsy or anxiety
• Polycystic ovary syndrome (PCOS), a condition that usually causes multiple ovarian cysts, hormonal imbalance, and irregular periods. About 1 in 10 women with irregular menstrual cycles has PCOS.
• Primary ovarian insufficiency (POI). POI happens when your ovaries stop working normally before age 40. It can happen as early as the teenage years. POI is not the same as premature menopause. Unlike women who go through premature menopause, women with POI may still have periods, though they are most often irregular. Women with POI may also still get pregnant.
• Pelvic inflammatory disease (PID). Irregular periods can be a sign of PID, an infection of the reproductive organs. PID is most often caused by a sexually transmitted infection (STI).
• Stress. Studies show high levels of chronic (long-term) stress can lead to irregular periods.
• Uncontrolled diabetes. Type 1 and type 2 diabetes can cause irregular periods, but getting your diabetes under control can help your periods become more regular.
• Obesity. The extra fat in the body makes the hormone estrogen. The extra estrogen changes the normal menstrual cycle and can cause missed, irregular, or heavy periods.

When to call the doctor

• You get irregular periods after having normal cycles.
• Your period happens more often than every 24 days or less often than every 38 days.

Treatment depends on the cause of the irregular periods. Your doctor may give you hormonal birth control, such as a hormonal IUD, the pill, shot, or vaginal ring, to help control your menstrual cycle. Hormonal birth control is sometimes prescribed by doctors for women’s health concerns other than preventing pregnancy.

Heavy periods affect one in five American women each year. If you have heavy bleeding, your periods may be so painful and heavy that you find it hard to do normal activities such as going to work or school.

Causes of heavy bleeding include:

• Problems with ovulation. In a normal menstrual cycle, your uterine lining builds up and thickens to prepare for pregnancy. If pregnancy does not happen, the uterine lining leaves your body during your period. If your hormones get out of balance or if you do not ovulate, the uterine lining can build up too much and bleed heavily and in an unpredictable pattern.
• Problems with the uterine lining. If your hormones or uterine lining get out of balance, the uterine lining can bleed too much. This can cause heavy bleeding as the lining is pushed out during the next menstrual period.
• Thyroid problems. Heavy bleeding can be a sign of hypothyroidism (hy-poh-THY-roi-diz-uhm), or underactive thyroid. Hypothyroidism happens when your thyroid does not make enough thyroid hormones.
• Uterine fibroids. Fibroids are made of muscle tissue that grows in or on the wall of the uterus. They are almost always not cancer. They can cause pain and heavy or irregular bleeding.
• Uterine polyps. Polyps are an overgrowth of the endometrial tissue that lines the inside of the uterine wall. They are usually small. They are usually not cancer but can cause heavy or long periods.
• Certain medicines. Some medicines, such as blood thinners, can cause heavy or long periods.
• Pregnancy problems. Unusual or not regular heavy bleeding can be caused by a miscarriage (an early pregnancy that ends) or an ectopic pregnancy. An ectopic pregnancy is when the fertilized egg implants outside of the uterus (womb) where it does not belong, putting a woman’s life in danger. Ectopic pregnancies can never end in a healthy pregnancy and are a medical emergency.
• Bleeding disorders. Hemophilia and von Willebrand’s disease are inherited bleeding disorders that cause heavy bleeding during periods. Studies show that up to one in five white women with heavy periods has a bleeding disorder. Bleeding disorders are less common in African-American women, affecting about one in 20 African-American women with heavy bleeding. For many women, heavy menstrual bleeding is the only sign they have a bleeding disorder.
• Obesity. The extra fat in the body makes the hormone estrogen. The extra estrogen changes the normal menstrual cycle and can cause missed, irregular, or heavy periods.

Some research has found that women with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) have a higher risk for heavy bleeding. Women with ME/CFS may experience a range of symptoms that can include fatigue (tiredness or exhaustion that does not get better with rest and sleep), muscle and joint pain, and memory problems.

When to call the doctor

• Your period lasts longer than eight days.
• You bleed through one or more pads or tampons every one to two hours.
• You feel dizzy, lightheaded, weak, or tired, or if you have chest pain or trouble breathing during or after your period. These can be symptoms of anemia. Anemia is a condition that happens when your blood cannot carry enough oxygen to your body because of a lack of iron.
• You pass menstrual blood clots larger than the size of quarters. (It is normal to pass clots the size of quarters or smaller.)

Your doctor or nurse may try treating heavy bleeding first with hormonal birth control, such as a hormonal IUD, the pill, shot, or vaginal ring. Hormonal birth control is sometimes prescribed by doctors for women’s health concerns other than preventing pregnancy. Your doctor may also suggest trying over-the-counter pain relievers, such as naproxen or ibuprofen, which may lessen bleeding for some women, especially when taken immediately before your period starts or as soon as your period starts.

If birth control or other medicines do not help, you may need surgery to treat the cause of heavy bleeding. Surgery for heavy bleeding is usually the last treatment option women and their doctors consider because surgery always has risks.

Unusual or abnormal bleeding is any bleeding that is different from your typical menstrual period or happens when you do not have your period.

Causes of unusual bleeding include:

• Hormonal changes. Changing hormone levels during puberty and perimenopause, the transition to menopause, can cause longer, heavier periods. They can also cause irregular cycles.
• Endometriosis. This condition happens when the lining of the uterus grows outside of the uterus where it does not belong.
• Ovarian cysts. Unusual bleeding may be a sign of an ovarian cyst that has ruptured (burst).
• Cancer, such as uterine, cervical, and ovarian cancer. Any vaginal bleeding after menopause can be a sign of a serious health problem, including ovarian, cervical or uterine cancer.

When to see the doctor

You should see your doctor if you have unusual bleeding. This may include:

• Bleeding after sex, more than once
• Spotting or bleeding anytime in the menstrual cycle other than during your period
• Bleeding during your period that is heavier or lasts longer than normal
• Bleeding after menopause

Your doctor may start by checking for problems that are most common in your age group. Some of these are not serious and are easy to treat. Your doctor may prescribe hormonal birth control, such as a hormonal IUD, the pill, shot, or vaginal ring, to help control your menstrual cycle. Hormonal birth control is sometimes prescribed by doctors for women’s health concerns other than preventing pregnancy. Other types of bleeding, such as any vaginal bleeding after menopause, can be more serious.

The absence of menstrual periods before menopause is called amenorrhea (ay-men-uh-REE-uh). You may have amenorrhea if you:

• Haven’t had a period for three months in a row
• Haven’t had your first period by age 15

Amenorrhea happens in 3% to 4% of women.

Amenorrhea that is not caused by pregnancy or breastfeeding could mean that your ovaries stopped making normal amounts of the hormone estrogen. Missing this hormone can have serious effects on your health.

Causes of amenorrhea include:

• Pregnancy. Your period stops during pregnancy because your ovaries no longer release eggs. You may get some spotting (light vaginal bleeding), but this is common and usually does not mean a problem with the pregnancy. If you have spotting during pregnancy you should see your doctor or nurse to be sure. Learn more in our Pregnancy section.
• Breastfeeding. For some women, their periods do not come back until after breastfeeding ends. For others, their periods may return within a few months of giving birth. While your baby transitions from breastfeeding to other foods you may ovulate and not realize it. All women should talk to their doctor or nurse about birth control methods during breastfeeding if they do not want to get pregnant again right away. Learn more in our Breastfeeding section.
• Eating disorders, especially anorexia nervosa. Amenorrhea can happen if your body fat drops so low that ovulation stops. Anorexia often causes extreme weight loss leading to a very low body weight that is not healthy. This can cause periods to be less regular or stop completely.
• Weight. Gaining too much weight or losing too much weight can cause missed periods. Menstrual periods will usually restart after losing weight if you are overweight or gaining weight if you are underweight.
• Stress. Long-term, severe stress can affect the part of your brain that controls reproduction. As a result, ovulation and your period can stop. Managing the stress can help restore normal menstrual cycles.
• Hormonal problems. This includes problems with the reproductive organs or those caused by health conditions such as polycystic ovary syndrome (PCOS).
• Other serious health problems, including birth defects and tumors in the brain. Once these problems are treated, your period may start for the first time or you may get your period again if it had stopped.

When to call the doctor

• You have gone three months without a period and are not pregnant or breastfeeding.
• You have not gotten your period by age 15.
• You have not started your period within three years after breast growth began, or if breasts haven’t started to grow by age 13.

About four in 10 women will get a migraine (a painful, severe headache) in their lifetime. About half of those women report that their migraine happens around their periods.

Researchers are not sure what causes migraine. Many factors can trigger migraine, including stress, anxiety, and bright or flashing lights. Also, hormones that control the menstrual cycle may affect headache-related chemicals in the brain.

When to see the doctor

See your doctor if you think you have migraine headaches. If you already know you have migraine, you should schedule an appointment if:

• Your headaches change.
• Treatments that once worked no longer help.
• You have side effects from your medicine.
• You take hormonal birth control pills and have migraine with aura (seeing bright flashing lights or spots that aren’t real).
• Your headaches are worse when you lie down.

Migraine cannot be cured, but your doctor can help you manage them. A key step is identifying what triggers a migraine and planning how to avoid these triggers.

Your doctor may prescribe medicine to reduce the number of migraines. Medicines may include antidepressants, blood pressure medicines, certain types of hormonal birth control, and seizure medicines. Botox injections may also help prevent migraine.

Other medicines can help when a migraine starts. These include over-the-counter pain medicines and prescription medicines. Learn more on our Migraine page.

Menstrual irregularities occur in an estimated 14% to 25% of women of childbearing age.

Estimates of the number of women with menstrual irregularities may differ by the cause or nature of the irregularity. For example, if a woman experiences severe cramps, she might be included in the tally of women with endometriosis rather than in the tally of women with menstrual irregularities.

Menstrual irregularities can have a variety of causes, including pregnancy, hormonal imbalances, infections, diseases, trauma, and certain medications.

Causes of irregular periods (generally light) include:

• Perimenopause (generally in the late 40s and early 50s)
• Primary ovarian insufficiency (POI)
• Eating disorders (anorexia nervosa or bulimia)
• Excessive exercise
• Thyroid dysfunction (too much or too little thyroid hormone)
• Elevated levels of the hormone prolactin, which is made by the pituitary gland to help the body produce milk
• Uncontrolled diabetes
• Cushing's syndrome (elevated levels of the hormone cortisol, used in the body's response to stress)
• Late-onset congenital adrenal hyperplasia (problem with the adrenal gland)
• Hormonal birth control (birth control pills, injections, or implants)
• Hormone-containing intrauterine devices (IUDs)
• Scarring within the uterine cavity (Asherman's syndrome)
• Medications, such as those to treat epilepsy or mental health problems

Common causes of heavy or prolonged menstrual bleeding include:

• Adolescence (during which cycles may not be associated with ovulation)
• Polycystic ovary syndrome (PCOS) (bleeding irregular but heavy)
• Uterine fibroids (benign growths of uterine muscle)
• Endometrial polyps (benign overgrowth of the lining of the uterus)
• Adenomyosis (the presence of uterine lining in the wall of the uterus)
• Nonhormonal IUDs
• Bleeding disorders, such as leukemia, platelet disorders, clotting factor deficiencies, or (less common) von Willebrand disease
• Pregnancy complications (miscarriage)

Common causes of dysmenorrhea (menstrual pain) include:

• Endometriosis (uterine lining grows outside the uterus)
• Uterine abnormalities (fibroids or adenomyosis)
• IUDs
• Pelvic scarring due to sexually transmitted infections, such as chlamydia or gonorrhea
• Heavy menstrual flow

A health care provider diagnoses menstrual irregularities using a combination of the following:

• Medical history
• Physical examination
• Blood tests
• Ultrasound examination
• Endometrial biopsy—a small sample of the uterus's endometrial lining is taken to be examined under a microscope
• Hysteroscopy—a diagnostic scope that allows a health care provider to examine the inside of the uterus, typically done as an outpatient procedure
• Saline infusion sonohysterography—ultrasound imaging of the uterine cavity while it is filled with sterile saline solution
• Transvaginal ultrasonography—ultrasound imaging of the pelvic organs, including the ovaries and uterus, using an ultrasound transducer that is inserted into the vagina

Treatments for menstrual irregularities often vary based on the type of irregularity and certain lifestyle factors, such as whether a woman is planning to get pregnant.

Treatment for menstrual irregularities that are due to anovulatory bleeding (absent periods, infrequent periods, and irregular periods) include:

• Oral contraceptives
• Cyclic progestin
• Treatments for an underlying disorder that is causing the menstrual problem, such as counseling and nutritional therapy for an eating disorder

Treatment for menstrual irregularities that are due to ovulatory bleeding (heavy or prolonged menstrual bleeding) include:

• Insertion of a hormone-releasing intrauterine device
• Use of various medications (such as those containing progestin or tranexamic acid) or nonsteroidal anti-inflammatory medications

If the cause is structural or if medical management is ineffective, then the following may be considered:

• Surgical removal of polyps or uterine fibroids
• Uterine artery embolization, a procedure to block blood flow to the uterus
• Endometrial ablation, a procedure to cauterize (remove or close off by burning) blood vessels in the endometrial lining of the uterus
• Hysterectomy

Treatment for dysmenorrhea (painful periods) include:

• Applying a heating pad to the abdomen
• Taking nonsteroidal anti-inflammatory medications
• Taking contraceptives, including injectable hormone therapy or birth control pills, using varied or less common treatment regimens

Menstrual irregularities can be caused by many different underlying causes. Some of these causes can make it harder to get pregnant, including:

• Polycystic ovary syndrome (PCOS)
• Endometriosis
• Primary ovarian insufficiency (POI)
• Uterine fibroids

Menstrual irregularities are often a sign of an underlying condition and, in some cases, the underlying condition may be associated with a higher risk for cancer. For example, absent and irregular periods associated with estrogen production but no progesterone production are associated with endometrial cancer in about 14% of women, if the problem is recurrent. Women who experience irregular periods on a frequent basis may also have a higher risk of ovarian cancer after age 70. Menstrual irregularities such as heavy or prolonged menstrual bleeding are not known to be associated with cancer.

The presence of menstrual irregularities can be a sign of other health problems such as thyroid disease, POI, endometriosis, PCOS, polyps, and uterine fibroids. If left untreated, menstrual irregularities can lead to or contribute to other conditions. These possible conditions vary depending on the type of menstrual irregularity, but some include thickening of the lining of the uterus (called endometrial hyperplasia), low bone density, and iron-deficient anemia.

It is important for a woman with a menstrual irregularity to speak to a health care provider to determine the cause of the irregularity and to receive appropriate treatment as necessary.

Use a calendar to keep track of your menstrual cycle. You can mark each day of your period with an "X." Calculate the length of your cycle by counting the days from the first day of bleeding in one period to the first day of bleeding in the next period. In addition to noting the days of your period, it is helpful to make notes about the flow, any pain that is felt, and changes in mood or behavior. Many apps now exist to make tracking your cycle even easier using a smartphone.

It is important to contact your health care provider promptly about any significant changes in your menstrual cycle. It is also important to contact your provider if your cycles are associated with significant bleeding or pain, even if your cycle has always been that way. The presence of menstrual irregularities can be indicative of other health problems, such as POI, endometriosis, PCOS, polyps, or uterine fibroids. Your health care provider can order the appropriate tests to diagnose the cause of the menstrual irregularity and provide appropriate treatment.