Menstruation is the monthly bleeding that happens during a woman's menstrual cycle.

The menstrual cycle is the series of hormonal changes that a female’s body goes through in preparation for pregnancy.

Each month, the lining of the uterus (or womb) thickens. The body sheds this lining, along with blood, if no fertilized egg attaches to the wall of the uterus. The blood and tissue pass out of the body through the vagina.

The menstrual period, or menstruation, typically lasts three to five days for most women.

Every woman's menstrual cycle is slightly different. A normal menstrual cycle length can be anywhere from 21 to 35 days. The average length of a menstrual cycle is 28 days.

How Hormones Play a Role

At the beginning of the menstrual cycle, rising levels of estrogen, which along with another hormone called FSH (follicle stimulating hormone), help produce a mature egg and ready the body for pregnancy. Once the egg is released from the ovaries to the uterus during ovulation, levels of progesterone rise in preparation of pregnancy. If pregnancy does not occur, both estrogen and progesterone drop, which results in menstruation.

Phases of the Menstrual Cycle

There are four phases of the menstrual cycle, including menses, follicular, ovulation, and luteal.

Menses The first stage of the menstrual cycles is menses, which begins on the day you get your period. During this phase, the endometrium, or the lining of the uterus, which thickens each month in preparation for a fertilized egg, is shed through the vagina if pregnancy hasn’t occurred. Menstruation typically occurs for three to five days, though some women may bleed for only three days while others may bleed longer than five.

Follicular This phase starts on the first day of menstruation so there is some overlap with the menses phase. It is the longest phase of the menstrual cycle, lasting about two weeks until ovulation. During the follicular phase, hormones released by the ovaries cause the endometrium to thicken and follicles in the ovaries to grow. During the latter part of the follicular phase, one of these follicles will form a fully mature egg.

Ovulation In a 28-day cycle, ovulation occurs at about day 14. There will be some variation in when ovulation occurs depending on whether your menstrual cycle is shorter or longer than average. During this phase, the ovary releases its egg.

Luteal During the luteal phase, which typically lasts from day 15 to 28, the egg moves through the fallopian tube to the uterus. If it becomes fertilized with sperm and attaches to the uterine wall, pregnancy occurs. If this doesn’t happen, you’ll get your period and the cycle begins again.

Menstrual Cramps (Dysmenorrhea)

Dysmenorrhea, or menstrual cramping, is pain associated with menstruation.

Menstrual cramps are common. A study published in June 2019 in the American Journal of Obstetrics and Gynecology involving nearly 43,000 women and girls found 85 percent of participants reported pain with their period.

Hormones called prostaglandins can cause menstrual cramping. Prostaglandins are produced by the lining of the uterus.

Cramps usually occur right before menstruation starts and may last for a day or two. Over-the-counter pain relievers like ibuprofen, can help relieve menstrual cramps. Some women find applying heat with a heating pad or hot water bottle or taking a warm bath helps. Pain typically decreases throughout the period as you shed the uterine lining.

See your doctor if pain gets worse as menstruation continues, doesn't go away after the end of the period, or is so severe that you’re not able to complete daily tasks. These may be signs of a more serious medical problem, including endometriosis or uterine fibroids.

Irregular Periods

Certain menstrual cycle disorders can cause a woman's period to be irregular, absent, or infrequent.

Periods are considered irregular if they are shorter or longer than average, meaning the time between the start of menstruation periods is less than 24 days or more than 38 days.

Irregular periods tend to occur in adolescent girls and may last for a few years until they become regular. Perimenopausal women may also experience irregular periods as they transition to menopause.

Some women experience absent or infrequent periods.

Amenorrhea Amenorrhea refers to the absence of periods for three to six months in a woman who has previously had periods or when menstrual periods haven't started by age 15.

Oligomenorrhea This is a medical term for infrequent periods. Women with oligomenorrhea have fewer than six to eight periods in a year.

Certain conditions can lead to irregular periods, including:

Eating disorders
Stress
Thyroid problems
Uncontrolled diabetes
Obesity
Polycystic ovary syndrome (PCOS)
Endometriosis
Hyperprolactinemia, or high amounts of the hormone prolactin in the blood
Primary ovarian insufficiency
Pelvic inflammatory disease

Some medications, including those that treat epilepsy and anxiety can also cause irregular periods.

See your doctor if you miss more than three menstrual periods in a row, or three menstrual periods over the course of a year.

Treating underlying conditions can help periods become more regular. Your doctor may suggest medication, such as hormonal birth control, to help regulate your period. Surgery may be needed to treat conditions like endometriosis. If stress is the culprit, stress reduction and relaxation techniques like meditation can help.

Heavy Periods

Menorrhagia is the medical term for menstrual bleeding that lasts longer than normal or is very heavy.

Heavy periods are quite common, affecting about one-third of women, according to the American College of Obstetricians and Gynecologists (ACOG).

They can also be a sign of other health problems, including:

Fibroids and polyps (growths in and around the uterus that can affect blood flow)
Adenomyosis, which occurs when endometrial tissue grows into the wall of the uterus, and endometriosis, which occurs when that tissue grows outside the uterus
Bleeding disorders
Irregular ovulation, which can occur with PCOS and hypothyroidism
Endometrial cancer

Certain medications, like blood thinners and copper intrauterine devices, can also cause heavy periods.

Heavy menstrual bleeding can lead to anemia (low red blood cell count, or lack of hemoglobin in the blood), which can increase the risk of heart problems.

Talk to your doctor if:

Your periods last longer than seven days
Your menstrual flow soaks through one or more tampons (or pads) every hour for several hours in a row
Your periods contain blood clots the size of a quarter or larger
You're unusually tired or short of breath during your period

Medications are often the first line of treatment for heavy periods. These include hormonal birth control pills, nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, and tranexamic acid (Lysteda), a prescription drug taken once a month at the start of your period to treat heavy bleeding.

Surgery to treat adenomyosis, endometriosis, or fibroids can also help resolve heavy menstrual bleeding.

Common Questions & Answers

What happens during menstruation?

Menstruation is when your body sheds the thickened lining of your uterus (called the endometrium) each month that pregnancy has not occurred. The blood and tissue pass out of the body through the vagina.

How many days is menstruation?

Menstruation typically lasts three to five days for most women, though some women may bleed for just three days while others may bleed for longer than five days.

What are the four phases of the menstrual cycle?

The four phases of the menstrual cycle include menses, the follicular phase, ovulation, and the luteal phase.

At what age does menstruation usually begin?

Most girls get their first period between the ages of 12 and 13, but some may begin menstruating when they’re younger or older. Typically, your period begins two to three years after your breasts start to develop.

When do you stop getting your period?

Women’s periods begin to stop when they transition into menopause (known as perimenopause). This typically occurs between the ages of 45 and 55 though it can happen earlier. Menopause is diagnosed when a woman has gone 12 months without having a menstrual period.

Premenstrual Syndrome (PMS)

PMS is a combination of physical and mental symptoms — including bloating, breast tenderness, headaches, irritability, moodiness, and fatigue — that women experience about a week or two before their period.

About 90 percent of women report having symptoms of PMS, according to the U.S. Department of Health and Human Services Office on Women’s Health.

Some experience mild symptoms, while others may need to miss school or work because symptoms can be severe.

Over-the-counter pain relievers, such as ibuprofen, can help alleviate some PMS symptoms. If they don’t work, prescription medications, including hormonal birth control or antidepressants may be an option. Lifestyle changes can also ease symptoms of PMS, including regular exercise, sufficient sleep, and a healthy diet.

Limiting caffeine, alcohol, salt, and sugar in your diet can also help.

Period Tracking

If you're trying to get pregnant, keeping a record of your period can help you figure out when you're ovulating and whether your period is late.

Tracking periods can also help you spot any irregularities or changes to your menstrual cycle. Experts recommend marking each day of your period with an "X" on a calendar. Note any pain or changes in flow.

There are many websites and apps that offer free period trackers or period calculators. Be aware, though, that many period-tracking apps have been found to be inaccurate, according to a review published in the journal Obstetrics and Gynecology.

But if you’re interested in trying period trackers, consider the following:

Flo

One of the most popular period tracking apps, Flo allows you to log dozens of symptoms and activities, from sleep to how much water you’re drinking to discharge color, and more. Taken together, these logs can help predict when your period (and ovulation) should come next.

Spot On From Planned Parenthood

The app is a birth control, period, and fertility tracker that can help you keep tabs on spotting, flow intensity, and other cycle nuances, as well as track various birth control methods, including the pill, patch, ring, shot, IUD, and implant. You’ll receive regular birth control reminders and notifications and you’ll be able to log how you’re feeling throughout your cycle.

OvaGraph

Available as an app or on the web, OvaGraph is a good option if you’re trying to conceive. The program allows you to track all your natural signs of fertility, including basal body temperature, vaginal sensations, menstrual cycle timing, cervical mucus, cervical position, and more. All of this information together gives you the greatest odds of correctly predicting your date of ovulation.

Natural Cycles

Cleared by the U.S. Food and Drug Administration (FDA) as a form of contraception in 2018, Natural Cycles is a digital birth control method that predicts fertility status with your basal body temperature.

Each morning, you take your temperature when you wake up, and the app indicates whether your body temperature makes you likely to conceive (indicated in red) or not (green). According to its website, the company claims the app is 93 percent effective as a birth control option with typical use.

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Period Problems. Office on Women’s Health. February 22, 2021.
Irregular Periods. Cleveland Clinic. January 18, 2023.
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