Onset and frequency

The first menstrual period occurs after the onset of pubertal growth, and is called menarche. The average age of menarche is 12 to 15.^[1][9] However, it may start as early as eight.^[2] The average age of the first period is generally later in the developing world, and earlier in the developed world.^[5] The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women and 21 to 31 days in adults (an average of 28 days).^[2][5] The average age of menarche has changed little in the United States since the 1950s.^[5]

Menstruation is the most visible phase of the menstrual cycle and its beginning is used as the marker between cycles. The first day of menstrual bleeding is the date used for the last menstrual period (LMP). The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 31 days in adults (an average of 28 days).^[2][5]

Perimenopause is when fertility in a female declines, and menstruation occurs less regularly in the years leading up to the final menstrual period, when a female stops menstruating completely and is no longer fertile. The medical definition of menopause is one year without a period and typically occurs between 45 and 55 in Western countries.^{[6][10]:p. 381}

During pregnancy and for some time after childbirth, menstruation does not occur; this state is known as amenorrhoea. If menstruation has not resumed, fertility is low during lactation. The average length of postpartum amenorrhoea is longer when certain breastfeeding practices are followed; this may be done intentionally as birth control.

Health effects

Cramps

Painful menstrual cramps that result from an excess of prostaglandin release are referred to as primary dysmenorrhea. Primary dysmenorrhea usually begins within a year or two of menarche, typically with the onset of ovulatory cycles.^[13] Treatments that target the mechanism of pain include non-steroidal anti-inflammatory drugs (NSAIDs) and hormonal contraceptives. NSAIDs inhibit prostaglandin production. With long-term treatment, hormonal birth control reduces the amount of uterine fluid/tissue expelled from the uterus. Thus resulting in shorter, less painful menstruation.^[14] These drugs are typically more effective than treatments that do not target the source of the pain (e.g. acetaminophen).^[15] Risk factors for primary dysmenorrhea include: early age at menarche, long or heavy menstrual periods, smoking, and a family history of dysmenorrhea.^[13] Regular physical activity may limit the severity of uterine cramps.^[13]

For many women, primary dysmenorrhea gradually subsides in late second generation. Pregnancy has also been demonstrated to lessen the severity of dysmenorrhea, when menstruation resumes. However, dysmenorrhea can continue until menopause. 5–15% of women with dysmenorrhea experience symptoms severe enough to interfere with daily activities.^[13]

Secondary dysmenorrhea is the diagnosis given when menstruation pain is a secondary cause to another disorder. Conditions causing secondary dysmenorrhea include endometriosis, uterine fibroids, and uterine adenomyosis. Rarely, congenital malformations, intrauterine devices, certain cancers, and pelvic infections cause secondary dysmenorrhea.^[13] Symptoms include pain spreading to hips, lower back and thighs, nausea, and frequent diarrhea or constipation.^[16] If the pain occurs between menstrual periods, lasts longer than the first few days of the period, or is not adequately relieved by the use of non-steroidal anti-inflammatory drugs (NSAIDs) or hormonal contraceptives, women should be evaluated for secondary causes of dysmenorrhea.^{[10]:p. 379}

When severe pelvic pain and bleeding suddenly occur or worsen during a cycle, the woman or girl should be evaluated for ectopic pregnancy and spontaneous abortion. This evaluation begins with a pregnancy test and should be done as soon as unusual pain begins, because ectopic pregnancies can be life?threatening.^[17]

In some cases, stronger physical and emotional or psychological sensations may interfere with normal activities, and include menstrual pain (dysmenorrhea), migraine headaches, and depression.Dysmenorrhea, or severe uterine pain, is particularly common for young females (one study found that 67.2% of girls aged 13–19 have it).^[18]

The medications in the non-steroidal anti-inflammatory drugs (NSAIDs) class are commonly used to relieve menstrual cramps. Some herbs are also claimed to help.

Mood and behavior

Some women experience emotional disturbances starting one or two weeks before their period, and stopping soon after the period has started.^[4] Symptoms may include mental tension, irritability, mood swings, and crying spells. Problems with concentration and memory may occur.^[4] There may also be depression or anxiety.^[4]

This is part of premenstrual syndrome (PMS) and is estimated to occur in 20 to 30% of women. In 3 to 8% it is severe.^[3]

More severe symptoms of anxiety or depression may be signs of premenstrual dysphoric disorder (PMDD). Rarely, in individuals who are susceptible, menstruation may be a trigger for menstrual psychosis.

Bleeding

The average volume of menstrual fluid during a monthly menstrual period is 35 milliliters (2.4 tablespoons of menstrual fluid) with 10–80 milliliters (1–6 tablespoons of menstrual fluid) considered typical. Menstrual fluid is the correct name for the flow, although many people prefer to refer to it as menstrual blood. Menstrual fluid contains some blood, as well as cervical mucus, vaginal secretions, and endometrial tissue. Menstrual fluid is reddish-brown, a slightly darker color than venous blood.^{[10]:p. 381}

Unless a woman has a bloodborne illness, menstrual fluid is harmless. No toxins are released in menstrual flow, as this is a lining that must be pure and clean enough to have nurtured a baby. Menstrual fluid is no more dangerous than regular blood.

About half of menstrual fluid is blood. This blood contains sodium, calcium, phosphate, iron, and chloride, the extent of which depends on the woman. As well as blood, the fluid consists of cervical mucus, vaginal secretions, and endometrial tissue. Vaginal fluids in menses mainly contribute water, common electrolytes, organ moieties, and at least 14 proteins, including glycoproteins.^[19]

Many mature females notice blood clots during menstruation. These appear as clumps of blood that may look like tissue. If there are questions (for example, was there a miscarriage?), examination under a microscope can confirm if it was endometrial tissue or pregnancy tissue (products of conception) that was shed.^[20] Sometimes menstrual clots or shed endometrial tissue is incorrectly thought to indicate an early-term miscarriage of an embryo. An enzyme called plasmin – contained in the endometrium – tends to inhibit the blood from clotting.

The amount of iron lost in menstrual fluid is relatively small for most women.^[21] In one study, premenopausal women who exhibited symptoms of iron deficiency were given endoscopies. 86% of them actually had gastrointestinal disease and were at risk of being misdiagnosed simply because they were menstruating.^[22] Heavy menstrual bleeding, occurring monthly, can result in anemia.

Menstrual disorders

There is a wide spectrum of differences in how women experience menstruation. There are several ways that someone’s menstrual cycle can differ from the norm, any of which should be discussed with a doctor to identify the underlying cause:

There is a movement among gynecologists to discard the terms noted above, which although they are widely used, do not have precise definitions. Many now argue to describe menstruation in simple terminology, including:

• Cycle regularity (irregular, regular, or absent)
• Frequency of menstruation (frequent, normal, or infrequent)
• Duration of menstrual flow (prolonged, normal, or shortened)
• Volume of menstrual flow (heavy, normal, or light)^[23]

Dysfunctional uterine bleeding is a hormonally caused bleeding abnormality. Dysfunctional uterine bleeding typically occurs in premenopausal women who do not ovulate normally (i.e. are anovulatory). All these bleeding abnormalities need medical attention; they may indicate hormone imbalances, uterine fibroids, or other problems. As pregnant women may bleed, a pregnancy test forms part of the evaluation of abnormal bleeding.

Women who had undergone female genital mutilation (particularly type III- infibulation) a practice common in parts of Africa, may experience menstrual problems, such as slow and painful menstruation, that is caused by the near-complete sealing off of the vagina.^[24]

Premature or delayed menarche should be investigated if menarche begins before 9 years, if menarche has not begun by age 15, if there is no breast development by age 13, or if there is no period by 3 years after the onset of breast development.^[5]

Ovulation suppression

Birth control

Since the late 1960s, many women have chosen to control the frequency of menstruation with hormonal birth control pills. They are most often combined hormone pills containing estrogen and are taken in 28 day cycles, 21 hormonal pills with either a 7-day break from pills, or 7 placebo pills during which the woman menstruates. Hormonal birth control acts by using low doses of hormones to prevent ovulation, and thus prevent pregnancy in sexually active women. But by using placebo pills for a 7-day span during the month, a regular bleeding period is still experienced.

Injections such as depo-provera became available in the 1960s. Progestogen implants such as Norplant in the 1980s and extended cycle combined oral contraceptive pills in the early 2000s.

Using synthetic hormones, it is possible for a woman to completely eliminate menstrual periods.^[25] When using progestogen implants, menstruation may be reduced to 3 or 4 menstrual periods per year. By taking progestogen-only contraceptive pills (sometimes called the ‘mini-pill’) continuously without a 7-day span of using placebo pills, menstrual periods do not occur. Some women do this simply for convenience in the short-term,^[26] while others prefer to eliminate periods altogether when possible.

Some women use hormonal contraception in this way to eliminate their periods for months or years at a time, a practice called menstrual suppression. When the first birth control pill was being developed, the researchers were aware that they could use the contraceptive to space menstrual periods up to 90 days apart, but they settled on a 28-day cycle that would mimic a natural menstrual cycle and produce monthly periods. The intention behind this decision was the hope of the inventor, John Rock, to win approval for his invention from the Roman Catholic Church. That attempt failed, but the 28-day cycle remained the standard when the pill became available to the public.^[27]There is debate among medical researchers about the potential long-term impacts of these practices upon female health. Some researchers point to the fact that historically, females have had far fewer menstrual periods throughout their lifetimes, a result of shorter life expectancies, as well as a greater length of time spent pregnant or breast-feeding, which reduced the number of periods experienced by females.^[28] These researchers believe that the higher number of menstrual periods by females in modern societies may have a negative impact upon their health. On the other hand, some researchers believe there is a greater potential for negative impacts from exposing females perhaps unnecessarily to regular low doses of synthetic hormones over their reproductive years.^[29]

Breastfeeding