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Menstruation is the periodic discharge of blood and mucosal tissue (the endometrium) from the uterus and vagina. It starts at menarche at or before sexual maturity (maturation), in females of certain mammalian species, and ceases at or near menopause (commonly considered the end of a female's reproductive life). The periodicity of menstruation gives rise to commonly used euphemisms like "period" and "monthly".
Women typically stop menstruating if they conceive or if they are breastfeeding. When menstruation stops for longer than about 90 days in the absence of pregnancy or breastfeeding, a medical evaluation should occur, as a number of health problems can result in absent menstruation. Menstruation lasts from puberty until menopause among non-pregnant women.
The menstrual cycle involves the development of a nutrient-rich lining (namely the endometrium) within a woman's uterus that will cushion and nourish a developing fetus should impregnation occur. If pregnancy does not occur, this lining is released in what is known as menstruation, or a menstrual period.
Regular menstruation (also called eumenorrhea) lasts for a few days, usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal. The average menstrual cycle is 28 days long from the first day of one menstrual period to the first day of the next. A normal menstrual cycle in adult women is between 21 and 35 days.:p.381In adolescents, there is wider variation, and cycles are normally between 21 and 45 days. Menstrual symptoms occurring in the time prior to menstruation, such as breast pain, swelling, bloating, acne are termed premenstrual molimina .
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 menstrual flow, although many people prefer to refer to it as menstrual blood. Menstrual fluid in fact 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.:p.381
Unless the woman in question 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 depending 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. 
Many mature females also 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. 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 via menstrual fluid is relatively small for most women. 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. Heavy menstrual bleeding, occurring monthly, can result in anemia.
The first experience of a menstrual period occurs after the onset of pubertal growth, and is called menarche. The average age of menarche is around 12–13 (occurring earlier in girls of African descent than in white girls), but menarche can typically occur between ages 9 and 15. Premature or delayed menarche should be investigated; many older sources state that this should be done if menarche begins before 10 yrs or is delayed after 16 years,:p.381 while newer, more evidence-based sources state that it should be done if menarche begins before 9 yrs, 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. Perimenopause is when fertility in a female declines, and menstruation may occur 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 the late 40s and early 50s in Western countries.:p.381
In most women, various physical changes are brought about by natural fluctuations in hormone levels during the menstrual cycle, and by muscle contractions (menstrual cramping) involving the uterus that can precede or accompany menstruation. Some may notice water retention, changes in sex drive, fatigue, breast tenderness, or nausea. Breast swelling and discomfort may be caused by water retention during menstruation. Usually, such sensations are mild, and some people notice very few physical changes associated with menstruation. A healthy diet, reduced consumption of salt, caffeine and alcohol, and regular exercise may be effective for women in controlling these physical changes. The sensations experienced vary from person to person and from cycle to cycle. Severe symptoms that disrupt daily activities and functioning may be diagnosed as premenstrual dysphoric disorder.
Many women experience painful uterine cramps during menstruation. Pain results from ischemia and muscle contractions. Spiral arteries in the secretory endometrium constrict, resulting in ischemia to the secretory endometrium. This allows the uterine lining to slough off. The myometrium contracts spasmodically in order to push the menstrual fluid through the cervix and out of the vagina. The contractions are mediated by a release of prostaglandins. Dysmenorrhea is the medical term for painful periods.
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. 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. These drugs are typically more effective than treatments that do not target the source of the pain (e.g. acetaminophen). Risk factors for primary dysmenorrhea include: early age at menarche, long or heavy menstrual periods, smoking, and a family history of dysmenorrhea. Regular physical activity may limit the severity of uterine cramps.
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 dysmenorrhea patients experience symptoms severe enough to interfere with daily activities.
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. Symptoms include pain spreading to hips, lower back and thighs, nausea and frequent diarrhea or constipation. 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, patients should be evaluated for secondary causes of dysmenorrhea.:p.379
When severe pelvic pain and bleeding suddenly occur or worsen during a cycle, the patient should be evaluated for ectopic pregnancy and spontaneous abortion. This simple evaluation begins with a urinary pregnancy test and should be done as soon as unusual pain begins, because ectopic pregnancies can be life-threatening.
Some women experience emotional disturbances associated with their menstruation. These range from irritability, to tiredness, or "weepiness" (i.e. easily provoked tearfulness). A similar range of emotional effects and mood swings is associated with pregnancy. The prevalence of premenstrual syndrome (PMS) is estimated to be between 3% and 30%. More severe symptoms of anxiety or depression may be signs of premenstrual dysphoric disorder. Rarely, in individuals susceptible to psychotic episodes, menstruation may be a trigger (menstrual psychosis).
In some cases, stronger physical and emotional or psychological sensations may become debilitating, and include significant menstrual pain (dysmenorrhea), migraine headaches, and severe depression. Dysmenorrhea, or severe uterine pain, is particularly common for adolescents and young females (one study found that 67.2% of girls aged 13–19 suffer from it). This phenomenon is called premenstrual syndrome. More severe symptoms may be classified as premenstrual dysphoric disorder (PMDD).
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:
|Short or extremely light periods||Hypomenorrhea|
|Too-frequent periods (defined as more frequently than every 21 days)||Polymenorrhea|
|Extremely heavy or long periods (one guideline is soaking a sanitary napkin or tampon every hour or so, or menstruating for longer than 7 days)||Hypermenorrhea|
|Extremely painful periods||Dysmenorrhea|
|Breakthrough bleeding (also called spotting) between periods; normal in many people||Metrorrhagia|
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:
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.
Sexual intercourse during menstruation does not cause damage in and of itself, but the woman's body is more vulnerable during this time. Vaginal pH is higher and less acidic than normal, the cervix is lower in its position, the cervical opening is more dilated, and the uterine endometrial lining is absent, thus allowing organisms direct access to the blood stream through the numerous blood vessels that nourish the uterus. All these conditions increase the chance of infection and STI transmission during menstruation.
Sexual intercourse may also shorten the menstrual period. Some sources say that achieving orgasm helps the uterus contract and expel the lining. However, it is more likely that because semen contains luteinizing hormone (LH) and follicle stimulating hormone (FSH), and the vagina easily absorbs these hormones, the woman's hormone balance is slightly offset and the follicular phase of the menstrual cycle begins earlier. Similarly, levonorgestrel-releasing intrauterine devices and oral birth control pills alter the default hormone-release cycle, although by different mechanisms such as maintaining a high progestin level throughout a woman's cycle.
Menstruation is the most visible phase of the menstrual cycle, and corresponds closely with the hormonal cycle, and is therefore used as the limit between cycles; Menstrual cycles are counted from the first day of menstrual bleeding, a point in time commonly termed last menstrual period (LMP). The time from LMP until ovulation is, on average, 14.6 days, but with substantial variation both between people and between cycles in any single person, with an overall 95% prediction interval of 8.2 to 20.5 days.
During pregnancy and for some time after childbirth, menstruation is normally suspended; this state is known as amenorrhoea, i.e. absence of the menstrual cycle. 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.
Since the late 1960s, many women have chosen to control the frequency of menstruation with long-acting hormonal birth control, often simply called 'the pill'. 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 person menstruates. Hormonal contraception acts by using low doses of hormones to prevent ovulation, and thus prevent conception in sexually active women. But by using placebo pills for a 7-day span during the month, a regular bleeding period is still experienced.
Using synthetic hormones, it is possible for a person to completely eliminate menstrual periods. 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, the menstrual period is eliminated entirely. Some people do this simply for convenience in the short-term, 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. 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. These researchers believe that the higher number of menstrual periods experienced 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.
Something to absorb or catch menses may be used, and there are a number of different methods available.
In addition to products to contain the menstrual flow, pharmaceutical companies likewise provide products – commonly non-steroidal anti-inflammatory drugs (NSAIDs) – to relieve menstrual cramps. Some herbs, such as dong quai, raspberry leaf and crampbark, are also claimed to relieve menstrual pain.
Many religions have menstruation-related traditions; these may be bans on certain actions during menstruation (such as sexual intercourse in some movements of Judaism and Islam), or rituals to be performed at the end of each menses (such as the mikvah in Judaism and the ghusl in Islam). Some traditional societies sequester women in residences called "menstrual huts" that are reserved for that exclusive purpose.
In Hinduism, it is also frowned upon to go to a temple and do pooja (i.e., prayer) or do pooja at religious events if you are a woman who is menstruating. Saraswati, the Hindu goddess of knowledge, is associated with menstruation; the literal translation of her name is "flow – woman". Metaformic Theory, as proposed by cultural theorist Judy Grahn and others, places menstruation as a central organizing idea in the creation of culture and the formation of humans' earliest rituals.
Anthropologists, Lock and Nguyen (2010), have noted that the heavy medicalization of the reproductive life-stages of women in the West mimic power structures that are deemed, in other cultural practices, to function as a form of "social control." Medicalization of the stages of women's lives, such as birth and menstruation, has enlivened a feminist perspective that investigates the social implications of biomedicine’s practice. "[C]ultural analysis of reproduction…attempts to show how women…exhibit resistance and create dominant alternative meanings about the body and reproduction to those dominant among the medical profession."
All female placental mammals have a uterine lining that builds up when the animal is fertile, but it is dismantled when the animal is infertile. Most female mammals have an estrous cycle, yet only primates (including humans), several species of bats, and elephant shrews have a menstrual cycle. Some anthropologists have questioned the energy cost of rebuilding the endometrium every fertility cycle. However, anthropologist Beverly Strassmann has proposed that the energy savings of not having to continuously maintain the uterine lining more than offsets energy cost of having to rebuild the lining in the next fertility cycle, even in species such as humans where much of the lining is lost through bleeding (overt menstruation) rather than reabsorbed (covert menstruation).
Many have questioned the evolution of overt menstruation in humans and related species, speculating on what advantage there could be to losing blood associated with dismantling the endometrium rather than absorbing it, as most mammals do. Humans do, in fact, reabsorb about two-thirds of the endometrium each cycle. Strassmann asserts that overt menstruation occurs not because it is beneficial in itself. Rather, the fetal development of these species requires a more developed endometrium, one which is too thick to reabsorb completely. Strassman correlates species that have overt menstruation to those that have a large uterus relative to the adult female body size.
Beginning in 1971, some research suggested that menstrual cycles of co-habiting human females became synchronized. A few anthropologists hypothesized that in hunter-gatherer societies, males would go on hunting journeys whilst the females of the tribe were menstruating, speculating that the females would not have been as receptive to sexual relations while menstruating. However, there is currently significant dispute as to whether menstrual synchrony exists.