menarche

 

Menarche (IPA: /məˈnɑrki/) is the first menstrual period, or first menstrual bleeding in the females of human beings. From both social and medical perspectives it is often considered the central event of female puberty, as it signals the possibility of fertility. Timing of menarche is influenced by both genetic and environmental factors, especially nutritional status. The average age of menarche has declined over the last century but the magnitude of the decline and the factors responsible remain subjects of contention. The average age of menarche in the United States is about 12 years and 6 months.

Physiologic aspects

Menarche as part of puberty

Menarche is the culmination of a series of physiological and anatomic processes of puberty, described in more detail in that article:

• Attainment of a sufficient body mass (typically 17% body fat PMID 3117838).
• Disinhibition of the GnRH pulse generator in the arcuate nucleus of the hypothalamus
• Secretion of estrogen by the ovaries in response to pituitary hormones.
• Over an interval of about 2 to 3 years, estrogen stimulates growth of the uterus (as well as height growth, breast growth, widening of the pelvis, and increased regional adipose tissue).
• Estrogen stimulates growth and vascularity of the endometrium, the lining of the uterus.
• Fluctuations of hormone levels can result in changes of adequacy of blood supply to parts of the endometrium.
• Death of some of the endometrial tissue from these hormone or blood supply fluctuations leads to deciduation, a sloughing of part of the lining with some blood flow from the vagina.

A specific hormonal signal for menarche is not known; menarche as a discrete event is thought to be the relatively chance result of the gradual thickening of the endometrium induced by rising but fluctuating pubertal estrogen.

The menstruum, or "flow", consists of a combination of fresh and clotted blood with endometrial tissue. The initial flow of menarche is usually brighter red than mature menstrual flow. It is often scanty in amount and may be very brief, even a single instance of "spotting". Like other menses, menarche may be accompanied by abdominal cramping.

Menarche and fertility

In most girls, menarche does not signal that ovulation has occurred. Studies of American girls suggest that the average interval between menarche and ovulation is several months. Irregular, anovulatory menses commonly occur for 1-2 years or more before regular ovulation is established.

Regular ovulation is usually indicated by predictable and consistent intervals between menses, predictable and consistent durations of menses, and predictable and consistent patterns of flow (e.g., heaviness or cramping). Continuing ovulation typically requires a body fat content of at least 22%. An anthropological term for this state of potential fertility is nubility.

On the other hand, not every girl follows the typical pattern and some girls have ovulated before the first menstruation. Although unlikely, it is possible for a girl engaging in sexual intercourse shortly before her menarche would occur to conceive and become pregnant, delaying her menarche until after the birth. This would be a rare exception to the widely held assumption that a woman cannot become pregnant until after menarche.

Effects of stress and social environment on timing of menarche

Some of the least understood environmental influences on timing of puberty are social and psychological. Nearly all of the research on these effects has concerned girls, partly because female puberty requires greater physiologic resources and partly because it involves a unique event (menarche) that makes survey research into female puberty much simpler than male. In most of these studies menarche was specifically examined, assuming it to be a valid "proxy" for the more general process of puberty. In comparison with the effects of genetics, nutrition, and general health, social influences are small, shifting timing by a few months rather than years. The most important part of a child's psychosocial environment is the family.

Some of the aspects of family structure and function reported to be independently associated with earlier menarche:

• The increased incidence of childhood obesity (reaching a body weight of 100 lbs or 45kg appears to be an important "trigger" for the very young reaching menarche--both estrogen and progesterone are fat-soluble hormones).
• Absence of father from the home from early childhood
• High conflict family relationships
• Living in an urban environment

Some of the aspects of family structure and function reported to be independently associated with later menarche:

• Larger family size
• Warmer, closer or more positive relationship with biological father
• Warmer, more supportive, low stress family environment
• Having a number of older sisters

Other research has focused on the effect of childhood stress on timing of puberty, especially female. Stress is a vague term and studies have examined conditions ranging from family tensions or conflict to wartime refugee status with threat to physical survival. The more dire social conditions have been found to be associated with delay of maturation, an effect that may be compounded by dietary inadequacy. There is more uncertainty and mixed evidence as to whether milder degrees of stress or early-life undernutrition can accelerate puberty in girls as would be predicted by life history theory and demonstrated in many other mammals.

The understanding of these environmental effects is incomplete and the following observations and cautions are relevant:

• Mechanisms of these social effects are unknown, though a variety of physiological processes, including pheromones, have been suggested based on animal research.
• Most of these "effects" are statistical associations revealed by epidemiologic surveys. Statistical associations are not necessarily causal, and a variety of covariables and alternative explanations can be imagined. Effects of such small size can never be confirmed or refuted for any individual child.
• Despite the small magnitude of effect, interpretations of the data are politically controversial because of the ease with which this type of research can be used for political advocacy. Accusations of bias based on political agenda sometimes accompany scientific criticism.

Changes over time in the average age of menarche

There were few systematic studies of timing of menarche before the latter half of the 20th century. Most older estimates of average timing of menarche were based on observation of a small homogeneous population not necessarily representative of the larger population, or based on recall by adult women, which is also susceptible to various forms of error. Most sources agree that average age of menarche in girls in modern societies has declined, though the reasons and the degree remain subjects of controversy. There have been claims of a 2 to 2.5 year decline from about 1900 to the 1960s, but the best North American surveys reported only a 2-3 month decline from the mid-1970s to the mid-1990s. This is commonly attributed to larger body size and earlier average attainment of sufficient body fat, but other factors such as environmental exposure to chemicals that mimic estrogen or the urbanization or "sexualization" of Western society have also been offered by some.

Less than 10% of US girls start to menstruate before 11 years of age, and 90% of all US girls are menstruating by 13.75 years of age, with a median age of 12.43 years. This age at menarche is not significantly different (0.34 years earlier) than that reported for US girls in 1973. Age at menarche for non-Hispanic black girls was significantly earlier than that of white girls at 10%, 25%, and 50% of those who had attained menarche, whereas Mexican American girls were only significantly earlier than the white girls at 25%. ^[1]

Cultural aspects of menarche

Menarche is celebrated in many cultures around the world as a rite of passage, a time to recognize that a girl is moving into womanhood.

Rites of passage

Some cultures have in past centuries have had rites of passage for a girl experiencing menarche.

• In the United States, rites of passage are rare since girls are taught to keep aspects of sexual development private. However, some families celebrate by giving the girl a card of congratulations, or even a candlelight ceremony.

• The Navajo Indians have a celebration called kinaalda (kinn-all-duh). Girls run footraces to show strength. A cornmeal pudding is made for the tribe to taste. The girls who experience menarche wear special clothes and style their hair like the Navajo goddess "Changing Woman".

• The Nootka Indians thought menarche was a time for a physical strength test. The girl is taken out to sea and left there. She is to swim back and when she returns to the shore of the village, she is cheered.

• The Mescalero Apaches consider their menarche celebration the most important. Each year, an 8-day-long ceremony is celebrated in honor of each girl who began their period that year. The first 4 days include of feasting and dancing. Boy singers recount the history of the tribe each evening. The other four days are a private celebration where girls have a private ceremony, reflecting on passing into womanhood.

• In Australia, the Aborigines treated a girl to "love magic". The women teach her of the female powers and the physical changes marking womanhood.

• When a Japanese girl has her first period, the family celebrates by eating red colored rice and beans.

• The Ulithi (oo-lith-ee) tribe of Micronesia call a girl's menarche kufar (koo-faar). She goes to a menstrual house where the women bathe her and recite spells. The girl will go back to the menstrual house when her next period comes.

• In Nigeria in the Tiv tribe, four lines are cut in her abdomen, being thought to make her a woman and more fertile.

• Sri Lanka notes the time and day. An astrologer is contacted, who studies the star's alignment at the noted moment. This is done to predict the girl's future. Her house is prepared for a ritual bathing, where the girl is scrubbed all over by the women of the family. She then is dressed in white. Printed invitations for a party are sent out, where the girl receives money and special gifts.

Medical aspects of menarche

When menarche occurs, it confirms that the girl has had a gradual estrogen-induced growth of the uterus, especially the endometrium, and that the "outflow tract" from the uterus, through the cervix to the vagina, is open.

In very rare instances, menarche may occur at an unusually early age, preceding thelarche and other signs of puberty. This is termed isolated premature menarche, but other causes of bleeding must be investigated and excluded. Growth is usually normal. ^[2] Isolated premature menarche is rarely the first manifestation of precocious puberty.

When menarche has failed to occur for more than 3 years after thelarche, or past 16 years of age, the delay is referred to as primary amenorrhea.

See also

• Puberty for a more detailed discussion of factors affecting timing
• Delayed puberty
• Precocious puberty
• Thelarche
• Adrenarche
• Pubarche
• Gonadarche
• Menstrual cycle
• Lina Medina, who had her first menarche at age 8 months and is the youngest mother in history.

References

Further reading

• Quinlan, R. (2003). Father-Absence, Parental Care & Female Reproductive Development. Evolution & Human Behavior. 24(6): 376-390. Full text

External links

• Mark Hanson, P. Gluckman. Evolution, development and timing of puberty, Trends in Endocrinology & Metabolism, January 2006.
• [1] Discusses some of the social influences

Physiology, endocrinology, sex: Reproductive physiology and endocrinology
Menstrual cycle/Estrous cycle	Menstruation - Follicular phase - Ovulation - Luteal phase
Gametogenesis	Spermatogenesis -Oogenesis
Sexuality	Human sexual behavior - Sexual intercourse - Erection - Ejaculation - Orgasm - Insemination - Fertilisation/Fertility - Masturbation - Pregnancy - Postpartum period
Lifespan	Prenatal development - Sexual dimorphism - Sexual differentiation - Puberty (Menarche, Adrenarche) - Maternal age/Paternal age - Climacteric (Menopause, Andropause)
Eggs	Oviposition - Oviparity - Ovoviviparity - Viviparity

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