The first menstrual period and marks the completion of a girl’s stepwise progression through puberty to sexual maturity,

Menarche is the first menstrual cycle, or first menstrual bleeding, in females.

It is often considered the central event of female puberty, as it signals the possibility of fertility.

Having menarche occur between the ages of 9–16 is considered normal.

Marks the time that a female is capable of becoming pregnant.

The age of menarche has decreased significantly over the last 150 years.

The timing of menarche is influenced by female biology, as well as genetic and environmental factors, especially nutritional factors. 

The mean age of menarche has declined over the last century.

The average age of menarche varies significantly by geographical region, race, ethnicity and other characteristics: 

Various estimates have placed it at 13.

The decline in age of menarche is observed and felt to be primarily attributed to deterioration in lifestyle factors and environmental toxic agents.

The earlier the menarche the shorter the adult stature.

There is a later age of onset in Asian populations compared to the West.

Menarche is the culmination of a series of physiological and anatomic processes of puberty.

It occurs at the attainment of a sufficient body mass, which is typically at 17% body fat.

There is disinhibition of the GnRH pulse generator in the arcuate nucleus of the hypothalamus.

Secretion of estrogen by the ovaries in response to pituitary hormones occurs.

With menarche and over an interval of about 2 to 3 years, estrogen stimulates growth of the uterus, height growth, breast growth, widening of the pelvis, increased regional adipose tissue, and growth and vascularity of the endometrium.

No specific hormonal signal for menarche exists.

Menarche is thought to be the result of the gradual thickening of the endometrium induced by rising but fluctuating pubertal estrogen.

The menstrual flow, consists of a combination of fresh and clotted blood with endometrial tissue. 

The initial flow of menarche is usually brighter than mature menstrual flow, and is often scanty in amount and may be very brief, even a single instance of “spotting”. 

Menarche may be accompanied by abdominal cramping.

Menarche does not mean that ovulation has occurred. 

In postmenarchal girls, about 80% of the cycles  are  anovulatory in the first year after menarche, 50% in the third and 10% in the sixth year.

The onset of  regular ovulation is usually indicated by predictable and consistent intervals between menses, predictable and consistent durations of menses, and predictable and consistent patterns of  menstrual flow.

Continuing ovulation typically requires a body fat content of at least 22%. 

The state of potential fertility is nubility.

Some girls ovulate before the first menstruation, opposing the widely held assumption that a woman cannot become pregnant until after menarche.

Very rarely menarche may occur at an unusually early age, preceding thelarche and other signs of puberty: isolated premature menarche.

Isolated premature menarche is rarely the first manifestation of precocious puberty.

Menarche failing to occur for more than three years after thelarche, or beyond 16 years of age,  delay is referred to as primary amenorrhea.

Systemic or chronic illnesses can delay menarche, such as undiagnosed and untreated celiac disease, asthma, diabetes mellitus type 1, cystic fibrosis and inflammatory diseases.

Early age at menarche is a risk factor for the insulin resistance condition.

Factors associated with earlier menarche:

Being non-white

Having experienced pre-eclampsia in the womb

Being a singleton

Low birthweight

Not having been breast-fed

Previous exposure to smoking

High-conflict family relationships

Increased incidence of childhood obesity.

Lack of exercise in childhood

Dire social conditions have been found to be associated with delay of maturation, an effect that may be compounded by dietary inadequacy. 

Fewer than 10% of U.S. girls start to menstruate before 11 years of age, and 90% of all U.S. girls are menstruating by 13.8 years of age, with a median age of 12.4 years. 

Menstruation is a cultural as well as scientific phenomenon.

Menstruation in many societies has specific rituals and cultural norms associated with it. 


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