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The timing of menarche is influenced by female biology, as well as genetic, environmental factors, and nutritional factors. [4] The mean age of menarche has declined over the last century, but the magnitude of the decline and the factors responsible remain subjects of contention.
Diagram illustrating how the uterus lining builds up and breaks down during the menstrual cycle Menstruation (also known as a period, among other colloquial terms) is the regular discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina. The menstrual cycle is characterized by the rise and fall of hormones. Menstruation is triggered by falling progesterone ...
Menstrual cycle The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible. The ovarian cycle controls the production and release of eggs and the cyclic release of estrogen and progesterone. The uterine cycle governs the preparation and maintenance of the lining of the ...
Menarche (the first menstrual cycle at puberty) is traditionally treated as a sign that the girl is probably ready for sex and marriage, as well as for adult duties in the household. Initiation rites on menarche include instruction on sex and marital relations as well as on menstrual management. This is conducted by older women.
The average age of a girl's first period is 12 to 13 (12.5 years in the United States, [6] 12.72 in Canada, [7] 12.9 in the UK [8]) but, in postmenarchal girls, about 80% of the cycles are anovulatory in the first year after menarche, which declines to 50% in the third year, and to 10% by the sixth. [9]
The age of thelarche has been decreasing in the past few decades. Between 1973 and 2013, the age of thelarche decreased at a rate of 0.24 years per decade. [9] Other contemporary trends that may be contributing to this change in the onset of thelarche include increasing BMI, changes in pubertal timing, and environmental exposures.
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Menarche, the beginning of menstruation, is a relatively late development which follows a long series of hormonal changes. [46] Generally, a girl is not fully fertile until several years after menarche, as regular ovulation follows menarche by about two years. [47]