menarche

n. beginning of menstruation

Menarche 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.
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Menarche /me·nar·che/ establishment or beginning of the menstrual function.menar´cheal me·nar·che n. [more]Menarche - Community and Resources

Noun
1. the first occurrence of menstruation in a woman
(hypernym) start

n. menarche, beginning of menstruation