<Tr> <Th> ICD - 10 </Th> <Td> E30 </Td> </Tr> <Tr> <Td_colspan="2"> (edit on Wikidata) </Td> </Tr> <P> Menarche (/ mɪˈnɑːrkiː / mi - NAR - kee; Greek: μήν mēn "month" + ἀρχή arkhē "beginning") is the first menstrual cycle, or first menstrual bleeding, in female humans . From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of fertility . </P> <P> Girls experience menarche at different ages . 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, but the magnitude of the decline and the factors responsible remain subjects of contention . The worldwide average age of menarche is very difficult to estimate accurately, and it varies significantly by geographical region, race, ethnicity and other characteristics . Various estimates have placed it at 13 . Some estimates suggest that the median age of menarche worldwide is 14, and that there is a later age of onset in Asian populations compared to the West . The average age of menarche is about 12.5 years in the United States, 12.72 in Canada, and 12.9 in the UK . A study of girls in Istanbul, Turkey, found the median age at menarche to be 12.74 years . </P>

What is the term for the onset of the first menstrual cycle