Gennemsnitsalderen for menarche er 12–15 år.<ref name=Jones2011/><ref>{{Cite journal  | last1 = Karapanou | first1 = O. | last2 = Papadimitriou | first2 = A. | title = Determinants of menarche. | journal = Reprod Biol Endocrinol | volume = 8 | issue =  | pages = 115 | year = 2010 | doi = 10.1186/1477-7827-8-115 | PMID = 20920296 }}</ref> Den kan dog i visse tilfælde begynde helt ned til otteårsalderen.<ref name=Women2014Men/> Denne første menstruation sker ofte senere i [[u-land]]e end i [[i-land]]e.<ref name=Diaz2006/> Faktorer såsom genetik, kost og overordnet sundhed kan påvirke timingen.<ref name=age>{{cite web | url = http://www.womenshealth.gov/publications/our-publications/fact-sheet/menstruation.cfm#f | title = At what age does a girl get her first period? | publisher = National Women's Health Information Center | access-date = 20. november 2011 | archive-date = 23. november 2011 | archive-url = https://web.archive.org/web/20111123084938/http://www.womenshealth.gov/publications/our-publications/fact-sheet/menstruation.cfm#f |url-status=dead }}</ref>
Psykologi Samfund Sexologi Sikkerhed Naturvidenskab