Menarche and adolescence

11. American College of Obstetricians and Gynecologists' Committee on Adolescent Health Care. Committee Opinion No. 651: Menstruation in girls and adolescents: using the menstrual cycle as a vital sign. Obstet Gynecol. 2015;126(6):e143–e146. doi:10.1097/AOG.0000000000001215Verified Endorsed by the American Academy of Pediatrics. Source of every adolescent parameter used on this site: median age at menarche between 12 and 13 years (median 12.43); 98% have started by 15, within 3 years of thelarche; threshold moves to 14 with hirsutism, disordered eating or excessive exercise; most bleed 2–7 days at the first menses; 90% of early cycles fall between 21 and 45 days; by the third year 60–80% are 21–34 days; and an interval of 90 days or more is the 95th percentile and uncommon even in adolescence. Also the origin of the menstrual-cycle-as-vital-sign framing.
12. Wang Z, Asokan G, Onnela JP, et al. Menarche and time to cycle regularity among individuals born between 1950 and 2005 in the US. JAMA Netw Open. 2024;7(5):e2412854. doi:10.1001/jamanetworkopen.2024.12854Verified Apple Women's Health Study, 71,341 US participants. Mean age at menarche fell from 12.5 years (born 1950–1969) to 11.9 years (born 2000–2005); early menarche before age 11 rose from 8.6% to 15.5% and very early menarche before age 9 from 0.6% to 1.4%; the proportion reaching cycle regularity within two years fell from 76% to 56%. In a subset providing BMI at menarche, roughly 46% of the decline was attributable to higher BMI. Self-recalled age in a non-population-representative app cohort — reported here alongside the ACOG statement rather than in place of it. Author list abbreviated; verify full order before formal citation.

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