title: Factors associated with early age at menarche among Thai adolescents in Bangkok: A cross-sectional study.
abstract: The age at menarche in the Thai population has not been determined since 1997. This study recruited adolescents in Bangkok Metropolis to determine the age at menarche and its associations with health and socioeconomic status.
  
  
  
  This cross-sectional study used a two-step stratified sampling strategy to recruit 1,020 female students, aged 10-16 years, from schools in Dusit district, Bangkok, Thailand. Self-reported data on age at menarche and social determinants of health were collected from participants and their parents. A trained research nurse collected anthropometric data.
  
  
  
  Mean age at menarche was 11.8 ± 1.0 years, and age at menarche was significantly correlated with year of birth (r = -0.4, p < 0.001). Students from schools that are part of Bangkok Metropolis had the lowest mean age at menarche. Participants born in 2000-2003 having their first period at < 11.8 years numbered 5.5 times (95% CI: 3.80-8.18) and 5.0 times (95% CI: 3.6-8.0) greater than those born in 1997-1999 by univariate and multivariate analysis, respectively. Year of birth significantly associated with age at menarche in univariate and multivariate analysis (p = 0.001).
  
  
  
  The mean age at menarche among female adolescents in Bangkok Metropolis was occurring earlier and was inversely associated with year of birth in this cohort. Only year of birth were associated with age at menarche in the multivariate regression models to adjust for potential confounders.
authors.affiliation: Department of Pediatrics, Faculty of Medicine, Vajira Hospital, Samsean Road, Dusit District, Bangkok, 10300, Thailand. pnoipayak@gmail.com.
authors.forename: Pongsak
authors.initials: P
authors.lastname: Noipayak
authors.affiliation: Department of Medicine, Faculty of Medicine Vajira Hospital, Navamindradhiraj University, Bangkok, 10300, Thailand.
authors.forename: Petch
authors.initials: P
authors.lastname: Rawdaree
authors.affiliation: Research Promoting Center, Faculty of Medicine Vajira Hospital, Navamindradhiraj University, Bangkok, 10300, Thailand.
authors.forename: Busaba
authors.initials: B
authors.lastname: Supawattanabodee
authors.affiliation: Research Promoting Center, Faculty of Medicine Vajira Hospital, Navamindradhiraj University, Bangkok, 10300, Thailand.
authors.forename: Sumonmal
authors.initials: S
authors.lastname: Manusirivitthaya
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D016015:Logistic Models; D008572:Menarche / Q000502:physiology*; D015999:Multivariate Analysis; D012574:Schools / Q000458:organization & administration / Q000706:statistics & numerical data; D011795:Surveys and Questionnaires; D013785:Thailand / Q000453:epidemiology
keywords: Age at menarche; Bangkok; Early puberty; Factors associated; Thai urban adolescents; Thailand