title: [Age of menarche and its relationship with body mass index and socioeconomic status].
abstract: BACKGROUND
  A decline in the age of menarche was observed from early 1900s to the 1970s. However, it is not known if a further decline occurred thereafter.
  
  
  OBJECTIVE
  To evaluate the age of menarche in girls from Santiago, Chile and its relationship with body mass index (BMI) and socioeconomic status.
  
  
  METHODS
  We studied 1302 healthy girls aged 7 to 19 years. Age of menarche was evaluated through a questionnaire to the patient and her parents. Kaplan-Meier curves were used to determine age of menarche and Cox regression analysis was employed to evaluate the effect of the type of school and BMI on the age of menarche.
  
  
  RESULTS
  The mean age at menarche was 12.7+/-0.04 years. Girls from public and private schools had their period at 12.5+/-0.1 and 13.05+/-0.05 years respectively. A negative correlation between z scores for BMI and age of menarche was observed (r-0.3: p =0.001). Girls whose menarche occurred before 11.5 years had higher z scores for BMI and a larger proportion were overweight, compared to girls who had menarche later. Cox regression analysis showed that after adjustment for BMI, age of menarche was similar in both types of schools.
  
  
  CONCLUSIONS
  Age of menarche is occurring three months earlier in girls from public schools, which is associated with higher z scores for BMI. Type of school, a marker of socio-economic status in Chile, affects timing of menarche due to differences in body mass index.
authors.affiliation: Instituto de Investigaciones Materno Infantil, Facultad de Medicina, Universidad de Chile, Casilla, Santiago, Chile.
authors.forename: M Isabel
authors.initials: MI
authors.lastname: Hernández
authors.forename: Nancy
authors.initials: N
authors.lastname: Unanue
authors.forename: Ximena
authors.initials: X
authors.lastname: Gaete
authors.forename: Fernando
authors.initials: F
authors.lastname: Cassorla
authors.forename: Ethel
authors.initials: E
authors.lastname: Codner
mesh_terms: D000293:Adolescent; D017668:Age of Onset; D015992:Body Mass Index; D002648:Child; D002677:Chile; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008572:Menarche / Q000502:physiology*; D009765:Obesity / Q000503:physiopathology*; D016016:Proportional Hazards Models; D012923:Social Class; D011795:Surveys and Questionnaires