title: Secular trend in age at menarche in indigenous and nonindigenous women in Chile.
abstract: OBJECTIVE
  To estimate the secular trend in age at menarche, comparing indigenous and nonindigenous women, and its relationship with socio-demographic, family and nutritional factors.
  
  
  METHODS
  A study (historical cohorts) of 688 indigenous and nonindigenous women, divided into four birth cohorts (1960-69, 1970-79, 1980-89, and 1990-96) in an area in central southern Chile was carried out. Data and measurements were collected by health professionals using a previously validated questionnaire. Age at menarche was self-reported (recall). Adjusted differences among cohorts were estimated using a multivariate regression model.
  
  
  RESULTS
  A secular trend (P < 0.001) in age at menarche was found in both ethnic groups, with no significant differences between them (P > 0.05). In an adjusted model, a reduction in age at menarche was estimated at 3.7 months per decade between 1960 and 1990. This trend was moderated by higher socio-economic level, smaller number of siblings, and cohabitation with a single parent during infancy.
  
  
  CONCLUSIONS
  The trend has occurred in a steady progression over time in indigenous women, whereas in nonindigenous women, it was slow initially but has accelerated in recent years. Nonindigenous women have maintained a slightly lower age of menarche than their indigenous counterparts.
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine, La Frontera University, Temuco, Chile. xossa@ufro.cl
authors.forename: X M
authors.initials: XM
authors.lastname: Ossa
authors.forename: S
authors.initials: S
authors.lastname: Munoz
authors.forename: H
authors.initials: H
authors.lastname: Amigo
authors.forename: S I
authors.initials: SI
authors.lastname: Bangdiwala
mesh_terms: D000293:Adolescent; D017677:Age Distribution; D002648:Child; D002677:Chile; D015331:Cohort Studies; D003625:Data Collection; D005191:Family Characteristics / Q000208:ethnology*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008572:Menarche / Q000208:ethnology*; D009752:Nutritional Status / Q000208:ethnology*; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires