title: Early age at menarche and wheezing in adolescence. The 1993 Pelotas (Brazil) birth cohort study.
abstract: OBJECTIVE
  To evaluate the effect of menarche before 11 years of age on the incidence of wheezing/asthma in girls 11 to 18 years of age.
  
  
  METHODS
  The study sample comprised 1,350 girls from a birth cohort that started in 1993 in the urban area of the city of Pelotas, southern Brazil; this cohort was followed until 18 years of age. We assessed wheezing by the question, "Have you ever had wheezing in the chest at any time in the past?," from the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire. Early menarche was defined as occurring before 11 years of age. We estimated the cumulative incidence of wheezing excluding from the analysis all those participants who reported wheezing before age of 11 years. We performed the chi-square test to assess the association between ever wheezing and independent variables. Poisson regression models with robust variance were used to estimate cumulative incidence ratios.
  
  
  RESULTS
  The average age at menarche in the cohort girls was 12 years (95% CI: 11.1-12.1). The prevalence of early menarche before 11 years of age was 11% (95% CI: 9.7-12.3). The cumulative incidence of wheezing from 11 to 18 years of age was 33.5% (95% CI: 30.9- 36.0). The crude association between ever wheezing in adolescence and early menarche before age 11 was 1.19 (95% CI: 0.96-1.48). After adjusting for early childhood and contemporaneous variables, no significant association for early menarche before 11 years of age and wheezing during adolescence was found (CIR: 1.18; CI95%: 0.93-1.49).
  
  
  CONCLUSIONS
  Early menarche before 11 years of age is not associated with an increased risk of wheezing during adolescence.
keywords: Pelotas; Wheezing; adolescents; asthma; cohort study; menarche