Early menarche: Prevalence, predictors, outcomes

Menarche is a critical biomarker in the reproductive life of females. Recently, age at menarche is gaining attention as a considerable body of evidence shows that it has declined in the past century. Despite the downward trend in age at menarche and its implications for the wellbeing of women, there are still gaps in the literature in terms of its prevalence, predictors and health outcomes. Using two longitudinal studies, the "National Longitudinal Survey of Children and Youth" (NLSCY) from Canada and the "Cebu Longitudinal Health and Nutrition Survey" (CLHNS) from the Philippines, the dissertation aimed to examine: i) the epidemiology of age at menarche in Canada, ii) the potential role of breastfeeding on early menarche, iii) the impact of early menarche on asthma, and iv) the association between age at menarche on current smoking, heavy alcohol drinking and drug use. Using the NLSCY, results of the first objective estimated the mean and median of age at menarche in Canada as 12.72 years (SD= 1.05) and 12.67 years, respectively. The proportions of early (<11.53 years), average (11.53-13.91 years) and late maturers (>13.91 years) were 14.6% (95% confidence interval (CI): 11.9217.35), 68.0% (95% CI: 63.82-72.17) and 17.4% (95% CI: 14.10-20.63), respectively. Results from the CLHNS study for the second objective revealed that after adjusting for confounders, exclusive breastfeeding duration retained an independent and significant association with age at menarche. An increase in one month of exclusive breastfeeding decreased the hazard of attaining earlier menarche by 6% (hazard ratio: 0.94; 95% CI: 0.90-0.98). As for the third objective, it was shown from the NLSCY data that the onset of early menarche "11.56 years) predicted postmenarcheal incidence of asthma; girls who matured early had more than twice the risk of developing asthma during early adulthood than girls who matured at an average age (odds ratio, 2.34, 95% CI: 1.19-4.59). Finally in the last objective, no association was found between age at menarche and current practices of smoking, heavy drinking and drug use in the NLSCY. School performance and relationship with the father, however, emerged as the main variables associated with these substance use outcomes.