Factors associated with early age at menarche among Thai adolescents in Bangkok: A cross-sectional study

Background: 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. Methods: 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. Results: 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). Conclusion: 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.