The association between socioeconomic status and the onset age of menarche is still not conclusive. This cross-sectional study was conducted among primary and middle school girls aged 7 to 16 years old in Tianjin, China, to explore the distribution of menarcheal age and its association with socioeconomic status. A self-designed structured questionnaire was completed by students and their parents to collect information on socioeconomic status (i.e., family income, parental education level, living residence), menarcheal status, and covariates (weight status of girls and their parents, sleeping hours per day, physical activity). Information on menarcheal status included whether or not menarche had occurred (Yes/No) and the exact age at menarche. Linear regression analysis was used to explore the association between socioeconomic status and menarcheal age before and after covariate adjustment. Among 1485 eligible girls with complete information, 445 had experienced menarche, with an overall menarche rate of 30%. The mean age at menarche was 12.9 years (95% confidence interval 12.8-13.0). Urban girls experienced menarche earlier than rural girls did (12.1 years vs. 13.5 years). Univariate analysis showed that urban residence and higher parental education were associated with earlier onset of menarche. After covariate adjustment, the significance still existed. However, after adjusting further for residence, the significant association with the parental education disappeared. Only urban residence was still significantly associated, even after further adjustment for parental education and family income, with adjusted regression coefficients (95% confidence interval) of - 1.087 (- 1.340,-0.834), indicating that the onset age of menarche among urban girls was 1.087 years (0.834, 1.340) younger than that among rural girls. Family income was not related to the onset age of menarche in any analyses.Conclusion: Urban-rural differences played a more important role in the early onset of menarche than socioeconomic differences between families. What is Known: • The age at menarche varies by race and country, but the global trend is towards earlier onset as a result of changes in nutrition, family structure, socioeconomic status, and physical condition. What is New: • Urban girls experienced menarche earlier than rural girls, but this urban-rural difference could not be explained by family income, parental education, weight status of the participants and their parents, participants' physical exercise and sleeping hours. • Higher parental education was associated with earlier onset of menarche, but this association disappeared after adjustment for living residence.
Keywords: China; Menarcheal age; School-age girls; Socioeconomic status; Urban-rural differences.