Trends and factors affecting secular change in age at menarche in Brazilian girls

The menarche presents relevant importance as a mark of growth and girls' maturation development and is the most indicator user to evaluate sexual maturity in girls. The knowledge of the age of sexual maturation's occurrence in determined population makes possible the analysis of trends in pubertal development of this population, beyond help to establishment of normative standards for the puberty. In such a way, the aim of the present study is analyses secular changes in girls' puberty, focusing on age at menarche and factors associates to this change in Brazilian girls. For the process of review secular trends in age at menarche was considered publications that was carried out after 1980. We found 15 studies about age at menarche that attends our criteria. Analyzing the age at menarche in the past decades, we observe a decrease in 14 months (12.97 to 11.49 years) in this period. Estimates that age at menarche will approach 11 years in 2010. The process of sexual maturation presents a variation in persons and populations that onset and process timing. Of the factors known to affect menarcheal timing, genetics via maternal tempo is the most obvious but it doesn't explain the secular trend, the gene pool has not had sufficient time to respond. Two other factors have been identified that affect menarche. The first is the child's size in childhood that have a relationship with menarcheal timing, the ‘critical weight hypothesis'. Other factor is the birth weight and nutrition in period pre-and/or postnatally. Improves in the assistance to health, urbanization and increase in socioeconomic status are factors associated to decrease undernutrition in childhood and recent rise in overweight and this factors are involved to menarcheal timing. What these factors are directly or more associated to this trends is a mystery and needs further work to know.