Declining age of puberty of school girls in southern Thailand

Background: Declines in the onset age of secondary sexual development have been reported in a number of recent studies in western and Asian countries. A study of Hat-Yai school girls in 1994 in Thailand showed that the ages at thelarche and menarche were 9.9 and 12.4 years, respectively. This study was to determine whether there was a decline in the average age of puberty in Hat-Yai school girls from 1994 to 2012. Methods: A cross-sectional study was conducted in 2140 healthy Hat-Yai school girls, aged 6-18 years, from June 2011 to March 2012. Breast and pubic hair development was assessed by the Tanner staging method. Probit analysis was used to calculate the median ages of different stages of breast and pubic hair development, and the age of menarche. Results: The median ages of girls having thelarche and menarche were 9.6 (95% CI, 9.4-9.8) and 12.2 (95% CI, 11.9-12.4) years, which declined from 9.9 (95% CI, 9.7-10.1) and 12.4 years (95% CI, 12.2-12.6) in the 1994 study respectively, however, without statistical significance. The youngest ages of girls who had breast stage 2 and menarche were 7.2 and 9.2 years, respectively. The final height at age 14 years in this cohort (157.3 cm) was 2.3 cm greater than that of girls in 1994 (155.0 cm). Conclusions: From 1994 to 2012, the age at onset of thelarche and menarche of girls in Hat-Yai municipality declined by 0.2 and 0.3 years, respectively. The earlier age at onset of puberty had no effect on final adult height.