Timing of pubertal onset in girls: evidence for non-Gaussian distribution.

CONTEXT The timing of the onset of puberty is considered to approximate a normal distribution. However, because many more girls present with early than late puberty, we hypothesized that the distribution of the timing of the onset of puberty in girls might have changed. OBJECTIVE/SUBJECTS: The objective of the study was to examine the distribution of the timing of the onset of puberty in normal Greek girls. DESIGN Onset of puberty, i.e. breast development (B2), was studied longitudinally in 311 prepubertal schoolgirls aged 6.4-8.2 yr until the onset of puberty. We also studied cross-sectionally 126 girls, 6-14 yr old. SETTING Clinical examinations took place in the school setting. RESULTS In the longitudinal study, median of the distribution of age at B2 was 10.0 yr (with the 25th and 75th centiles being 9.2 and 10.6 yr, respectively). Skewness was -0.45 (P=0.001), suggesting a negatively skewed distribution. In the cross-sectional study, 126 subjects were found at B2. The median of the age distribution at B2 was 10.1 yr (with the 25th and 75th centiles being 9.7 and 11.2 years, respectively). Skewness was -0.44 (P=0.03), suggesting a negatively skewed distribution. CONCLUSIONS A non-Gaussian distribution of the age at the onset of puberty in girls was documented. The currently used cutoff ages for precocious and delayed puberty may not be applicable to modern children; therefore, up-to-date studies on pubertal maturation are much needed.