Abstract
Background:
The early onset of puberty may be related to obesity, so there is a need to know the prevalence of early pubertal milestones in nonoverweight children.

Objective:
We compared attainment of stage 2 breasts, stage 3 (sexual) pubic hair, and menarche in the Third National Health and Nutrition Examination Survey sample of children with normal BMI with those with excessive BMI (≥85th percentile).

Design/Methods:
The ages at which 5%, 50%, and 95% of youth had attained key pubertal stages were estimated by probit models. Logit models were then fit to compare attainment of these milestones in children of excessive and normal BMI.

Results:
Pubertal signs occurred before 8.0 years of age in <5% of the normal-BMI general and non-Hispanic white female population. However, pubertal milestones generally appeared earlier in normal-BMI non-Hispanic black and Mexican American girls; thelarche occurred before age 8.0 in 12% to 19% of these groups, and the 5th percentile for menarche was 0.8 years earlier for non-Hispanic black than non-Hispanic white subjects. Pubarche was found in ≤3% of 8.0-year-old girls with normal BMI of all of these ethnic groups but was significantly earlier in minority groups. Pubarche appeared before 10.0 years in <2% of normal-BMI boys. Girls with excessive BMI had a significantly higher prevalence of breast appearance from ages 8.0 through 9.6 years and pubarche from ages 8.0 through 10.2 years than those with normal BMI. Menarche was also significantly more likely to occur in preteen girls with an elevated BMI.

Conclusions:
Prevalence estimates are given for the key pubertal milestones in children with normal BMI. Breast and sexual pubic hair development are premature before 8 years of age in girls with normal BMI in the general population. Adiposity and non-Hispanic black and Mexican American ethnicity are independently associated with earlier pubertal development in girls.