Ethnic differences in the presence of secondary sex characteristics and menarche among US girls: The Third National Health and Nutrition Examination Survey, 1988-1994

Objective. To assess measures of puberty-presence of pubic hair, breast development, and menarche- for 3 racial/ethnic groups of girls in the United States. Methods. Using data from the Third National Health and Nutrition Examination Survey, this study sample was restricted to 1623 girls aged 8 to 16 years (466 non-Hispanic white, 589 non-Hispanic black, and 568 Mexican American) for whom information was available on Tanner stages of pubic hair and breast development. Subsequently, the sample was restricted to 1168 girls aged 10 to 16 years (330 non-Hispanic white, 419 non-Hispanic black, and 419 Mexican American) for whom menarche data were available. Tanner stage II or higher was used to define pubic hair and breast development; menarche status was self-reported. The percentage of girls who had pubic hair and breast development and had achieved menarche was computed by age and race/ethnicity. Probit and failure time models were applied to estimate mean ages at onset of pubic hair, breast development, and menarche. The racial/ethnic differences also were examined after adjustment for social and economic variables and current body mass index. Results. Black and Mexican American girls had pubic hair and breast development and had achieved menarche at younger ages than white girls. For example, 49.4% of black girls aged 9 years had breast development compared with 24.5% of Mexican American girls and 15.8% of white girls. The mean age at onset of pubic hair, breast development, and menarche was 9.5, 9.5, and 12.1 year for black girls; 10.3, 9.8, and 12.2 years for Mexican American girls; and 10.5, 10.3, and 12.7 years for white girls. These ethnic differences remained even after adjustment for current body mass index and several social and economic variables. Conclusion. Black girls on average enter puberty first, followed by Mexican American and then white girls.