title: Onset of breast development in a longitudinal cohort.
abstract: OBJECTIVE
  There is growing evidence of pubertal maturation occurring at earlier ages, with many studies based on cross-sectional observations. This study examined age at onset of breast development (thelarche), and the impact of BMI and race/ethnicity, in the 3 puberty study sites of the Breast Cancer and the Environment Research Program, a prospective cohort of >1200 girls.
  
  
  METHODS
  Girls, 6 to 8 years at enrollment, were followed longitudinally at regular intervals from 2004 to 2011 in 3 geographic areas: the San Francisco Bay Area, Greater Cincinnati, and New York City. Sexual maturity assessment using Tanner staging was conducted by using standardized observation and palpation methods by trained and certified staff. Kaplan-Meier analyses were used to describe age at onset of breast maturation by covariates.
  
  
  RESULTS
  The age at onset of breast stage 2 varied by race/ethnicity, BMI at baseline, and site. Median age at onset of breast stage 2 was 8.8, 9.3, 9.7, and 9.7 years for African American, Hispanic, white non-Hispanic, and Asian participants, respectively. Girls with greater BMI reached breast stage 2 at younger ages. Age-specific and standardized prevalence of breast maturation was contrasted to observations in 2 large cross-sectional studies conducted 10 to 20 years earlier (Pediatric Research in Office Settings and National Health and Nutrition Examination Survey III) and found to have occurred earlier among white, non-Hispanic, but not African American girls.
  
  
  CONCLUSIONS
  We observed the onset of thelarche at younger ages than previously documented, with important differences associated with race/ethnicity and BMI, confirming and extending patterns seen previously. These findings are consistent with temporal changes in BMI.
authors.affiliation: Division of Adolescent Medicine, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave (ML-4000), Cincinnati OH 45229-3029. frank.biro@cchmc.org.
authors.forename: Frank M
authors.initials: FM
authors.lastname: Biro
authors.forename: Louise C
authors.initials: LC
authors.lastname: Greenspan
authors.forename: Maida P
authors.initials: MP
authors.lastname: Galvez
authors.forename: Susan M
authors.initials: SM
authors.lastname: Pinney
authors.forename: Susan
authors.initials: S
authors.lastname: Teitelbaum
authors.forename: Gayle C
authors.initials: GC
authors.lastname: Windham
authors.forename: Julianna
authors.initials: J
authors.lastname: Deardorff
authors.forename: Robert L
authors.initials: RL
authors.lastname: Herrick
authors.forename: Paul A
authors.initials: PA
authors.lastname: Succop
authors.forename: Robert A
authors.initials: RA
authors.lastname: Hiatt
authors.forename: Lawrence H
authors.initials: LH
authors.lastname: Kushi
authors.forename: Mary S
authors.initials: MS
authors.lastname: Wolff
mesh_terms: D000293:Adolescent; D000367:Age Factors; D015992:Body Mass Index; D001940:Breast / Q000254:growth & development*; D002648:Child; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D016014:Linear Models; D008137:Longitudinal Studies; D009519:New York City; D009820:Ohio; D011446:Prospective Studies; D011627:Puberty / Q000208:ethnology / Q000502:physiology*; D012495:San Francisco
keywords: breast development; girls; obesity; puberty