RESUMEN
STUDY OBJECTIVE: The aim of this study was to measure the prevalence of premature thelarche in infant and toddler girls and to determine if environmental sources of estrogen were associated with early breast development. DESIGN: Observational with mixed methods: Retrospective chart review, cross-sectional component involving an interview survey, along with longitudinal follow-up of girls with thelarche up to six months. SETTING: A general pediatric clinic within a teaching hospital located in a large Midwestern city. PARTICIPANTS: Girls, between the ages of 12 and 48 months, and their mothers, presenting for well-child care. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Prevalence of premature thelarche; association of premature thelarche with selected environmental exposures. RESULTS: Among the 318 subjects, the overall prevalence of premature thelarche was measured at 4.7% (n = 15). The prevalence by race/ethnicity was 4.2% among White Non-Hispanics, 4.6% among Blacks and 6.5% among White Hispanics. The peak prevalence occurred between 12-17 months of age. All thelarche cases were Tanner stage 2. No statistically significant relationship was found between premature thelarche and environmental exposures. Upon follow-up, 44% of the cases of premature thelarche had persistent breast development. CONCLUSIONS: Our study demonstrated a higher prevalence of premature thelarche than has been previously reported. This study lacked power because of the small number of premature thelarche cases, the ubiquitous presence of environmental exposure as well as the potentially small effect of each environmental factor. Future studies need to employ a very large sample in order to accurately analyze the relationship between environmental toxicants and premature thelarche.