Endocrine Abstracts

Objective: Recent publications showing unexpectedly early breast development in American girls created debate worldwide. However, secular trend analyses are often limited by poor data comparability among studies done by different researchers in different time periods and populations. Here, we present new European data, systematically collected from the same region and by one research group at the beginning and end of the recent 15 year period.

Methods: Two thousand and ninety-five girls aged 5.6 to 20.0 years were studied in 1991–93 (1991-cohort, n=1100) and 2006–08 (2006-cohort, n=995). All girls were evaluated by palpation of glandular breast, measurement of height and weight and blood sampling (estradiol, LH and FSH). Age distribution at entering pubertal stages B2–B5, PH2–PH5 and menarche was estimated for the two cohorts.

Results: Onset of puberty, defined as mean estimated age at attainment of glandular breast tissue (Tanner stage B2+), occurred significantly earlier in the 2006-cohort (estimated mean age 9.86 years (95% confidence interval 9.70–10.01) when compared with the 1991-cohort (10.88 (CI 10.69–11.06)), P<0.0001. The difference remained significant after adjustment for BMI. Estimated ages at menarche were 13.42 (CI 13.24–13.60) and 13.13 (CI 12.95–13.31) in the 1991- and 2006-cohorts, respectively (P=0.023). The time between B2 and menarche increased from 2.54 years to 3.38 years. Serum FSH and LH did not differ between the two cohorts at any age interval, whereas significantly lower estradiol levels were found in 8–10 year old girls from the 2006-cohort compared to similarly aged girls from the 1991-cohort.

Conclusion: We found significantly earlier breast development and increased duration of the pubertal transition among girls born more recently. Alterations in reproductive hormones and BMI did not explain these marked changes, suggesting that other factors yet to be identified may be involved.