Context: Recent studies have indicated that internationally adopted girls are at high risk of developing precocious puberty. Clinical studies including a contemporary control group are lacking.

Objective: To study clinical, biochemical and ultrasonographic markers of pituitary-gonadal activation in prepubertal adopted girls and a control-group in the same age categories.

Setting: University Hospital, Copenhagen, Denmark

Design and participants: Cross-sectional study of randomly selected internationally adopted girls ((N=99; mean age 6.9 (5.1-8.5) years) and controls of Danish origin (N=93; mean age 6.8 (5.2-8.5) years).

Methods: Height, weight and pubertal stage were assessed with serum levels of reproductive hormones. Size and morphology of internal genitals were evaluated by ultrasonography.

Results: Serum values of FSH were significantly higher in prepubertal adopted girls as compared to controls (median 1.4 (95% CI 0.4-3.6) IU/L vs.1.0 (0.4-2.4) IU/L, p<0.001). Serum estradiol was above detection limit (>18 pmol/L) in 46.5% of prepubertal adopted girls, and 20.7% of controls (p=0.001). In prepubertal adopted girls the proportion of measurable samples increased significantly with age (Odds Ratio (OR) 2.5 (95% CI 1.3-5.0, p=0.009). In controls the OR was 1.0 (0.6-1.7), p=0.9. Serum SHBG levels were significantly lower in prepubertal adopted girls compared to controls (99.0 (50.4-153.0) vs. 115.0 (53.1-202.1), p<0.001).

Conclusion: 5-8 years old adopted girls showed signs of increased pituitary as well as gonadal activity in spite of prepubertal phenotype in the majority of girls. Our findings suggest that early onset of puberty in adopted girls is centrally driven.