Trend in Body Mass Index During Childhood in 460 Girls with Idiopathic Central Precocious Puberty

A secular trend toward earlier puberty onset in girls has been widely documented, with childhood overweight proposed as a contributing risk factor. This study aims to characterize body mass index (BMI) standard deviation score (SDS) trajectories over the six years preceding idiopathic central precocious puberty (CPP) onset in girls. This retrospective, single-center study included 460 girls diagnosed with idiopathic CPP in XXX between 2002 and 2022. The cohort was stratified into sporadic CPP, familial CPP, and CPP in internationally adopted girls. Clinical and demographic data were collected, and BMI trajectories were analyzed using piecewise mixed linear models. Pubertal onset (T0) was defined as Tanner stage B2. Among the 460 cases, 285 (62%) were sporadic, 145 (31.5%) familial, and 30 (6.5%) adoption-related CPP. Additionally, 11.7% were born small for gestational age (SGA). BMI SDS increased significantly during the six years preceding T0 across the entire cohort. The steepest rise occurred between six and three years before T0 (+0.21 SDS/year [95% CI: 0.13-0.29]), followed by a slower increase in the three years before T0 (+0.15 SDS/year [95% CI: 0.11-0.19]), and a subsequent stabilization post-T0 (+0.06 SDS/year [95% CI: -0.01-0.14]). The BMI increase rate was similar across all subgroups. Girls with idiopathic CPP show a significant prepubertal BMI SDS increase, with similar trajectories in sporadic and familial cases. The overrepresentation of SGA-born and adopted girls suggests that genetic and environmental factors may contribute to early pubertal onset. This study is the first to track BMI trajectories up to six years before idiopathic CPP onset in girls, revealing an early rise in BMI SDS across all subgroups (sporadic, familial, and adopted girls). Notably, SGA-born and adopted girls showed similar BMI patterns but were overrepresented in this CPP cohort.