Objectives: The purpose of this study was to examine the association of prepubertal body mass index (BMI) and weight status with pubertal development in boys and girls in Chongqing, China.

Methods: In a longitudinal study, 1237 students (695 boys and 542 girls) were recruited from Chongqing, China, and examined at baseline, then followed every 6 months for three and a half years. Height, weight, testicular volume, and breast development were measured at every examination. Age of first spermatorrhea and menarche were obtained from self-report. Subjects were divided into normal weight, overweight, and obese groups according to baseline BMI. Multivariable Cox regression analysis was used to examine the association of BMI and weight status with pubertal development.

Results: In girls, higher prepubertal BMI increased the chance of earlier menarche (hazards ratio (HR): 1.205, 95% confidence interval (95% CI): 1.151-2.261) and breast development (HR: 1.092, 95% CI: 1.045-1.142). Girls in the overweight (HR: 2.605, 95% CI: 1.716-3.956) and obese (HR: 2.565, 95% CI: 1.603-4.103) groups had an increased risk of early menarche compared with those in the normal weight group, while only overweight was associated with an increased risk for earlier breast development (HR: 1.469, 95% CI: 1.024-2.108). In boys, higher prepubertal BMI was significantly associated with the timing of first spermatorrhea (HR: 1.054, 95% CI: 1.004-1.106) and testicular development (HR: 1.098, 95% CI: 1.063-1.135). Overweight (HR: 1.672, 95% CI: 1.204-2.322) and obesity (HR: 1.598, 95% CI: 1.135-2.249) increased the hazard of earlier testicular development compared with the normal weight group, while no significant differences were detected among the three weight groups in terms of time to first spermatorrhea.

Conclusions: Higher prepubertal BMI was associated with earlier puberty in both Chinese boys and girls.