Association of Infant Physical Development and Rapid Growth With Pubertal Onset Among Girls in Rural China.

Importance: Whether physical development and rapid growth during the first 2 years of life are associated with puberty onset in girls remains unclear. Objective: To examine the associations of infant physical development and rapid growth with the timing of puberty onset in girls. Design, Setting, and Participants: This prospective birth cohort study included girls whose mothers had participated in a randomized, double-blind cluster trial of micronutrient supplementation with a daily capsule of folic acid, iron and folic acid, or multiple micronutrients during pregnancy. A total of 547 singleton girls in rural western China who were born after 2004 were followed up at 3, 6, 12, and 24 months of age and were eligible for long-term follow-up. Of these, 294 adolescent girls (aged 10-12 years), representing 53.7% of the total sample, were included in the follow-up interview that was conducted from June 1 through December 31, 2016. Data analyses were conducted from November 1, 2019, to May 30, 2020. Exposures: Infant weight and length were assessed at birth and 3, 6, 12, and 24 months of age. Rapid growth, defined as a weight-for-age or length-for-age z score increase of greater than 0.67, was calculated during 5 periods: birth to 3 months, birth to 6 months, 6 to 12 months, 12 to 24 months, and birth to 24 months of age. Main Outcomes and Measures: Puberty stage was assessed using the standardized Tanner staging system. Onset of puberty was defined as attaining Tanner stage 2 of breast development or pubic hair growth, and the corresponding age at follow-up was recorded. Results: Of 294 girls included in the analysis (mean [SD] age, 11.25 [0.57] years), the median age of puberty onset was 11 (interquartile range, 10-11) years. A significant association with puberty onset was found for infancy weight-for-age z score at 12 months of age (adjusted hazard ratio [HR], 1.20; 95% CI, 1.01-1.44) and rapid weight gain from birth to 24 months of age (adjusted HR, 1.40; 95% CI, 1.01-1.93) and birth to 3 months of age (adjusted HR, 1.39; 95% CI, 1.02-1.91). However, length-related indicators during early life were not associated with adolescent puberty onset. Conclusions and Relevance: This study found that a higher weight-for-age z score and rapid weight gain during infancy, particularly from birth to 3 months of age, were associated with an increased likelihood of puberty onset in girls. These findings suggest that weight-related indicators may serve as proxies of puberty onset among adolescent girls.