Size at birth, infant growth, and age at pubertal development in boys and girls

PURPOSE: This study investigated whether size at birth and infant growth were associated with age of indicators of pubertal development in boys and girls. We hypothesized that restricted fetal growth and accelerated infant growth lead to earlier pubertal age. PATIENTS AND METHODS: In total, 15,822 boys and girls answered questionnaires half-yearly with information on pubertal development: age at menarche, first ejaculation, voice break, Tanner stages, axillary hair, and acne. Birth weight and gestational age were used to calculate birth weight Z-scores. Changes in infant weight Z-score from 0 to 5, 5 to 12, and 0 to 12 months were estimated. We estimated the mean monthly difference in timing of puberty between children born small-for-gestational age (SGA) and large-for-gestational age (LGA) with children born appropriate-for-gestational age (AGA) as reference. We further investigated whether increasing infant weight Z-scores were associated with age at attaining indicators of pubertal development. RESULTS: Girls born SGA reached all pubertal markers at an earlier mean age than girls born AGA, as indicated by mean age differences below zero (eg, age at menarche: −2.3 months, 95% CI: −3.4, −1.2), except for breast development. Girls born LGA reached pubertal markers later than girls born AGA (eg, age at menarche: 1.7 months, 95% CI 0.5, 2.9). Boys born SGA and LGA achieved puberty earlier than boys born AGA, though with CIs crossing zero (eg, age at voice break for SGA: −0.7 months, 95% CI −2.1, 0.7 and for LGA: −0.7 months, 95% CI −2.1, 0.8). A 1-unit increase in weight Z-score from 0 to 12 months was associated with a mean age difference of −1.7 to −0.3 months for pubertal development in both sexes. CONCLUSION: Small size at birth and rapid infant growth were associated with early pubertal age, most consistent and pronounced in girls.