Small for gestational age and age at puberty: evidence from Hong Kong's "Children of 1997" birth cohort.

The predictive-adaptive response paradigm postulates that slow fetal growth advances puberty as a life-history strategy for reproductive success, when constraints on postnatal growth are minimal. The authors examined the association of birth weight for gestational age and small for gestational age (SGA) status (birth weight for gestational age 10th percentile, 6.9) with clinically assessed age at onset of Tanner stage II in a non-Western developed population using interval-censored regression in 7,366 children (89 follow-up) from a population-representative Chinese birth cohort, Children of 1997 in Hong Kong. Neither SGA status nor birth weight z score for gestational age was associated with age at onset of puberty, adjusted for sex, mothers place of birth, parental height, income, and parental education. Greater childhood height and linear growth were associated with younger age at onset of puberty. SGA status was associated with earlier puberty after adjustment for childhood height (time ratio 0.984, 95 confidence interval: 0.972, 0.995) but later puberty after adjustment for linear growth (time ratio 1.017, 95 confidence interval: 1.005, 1.030). In this developed city of China, SGA status was not associated with timing of puberty. However, the observation may be contextually specific depending on how other attributes, such as childhood growth, differ between SGA and other children.