SP1-79 Birth order, gestational age and birth weight and the age at onset of puberty: evidence from Hong Kong's “Children of 1997” birth cohort

Introduction Intrauterine and pubertal factors are associated with reproductive and cardiovascular health in both sexes. It is unclear how intrauterine exposures, birth order, gestational age and birth weight, also affect the timing of puberty. Methods We used interval-censored survival analyses in 3750 boys and 3241 girls (84% follow-up) in a Chinese birth cohort, “Children of 1997”, comprising 88% of births in Hong Kong in April and May 1997, to examine the adjusted associations of birth order, gestational age and birth weight with age at onset of puberty (Tanner stage II). We also examined whether the associations varied with sex or height at 7 years. Results Birth order and birth weight were unrelated to the age at onset of puberty, adjusted for sex, gestational age and socio-economic position. Gestational age had a sex-specific association with age at onset of puberty, and was associated with earlier onset among girls (Time Ratio 0.994, 95% CI 0.991 to 0.997) but not boys. None of these associations varied with childhood height. Conclusion Intrauterine exposures, as proxied by gestational age, birth order and birth weight, had little impact on the timing of the onset of puberty, which was only evident for gestational age among girls. Given that it is unclear whether onset, duration or intensity of puberty is more relevant to the detrimental consequences of early puberty, further studies investigating intrauterine, infant and childhood influences on the duration and intensity of puberty may help unravel the early origins of cardiovascular diseases and breast cancer.