Background: Premature birth is associated with poor metabolic health in both sexes, potentially via earlier pubertal timing.
Methods: We examined the associations of gestational age and premature birth (<37 weeks gestation) with age at onset of puberty (Tanner stage II for breast or genitalia development). We used interval-censored survival analyses in 3963 boys and 3403 girls (93% follow-up) in a population-representative Chinese birth cohort, “Children of 1997,” comprising 88% of births in Hong Kong in April and May 1997. We also examined whether the associations varied with sex or with height or body mass index (BMI) at 7 years.
Results: Premature girls reached puberty about 4 months later than girls with ≥41 weeks’ gestation (time ratio = 1.04 [95% confidence interval = 1.01–1.06]), adjusted for mother’ age of menarche, mother's place of birth, and smoking during pregnancy. Gestational age was not associated with onset of puberty in boys (test for interaction by sex, P < 0.01). None of these associations was altered by adjustment for socioeconomic position or varied with childhood height or BMI.
Conclusions: Premature birth was not related to earlier onset of puberty; instead, premature girls had later onset of puberty. Thus, the association between premature birth and subsequent cardiovascular risk is probably not mediated through the timing of pubertal onset. It is unclear whether onset, duration, or tempo of puberty is more relevant to the detrimental consequences of early puberty. Further studies investigating intrauterine, infant, and childhood influences on the duration and tempo of puberty may help unravel the early origins of cardiovascular diseases.
From the Life course and Lifestyle Epidemiology Group, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, SAR, People's Republic of China.
Submitted 22 May 2011; accepted 14 November 2011.
This work is a sub-study of the “Children of 1997” birth cohort, which was initially supported by the Health Care and Promotion Fund, Health and Welfare Bureau, Government of Hong Kong [HCPF Grant # 216106] and re-established in 2005 funded by the Health and Health Services Research Fund [HHSRF Grants #03040771]. This sub-study was funded by the Health and Health Services Research Fund [HHSRF grants #07080751]. The authors reported no other financial interests related to this research.
Supplemental digital content is available through direct URL citations in the HTML and PDF versions of this article (www.epidem.com). This content is not peer-reviewed or copyedited; it is the sole responsibility of the author.
Correspondence to: C. Mary Schooling, 5/F William M.W. Mong Block, 21 Sassoon Road, Pokfulam, Hong Kong, Department of Community Medicine and School of Public Health, The University of Hong Kong, Pokfulam, Hong Kong, People's Republic of China. E-mail: firstname.lastname@example.org.