Are universal standards for optimal infant growth appropriate? Evidence from a Hong Kong Chinese birth cohort
- 1Department of Community Medicine and School of Public Health, The University of Hong Kong, Hong Kong, People’s Republic of China
- 2Department of Health, The Government of Hong Kong Special Administrative Region, Hong Kong, People’s Republic of China
- C Mary Schooling, The University of Hong Kong, Department of Community Medicine, 5/F William MW Mong Block, Room 5-21, 21 Sassoon Road, Pokfulam, Hong Kong, People’s Republic of China;
- Accepted 31 May 2007
- Published Online First 7 June 2007
Objective: In 2006 the World Health Organization (WHO) published new optimal growth standards for all healthy infants worldwide. To assess their general applicability to a recently transitioned Chinese population, we compared them with infant growth patterns in a representative sample of Hong Kong infants.
Design and settings: Weight at birth and at 1, 3, 9, 12, 18 and 36 months, length at 3 and 9 months and height at 36 months were obtained for over 80% of all infants born in April and May 1997 (3880 boys and 3536 girls). Age and sex specific z scores were calculated relative to the WHO growth standards for term singletons.
Results: Weight for age was close to the 50th percentile of the WHO growth standards for both boys (mean z score: 0.00) and girls (0.04) at most time points before 3 years of age. However, our participants were shorter at 3 years, where the z scores in height were −0.34 and −0.38 for boys and girls, respectively. Restricting the analysis to a subset matching the WHO criteria for healthy infants without restrictions on growth gave similar results.
Conclusions: Although the WHO study group concluded there was a striking similarity in length/height among different populations, Hong Kong Chinese toddlers are, on average, shorter. Epigenetic constraints on growth coupled with the rapid epidemiological transition in Hong Kong may not have allowed sufficient generations for infants and children to reach their full genetic height potential, and with it the WHO standards. A universal infant growth standard may not be appropriate across all populations.
Funding: This study was supported by the Hong Kong Health Care and Promotion Fund (grant no. 216106) and the Health and Health Services Research Fund (grant no. 03040771), Hong Kong, China.
Competing interests: None.