Are universal standards for optimal infant growth appropriate? Evidence from a Hong Kong Chinese birth cohort

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.