WHO growth reference for children and adolescents

Summary of published research¹

The need for a widely applicable growth reference for older children and adolescents has increasingly been recognised by countries attempting to assess the magnitude of the growing public health problem of childhood obesity. This need has been reaffirmed by the recent release of the new under-five growth standards by the World Health Organisation (WHO) (see Field Exchange issues 28 and 30).

A paper has just been published which reports on a reconstruction of the 1977 National Centre for Health Statistics (NCHS)/WHO growth reference for older children. It compares the resulting new curves (the 2007 WHO reference) with the 1977 NCHS/WHO charts, and describes the transition at 5 years of age from the WHO references for under-fives to these new curves for school-aged children and adolescents.

The approach used in constructing the 2007 WHO reference addressed the limitations of the 1977 NCHS curves, recognised by the 1993 expert committee that recommended their provisional use for older children. The height-for-age median curves of the 1977 and 2007 references overlap almost completely with only a slight difference in shape. This is probably due to the different modelling techniques used. When compared to the 1977 NCHS/WHO curves, the differences in the newly reconstructed weightfor- age curves are significant in all centiles apart from the median and the -1 standard deviation (SD) curves. This reflects the important difference in curve construction methodology. The fact that the median curves of the two references overlap almost completely is reassuring in that the two samples used for fitting the models are the same within the healthy range (i.e. middle range of the distribution).

The reference data for Body Mass Index (BMI)-for-age recommended by WHO are limited in that they begin only at 9 years of age and cover a restricted distribution range (5th-95th percentiles). The 2007 reconstruction permits the extension of the BMI reference to 5 years, where the curves match WHO under-five curves almost perfectly (see table 1 for reference values). Furthermore, at 19 years of age, the 2007 BMI values for both sexes at +1 SD (25.4 kg/m2 for boys and 25.0 kg/m2 for girls) are equivalent to the overweight cut-off used for adults (25.0 kg/m2). The +2 SD value (29.7 kg/m2 for both sexes) compares closely with the cut-off for obesity (30.0 kg/m2).

The 2007 height-for-age and BMI-for-age charts extend to 19 years, which is the upper age limit of adolescence as defined by WHO. The weight-for-age charts extend to 10 years for the benefit of countries that routinely measure only weight and would like to monitor growth throughout childhood. Weight-for-age is inadequate for monitoring growth beyond childhood due to its inability to distinguish between relative height and body mass. Hence, the provision of BMI-for-age complements height-for-age in the assessment of thinness (low BMI-for-age), overweight and obesity (high BMI-for-age) and stunting (low height-for-age) in school-aged children and adolescents.

Growth reference data for children and adolescents aged 5-19 years (or 61-228 months) is available on the WHO website, http://www.who.int/growthref/en/

*WHO Child Growth Standards for 0-5 years of age.
**For BMI, the 1991 reference data start at 9 years of age.

¹Onis de M et al (2007). Development of a WHO growth reference for school-aged children and adolescents. Bulletin of the World Health Organisation, volume 85, No 9, pp 649- 732, September 2007. Available at http://www.who.int/bulletin/volumes/85/9/07-043497/en/print.html#R18#R18