Should the UK use WHO growth charts?

Abstract

Growth reference charts are the basic assessment tool of child health whether at an individual, community, or national level. The comparison of a child's height or weight with the distribution of heights or weights of a reference sample provides evidence of the normality or otherwise of the process of growth. In the UK, the most widely used growth references are the UK1990 growth references (UK90). In 2006 the World Health Organisation launched the new chart and stated that, “The new growth curves are expected to provide a single international standard that represents the best description of physiological growth for all children from birth to five years of age and to establish the breastfed infant as the normative model for growth and development.” It is important to distinguish between a growth reference (e.g. UK90) and a growth standard (e.g. WHO 2006). Growth reference charts are usually based on cross-sectional data, they are for use with samples and they reflect growth “as is” rather than “as it ought to be”. Growth standards are a different tool – they are based on longitudinal data in which the source sample has been selected according to some pre-defined criteria and reflect growth not “as is” but growth “as it ought to be”. The Scientific Advisory Committee on Nutrition (SACN) recommended in 2007 that a modified WHO chart be adopted in the UK. These UK-WHO growth charts combined the UK90 data with the WHO data; the WHO data were used from birth to 4 years and the UK90 data from 4 years onwards. However, the WHO charts are standards not references and reflect the growth of children growing in unconstrained environments. Because they are longitudinal standards the WHO charts (particularly from birth to 2 years) should be used specifically for individuals rather than samples. They do not purport to represent the growth characteristics of the average child in a population and if used as a growth reference rather than a growth standard they will potentially provide conflicting and erroneous information. Tests of the UK-WHO chart in the UK indicate a good fit for length/height but a relatively poorer fit for weight because of slower weight gain in the WHO sample. Tests of the WHO charts from outside the UK recognise their usefulness for well-fed economically privileged children but recommend local growth charts when available. In addition, the vast majority of UK infants are not exclusively breastfed for anywhere near the recommended duration of 4 months and the duration of breastfeeding is heavily influenced by social and economic circumstances. It is, of course, the infants who live in social and economically deprived conditions, with young, poorly educated mothers who also have the greatest risk of growth faltering and for whom an accurate and appropriate growth assessment tool is of paramount importance. The choice of a growth chart clearly depends on the question being asked. Growth charts are not only tools but they are very specific tools designed to do a particular job. Their appropriate use requires training and education even though their appearance as relatively simple graphs of height or weight against age gives the impression of simplicity and a lack of sophistication. Indeed they are neither of these things. If the question relates to the growth of a child in comparison to breastfed infants living in socio-economic conditions that do not constrain growth then the WHO standard is the appropriate tool. If, on the other hand, the question relates to the growth of a child in comparison to other British children from no specific socio-economic background and with no specific feeding regime, then the UK90 will effectively answer the question. Of course, the WHO standard can be used in both situations but the probable absence of exclusive breastfeeding and perhaps the variation in socio-economic conditions within which the infant lives will necessarily alter the interpretation of the pattern of growth.