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In April 2006 the WHO released new child growth standards for infants and children up to the age of 5 years to replace the National Center for Health Statistics (NCHS) 1978 growth references(1) and the Centers for Disease Control and Prevention (CDC) 2000 growth charts(2) so far commonly used to assess the nutritional status of children in nutritional surveys all over the world(3,4). They are based on the WHO Multicentre Growth Reference Study(5-8), a population-based study conducted between 1997 and 2003 in about 8500 children from six different countries (Brazil, Ghana, India, Norway, Oman and the USA). Children were followed up longitudinally from 0 to 24 months with measurements at birth, weeks 1 to 4 and 6, then monthly from month 2 to month 12, and bimonthly in the second year. The data from 18 to 71 months were collected as cross-sectional data. The aim was to generate growth curves that represent the best description of physiological growth from birth to 5 years of age in breast-fed infants and establish the breast-fed infant as the normative model for growth and development. Consequently, only those children who were exclusively breast-fed for 4 months, acquainted with solid foods at 6 months and breast-fed throughout the whole first year of life were included (http://www.who.int/childgrowth/en/).
The NCHS 1978 growth references were the normalized version produced by the CDC based on the growth charts developed a year before by the NCHS. They were subsequently recommended by the WHO for international application and therefore used in nutritional surveys all over the world(9,10). This version made it possible to express height-for-age and weight-for-age in terms of standard deviations from the median or Z score(1,11,12). The NCHS standards were based on cross-sectional data from three National Health and Nutrition Examination Surveys and on the data from the Fels Study, a longitudinal study carried out from 1929 to 1975 in south-western Ohio by the Fels Research Institute (Yellow Springs, OH, USA). The Fels data were used to produce the charts for children less than 36 months of age. They came from a single regional population of mainly formula-fed, white, middle-class infants and were therefore...