WHO Growth Charts, Part 3

WHO has recently published the first set of  results from its Multicentre Growth Reference Study (MGRS). The full version  is available on the web at www.who.int/childgrowth/standards/technical_report/en/index.html and a series of related papers has been published in Acta Paediatrica 2006; Suppl 450:7-101 – details have already been mentioned on this website.  

IFM presents three papers concerning the report, all of which have been prepared by members of IFM’s Advisory Committee on Child Health and Nutrition:

1. Introduction and Summary
2. Implications for the Developed World and Comparisons with Other Growth Charts
3. Implications for Developing Countries

Part III: Implications for Developing Countries

Adequate nutrition during early years of life is of paramount importance for growth, development and long term health through adulthood. It is during infancy and early childhood that irreversible faltering in linear growth and cognitive deficits occur. Poor nutrition during this critical period contributes to significant morbidity and mortality in developing countries. Although breastfeeding is common in these regions, especially in Southeast Asia, inadequate and delayed complementary feeding leads to growth failure in young children. Early detection of growth faltering and promotion of appropriate feeding practices are important for prevention of malnutrition and the very survival of children.
 
Strategy for infant and young child feeding
The Global Strategy for Infant and Young Child Feeding was developed by the WHO and UNICEF in 2003 (1). It provides a comprehensive framework for promoting appropriate feeding practices and reducing malnutrition. The strategy recommends that infants should be exclusively breastfed for the first six months of life and thereafter, should receive adequate and safe complementary foods while breastfeeding is continued for two years or beyond.

The transition from exclusive breastfeeding to complementary feeding, covering the period from 6-24 months of age, is the most vulnerable period, when growth faltering starts in many children. Many factors contribute to malnutrition in the complementary feeding period. These include late introduction, poor nutritional quality and insufficient amounts of complementary foods. Early introduction of complementary foods may displace breast milk and increase the risk of infection. Frequent infections affect appetite and further reduce food intake resulting in growth failure. Promotion of breastfeeding and appropriate complementary foods is important for achieving optimal growth and development of children.

Assessment of child growth
Anthropometric measurements are commonly used for assessing growth and nutritional status of children (2). These include weight for age, height for age and weight for height. Although the prevalence of low weight for age and height for age are often used interchangeably to describe chronic malnutrition, they provide very different information on what the problem is, how it can be remedied and the age when this is possible. Low height for age reflects the cumulative effects of numerous insults experienced by children during infancy and early childhood. It begins at birth and continues through the initial 40 months, after which time it is irreversible. In contrast, low weight for age is reversible, and can reflect either acute or chronic malnutrition. Children with acute malnutrition require different nutrition and health interventions than those with chronic malnutrition.

Throughout the developing world, children fail to grow in length and weight in a remarkably similar age-specific pattern, despite vast differences in the prevalence of low wt/age and ht/age between the regions (3). Faltering in length extends through the first 3 to 4 years of life. In contrast, faltering in weight is concentrated between 3 and 12 months. After 12 months of age, a child may be stunted and of low wt /age, but his wt/ht ratio improves. In other words, weight gain can be adequate even while the process of stunting continues for another two years. While failure to gain weight is a signal of inadequate nutrition, adequate weight gain does not necessarily mean that a child is growing normally.

Thus the differences in the degree of growth failure in weight and height have implications for assessing the true prevalence of chronic malnutrition. This is also important for monitoring trends or evaluating the effects of interventions (4). Weight distribution, when corrected for height, may be normal or shift towards the right, indicating a tendency toward over weight among children who are stunted. There is a need to shift the focus from wt/age to ht/age and wt/ht for assessing malnutrition and identifying populations that could benefit from interventions.

Child growth standards
Anthropometric assessment involves the use of growth standards. They provide a useful tool for assessing nutritional status and well being of children. The terms growth standard and growth reference are used interchangeably, though their meaning is different. A standard reflects an optimum level, suggesting that all children have the potential to achieve that level, while growth reference is simply used for comparison. The  WHO/NCHS growth reference is widely used all over the world (2). However, its limitations are well recognized. The growth reference is based on formula fed children from a single community in the US. The children were measured every three months, which is not adequate to describe the rapid and changing rate of growth in early infancy.

There are several studies to show that growth pattern of breast fed infants is different from that of formula fed infants and the current growth reference. For example, in a longitudinal study of American infants, weight for length z-scores were significantly lower in breast fed than formula fed infants from 7-24 months (5). Triceps and sub-scapular skin folds and % body fat were also lower indicating that breast fed infants are leaner compared to their formula fed counterparts. The WHO working group on infant growth reviewed the available data on breast fed infants; who were exclusively breast fed for at least 4 months and continued breastfeeding for 12 months (6). Analysis of pooled data set showed that growth curves of breast fed infants deviated significantly from the NCHS references, suggesting that these standards are not appropriate for assessing physiological growth of healthy infants. There is a need for international growth standards that will show how children should grow in all settings, rather than reflect growth pattern of children in a specific population. Recognition of this fact has led to the development of new growth standards

WHO Multi-center Growth Reference Study
The WHO conducted a multi-center study and collected growth data and related information on about 8500 children from diverse ethnic backgrounds and cultural settings (7,8). The participating countries include Brazil, Ghana, India, Norway, Oman, & United States. The data was collected by trained staff using a common protocol. The study was designed to combine a longitudinal follow up of children from birth to 24 months and a cross sectional study of children aged 18 to 71 months. Children were selected from communities where there were no environmental constraints to growth. They were healthy term infants who had no known illness or conditions that might affect their growth, and were breast fed as per the international feeding guidelines. The new growth reference is based on breastfeeding as the biological norm. The measurements include weight/age, height/age and weight/height. Data on BMI was generated for children under 5 yrs for the first time. Other measurements include head circumference, mid-arm circumference, triceps and sub-scapular skin folds. Current references do not provide values for these parameters. In addition, key motor milestones like sitting, standing and walking were measured, linking motor development to physical growth.

The WHO report on new growth standards was released on 27 April 2006. It provides details of the growth study including study design and methodological process followed for development of growth standards. The report presents the first set of data on length and height/age, weight/age, weight/length, weight/height and BMI. It also provides comparison between the new standards and NCHS growth references. There are differences not only in the populations used, but also in the methodologies applied to construct the two sets of growth curves.

The data showed great similarities in growth across all study centers (8, 9). The new standards demonstrate that child populations in different regions of the world have the same growth potential. They can attain the same heights and weights when their health care needs are met. However, the new standards apply to children from birth to 5 years. Genetic influence on the ultimate height in adulthood can not be ruled out.

Differences between the new standards and NCHS references
As expected, there are important differences between the new standards and NCHS references. However, these vary/by age, sex, anthropometric measure and specific percentile or z- score curve. Differences are particularly important in infancy. Impact on population estimates of child malnutrition will depend on age, sex, anthropometric indicator considered and population-specific anthropometric characteristics. Thus, it will not be possible to provide an algorithm that will convert the prevalence values, from old to the new. In the past, the growth of breast fed infants after the first three months was judged as inadequate using the old NCHS reference. The new charts may now classify more formula fed infants as over weight. A notable effect is that stunting will be greater throughout childhood when assessed using the new WHO standards compared to the previous international reference. For wasting, the main difference between the new standards and the old reference is during infancy, up to about 70 cm length, when wasting rates will be substantially higher using the new WHO standards. With respect to overweight, use of the new WHO standards will result in a greater prevalence that will vary by age, sex and nutritional status of the index population.

Summary
The growth charts based on the new WHO standards differ from the existing standards in many innovative ways. They describe ‘how children should grow’, which is a prescriptive approach, not just a descriptive one. They show that all children can attain a similar standard of height and weight with adequate feeding and health care. It is a more pro-active way of evaluating child growth. A key characteristic of the new standard is that it establishes breastfeeding as the biological norm. Furthermore, the pooled sample from the six participating countries creates a truly international standard, in contrast to the previous growth reference based on children from a single country. The new growth standards go beyond the current references and include new indicators like BMI and skin folds. These charts will be particularly useful in monitoring childhood obesity, which is relevant to both developed and developing countries. Poor growth during infancy leads to childhood malnutrition in many developing countries, which if followed later in life by an increased intake of calories could result in overweight or obesity. It is not uncommon to see an under-nourished child in the same household as an overweight adult. 

The standards provide an effective tool for detecting both under nutrition and obesity, thus addressing the double burden of malnutrition. The growth charts will be useful to nutritionists, pediatricians and other health professionals concerned with child care.

References

1. Global Strategy for Infant and Young Child Feeding. WHO/UNICEF. World Health Organization. Geneva. 2003.
2. Waterlow JC et al. The presentation and use of height and weight data for comparing the nutritional status of groups of children under the age of 10 years. Bull World Health Organ 1977;/55:/489_/98
   3. Shrimpton R et al. Worldwide timing of growth faltering: implications for nutrition interventions. Pediatrics 2001; 107:1-7.
3. Chessa Lutter. Meeting the challenge to improve complementary feeding. SCN News # 27; December 2003; P 4-9.
4. Dewey KG et al. Breast fed infants are leaner than formula fed infants at 1 yr of age: the DARLING study. Am J Clin Nutr 1993;57:140. 
5. WHO Working Group on Infant Growth. An evaluation of infant growth: The use and interpretation of anthropometry in infants. Bull World Health Organ 1995;73:165.
6. de Onis M et al. For the WHO Multcentre Growth Reference Study Group. Measurement and standardization protocols for anthropometry used in the construction of a new international growth reference. Food Nutr Bull 2004;25 Suppl 1:S27_/36.
7. WHO Multicentre Growth Reference Study Group. WHO Child Growth Standards: Length/height-for-age, weight-for age, weight-for-length, weight-for-height and body mass index-for-age: Methods and development. Geneva: World Health Organization; 2006.
8. WHO Multicentre Growth Reference Study Group. WHO Child Growth Standards. Acta Pædiatrica, 2006; Suppl 450: 76_/85.
9. Technical report)WHO Multicentre Growth Reference Study Group. WHO Child Growth Standards: Length/height-for-age, weight-forage, weight-for-length, weight-for-height and body mass index-for-age: Methods and development. Geneva: World Health Organization; 2006.

This material has been prepared by V. Reddy on behalf of the IFM's Advisory Committee on Child Health and Nutrition, September 2006.