Information about the growth charts: Key questions around introduction of the new and revised growth charts for Victorian children (CDC 2000 growth charts)

Page content: Why have the CDC growth charts been introduced in Victoria? | What charts are available and what do they measure? | What are the key changes in the new and revised growth charts? | What is Body Mass Index (BMI)? | How to interpret the new BMI percentile charts? | How accurate are the revised charts for tracking growth of exclusively breastfed infants? | How appropriate are the new charts for assessing the growth for different ethnic groups? | What about the growth charts currently under development based on fully breastfed infants? | What reference standard is appropriate in population and clinical research? | References | Download document

Why have the CDC growth charts been introduced in Victoria?

Victoria has been the first Australian state to adopt the recommendation of the NH&MRC “Clinical Practice Guidelines for the Management of Overweight and Obesity in Children and Adolescents” and the Australian Paediatric Endocrine Group and use the 2000 US Centre for Disease Control (CDC) growth charts to assess and monitor the growth and health of Australian children.

The Department of Human Services has included these updated growth charts and new BMI percentile charts in the 2005 editions of the Child Health Record. The growth charts are also freely available in A4 formats for clinical use by health professionals.

What charts are available and what do they measure?

In total there are 12 charts for use in Victoria including:

• Updated weight for age, height for age and head circumference percentile charts for boys and girls aged birth to 36 months,
• Updated weight for age and height for age percentile charts for boys and girls 2-20 years of age,
• New BMI-for age percentile charts have been introduced for the first time for children over the age of two years.

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What are the key changes in the new and revised growth charts?

For many years there have been a number of growth charts in use across Australia. The most common growth charts are based upon the US National Centre for Health Statistics (NCHS) data published in 1997. In 1978 the World Health Organisation adopted this growth reference population for international use. Two of the key limitations of these growth charts were:

• Limitations relating to the infant data, which were collected between 1929 and 1975 by the Fels Institute in the USA. The infants studied were middle class, white and lived in a relatively small part of southwest Ohio. The infants were predominately formula fed which reflected common feeding practices of the time (4)
• There was a disjunction that occurred between 24 and 36 months of age when switching from length to height using the 1977 NCHS growth charts. This meant that when changing from measuring a child’s recumbent length to standing height there appeared to be an upward shift in height that could be misinterpreted as an improvement in linear growth. This ‘improvement’ was actually an artefact of the 1977 charts and occurred in part because recumbent length data from the 1977 charts were obtained from the Fels data set, while height data were obtained from NCHS data. In the new growth charts, there is no longer a disjunction for this age group because both recumbent length and height data were taken from the same child (6).

The revised CDC growth charts have been created from data collected over a 31 year period between 1963 and 1994 within the USA National Health and Nutrition Examination Survey (NHANES) program. The data collected and used to create the new charts are more representative of the entire US population, with the proportion of breast fed infants in the cohort being very similar to that in the general population (4).

A decision was made to exclude data relating to body weight (and therefore body mass index) from the most recent NHANES III study completed in 1994 as it was felt that body weight had become positively skewed due to the increasing trend of overweight and obesity in the US population (4).

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What is Body Mass Index (BMI)?

BMI is a weight-to-height ratio that is significantly associated with body fatness in childhood and adolescence. The BMI has been used extensively over many years to assess overweight and obesity in adults. The NHMRC now recommends that the BMI can be used as a reasonable, easily determined surrogate measure for adiposity for children over the age of 2 years (3).

BMI is calculated using weight and height measurements, then used to compare a child’s weight relative to height with other children of the same age and gender, using the BMI percentile charts.

The following equation can be used to determine BMI

BMI= Weight (kg) / [height (m) x height (m)]

How to interpret the new BMI percentile charts?

A recent study has shown that parents do not often recognise overweight in themselves or their children (5). Health professionals may also not recognise underweight, on casual examination often assuming that the child is younger than they actually are (1).

For the first time in Victoria, new CDC BMI percentile charts are available for use in children over the age of two to assess overweight and obesity. BMI changes with age and with gender. An absolute BMI calculation for a child or for an adolescent below the age 18 years must be evaluated against age and gender reference standards (3).

The NHMRC, “ Clinical Practice Guidelines for the Management of Overweight and Obesity in Children and Adolescents” has recommended the use of the latest CDC 2000 BMI percentile charts, with the 85th percentile and above indicative of overweight and the 95th percentile and above indicative of obesity (3). These percentile cut offs should however be used as reference or a guide.

It is important to note that discussion of children’s weight and associated food and activity patterns can be a sensitive issue. Carers should understand that the growth chart is a screening tool. It is intended to be a guide of when to take small steps to make changes and when to seek further guidance from a doctor or an Accredited Practising Dietitian (APD).

A range of nutrition tip and fact sheets have been developed to help with issues related to the eating habits of families and children (0-8 years). The tip sheets are available to distribute to parents and carers and can be downloaded free of charge from the Public Health Nutrition website.

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How accurate are the revised charts for tracking growth of exclusively breastfed infants?

The revised charts are derived from a mix of infants who were exclusively breast fed and formula fed. Exclusively breast fed babies may grow at a slightly lower rate than the reference, particularly in the first 4-6 months of age. However if the charts are used as a reference (and not as a standard that must be met) the difference is not important (approximating a Z score of –0.5) (1).

How appropriate are the new charts for assessing the growth for different ethnic groups?

As nutritional status improves around the world the differences in birth weight between racial groups is lessoning. Mean birth weights in China and Vietnam are now the same as in Australia and other developed countries. Genetic differences appear to be less important than nutritional status in determining growth rates and ultimate body size. There is more difference between children from well-nourished higher socio-economic groups and disadvantaged children within the same country than there is between the higher socioeconomic groups in different countries (1).

The data used to develop the CDC growth charts were collected to ensure it was representative of the US population according to age, sex and racial/ethnic composition at the time the surveys were conducted from 1963 to 1994. The CDC promotes the new growth charts for all racial and ethnic groups (6).

What about the growth charts currently under development based on fully breastfed infants?

In mid 2006 it is anticipated that the World Health Organisation (WHO) will release new growth curves for infants and children aged from birth to five years. This is the result of the WHO Multicentre Growth Reference Study (MGRS) which was undertaken between 1997 and 2003. Data was collected from about 8500 children from widely differing ethnic backgrounds and cultural settings (Brazil, Ghana, India, Norway, Oman and USA). The new growth curves are expected to provide a single international reference that represents the best description of physiological growth for all children under five years of age and to establish the breastfed infant as the normative model for growth and development.

What reference standard is appropriate in population and clinical research?

In 1999 an expert committee, on behalf of the International Obesity Task Force, recommended that BMI be used to assess adiposity in children and adolescents. Following on from the recommendations, Cole et.al (2000) developed tables for categorising overweight and obesity in population and clinical research. The tables allow international comparison of the prevalence of overweight and obesity, as well as assessment of trends within populations. These tables are not however suitable for use in clinical practice. For clinical practice, the use of a BMI–for-age chart is more suitable since an individual can be described in terms of a percentile-for example, above the 85th percentile-and their progress plotted on a chart that forms part of the clinical record (2).

References

1. Binns,C, Why Measure Anthropometric Parameters?, Food Chain, Strategic Inter-governmental Nutrition Alliance, Issue No17, August 2005.
2. Dietary Guidelines for Children and Adolescents in Australia. A guide to healthy eating, National Health & Medical Research Council, April 2003.
3. Clinical Practice Guidelines for the Management of Overweight and Obesity in Children and Adolescents, National Health & Medical Research Council, 18 September 2003.
4. Davies,P, Growth Assessment, Food Chain, Strategic Inter-governmental Nutrition Alliance, Issue No17, August 2005.
5. Jeffery A, Voss L, Metcalf B, Alba S, Wilkin T. Parents awareness of overweight in themselves and their children: cross sectional study within a cohort. BMJ 2005; 330:23-24.
6. Polhamus,B, Thompson D et al. Overview of the CDC Growth Charts. Medscape webbmd http://www.medscape.com/viewprogram/2660_pnt
   

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The document below is a printable version of the information on this page.

Key questions around introduction of the new and revised growth charts for Victorian children (CDC 2000 growth charts) (34kb, pdf)

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