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Percentiles are the most commonly used clinical indicator to assess the size and growth patterns of individual children in the United States. Percentiles rank the position of an individual by indicating what percent of the reference population the individual would equal or exceed. For example, on the weight-for-age growth charts, a 5-year-old girl whose weight is at the 25th percentile, weighs the same or more than 25 percent of the reference population of 5-year-old girls, and weighs less than 75 percent of the 5-year-old girls in the reference population.

A z-score is the deviation of the value for an individual from the mean value of the reference population divided by the standard deviation for the reference population. Because z-scores have a direct relationship with percentiles, a conversion can occur in either direction using a standard normal distribution table. Therefore, for every z-score there is a corresponding percentile and vice versa.

If you are concerned about your child’s growth, talk with your child’s health care provider.

In the United States, the WHO growth standard charts are recommended to use with both breastfed and formula fed infants and children from birth to 2 years of age (obÌåÓý, 2010). The WHO growth charts reflect growth patterns among children who were predominantly breastfed for at least 4 months and still breastfeeding at 12 months. These charts describe the growth of healthy children living in well-supported environments in sites in six countries throughout the world including the United States. The WHO growth charts show how infants and children should grow rather than simply how they do grow in a certain time and place and are therefore recommended for all infants (Dewey, 2004; WHO Multicentre Growth Reference Study Group, 2006).

The WHO growth charts establish the growth of the breastfed infant as the norm for growth. Healthy breastfed infants typically put on weight more slowly than formula fed infants in the first year of life (Dewey, 1998). Formula fed infants gain weight more rapidly after about 3 months of age. Differences in weight patterns continue even after complementary foods are introduced (Dewey, 1998).

There are no plans to update the growth charts.

The 2000 obÌåÓý growth charts were created using a reference population from national surveys from 1963 to 1980 for most children and adolescents – before the increase in obesity prevalence. They serve as a “ruler” to compare children today with a historical reference. Because of the increase in average childhood BMI over time, updating the charts with newer data would result in a shift in the percentiles. Specifically, the 95th percentile, the cut point for obesity, would shift upward. Using a new 95th percentile to define obesity would lead to some children being below the 95th percentile who were above using the 2000 charts. As an example, during 2017-March 2020, 19.7% of US children and adolescents were above the 95th percentile of the 2000 obÌåÓý BMI-for-age growth charts and had obesity. If the charts were updated to include only these children, 5%, not 19.7%, would be above the 95th percentile. This would lead to two problems for surveillance of child growth and obesity. First, this new 5% of children would have much higher BMI values than the 5% of children in the original 2000 growth chart reference population who were over the 95th percentile. The health implications of these higher BMI values would require new research and definitions. Second, no meaningful point of reference would be available if the growth charts were continuously updated to change the location of the 95th percentile according to the most recent data. For example, the increases in obesity over the past few decades would not have been identified if the point of reference was changed from the original reference data.

Instructions for Using the Coefficients for the 1977 NCHS Growth Charts

Each percentile curve on each growth chart is defined by a unique group of coefficients.

Coefficients for selected percentile lines [TXT – 21 KB]

The coefficients are in scientific notation (for example, 0.240000D 02 is really 24.0000). The digits after the letter D indicate how many positions the decimal point should be moved to the right or left. A negative number indicates the decimal point should be moved to the left

(e.g., 0.2400000D-02 is really .00240000).

In the table, the first column is the x-axis value and the next four columns refer to the coefficients needed to define the y-axis value on the growth curve using the third order polynomial spline equations which define the curves. The last 4 columns (sex, age, percentile, chart) determine which curve is being defined:

Sex

M=male
F=female

Age codes

1=0-36 moths
2=2-18 years
3=2-10.0 years
4=2-11.5 years

Percentile

5=5th
10=10th
25=25th
50=50th
75=75th
90=90th
95=95th

Chart codes

1=length-for-age
2=weight-for-age
3=weight-for-length
4=head circumference-for-age
5=stature-for-age
6=weight-for-stature

The first three lines define the 5th percentile curve of length for age for males 0-36 months of age. The first value on the line refers to the x-axis variable (in this case, age in months). In the example, the first line has 0.0, the second has 9.0, and the third has 24.0. This means that you should use the first line’s values for ages 0-8 months, the second line for ages 9-23 months, and the third line for ages 24-36 months to find the 5th percentile value for length for age of males 0-36 months.

Each of the four other values refers to the constants for the polynomial equation

Y = constant + B(1)*X + B(2)*X**2 + B(3)*X**3.

For example, if you wanted to know the fifth percentile for length for an 18-month old male, you would use the constants defined on the second line. It would be defined as:

Y = 68.0368 + 1.33232*(18-9) – .0397275*(18-9)**2 +

0.000958204*(18-9)**3

If you wanted the 5th percentile value for length for a 28-month-old male you would use the coefficients on the third line. The X in the equation is age minus the value in the first column, here it is 18-9. This principle may be applied to each percentile curve for each chart. Remember that only the seven selected percentiles are calculated and not any others.

For example, there are no definitions for the 15th percentile or the 3rd percentile. Remember also that the x-axis is always age in months or height in centimeters, depending on the chart being used. No other values should be used in the equations.

Centers for Disease Control and Prevention. Use of the World Health Organization and obÌåÓý growth charts for children aged 0-59 months in the United States. MMWR Recomm Rep. 2010;59(RR-9);1-15. Accessed November 26, 2012.

Dewey KG, Cohen RJ, Nommsen-Rivers LA, Heinig MJ, for the WHO Multicenter Growth Reference Study Group. Implementation for the WHO Multicentre Growth Reference Study in the United States. Food Nutr Bull. 2004;25(suppl1):S84-S89.

WHO Multicentre Growth Reference Study Group. Assessment of differences in linear growth among populations in the WHO Multicentre Growth Reference Study. Acta Paediatr Suppl. 2006;450:56-65.

Dewey KG. Growth characteristics of breastfed compared to formula-fed infants. Biol Neonate. 1998;74(2):94-105.

Ehrenkranz RA, Younes N, Lemons JA, Fanaroff AA, Donovan EF, Wright LL, Katsikiotis V, Tyson JE, Oh W, Shankaran S, Bauer CR, Korones SB, Stoll BJ, Stevenson DK, Papile L. Longitudinal growth of hospitalized very low birth weight infants. Pediatrics. 1999;104:280-289.

Guo SS, Wholihan K, Roche AF, Chumlea WC, Casey PH. Weight-for-length reference data for preterm, low birth weight infants. Arch Pediatr Adolesc Med. 1996;150:964-970.

Guo SS, Roche AF, Chumlea WC, Casey PH, Moore WM. Growth in weight, recumbent length, and head circumference for preterm low-birthweight infants during the first three years of life using gestation-adjusted ages. Early Hum Dev. 1997;47:305-325.

Roche AF, Guo SS, Wholihan K, Casey PH. Reference data for head circumference-for-length in preterm low-birth-weight infants. Arch Pediatr Adolesc Med. 1997;151:50-57.

The WHO standards establish growth of the breastfed infant as the norm for growth. Breastfeeding is the recommended standard for infant feeding. The WHO charts reflect growth patterns among children who were predominantly breastfed for at least 4 months and still breastfeeding at 12 months.

The WHO standards provide a better description of physiological growth in infancy. Clinicians often use the obÌåÓý growth charts as standards on how young children should grow. However the obÌåÓý growth charts are references; they identify how typical children in the US did grow during a specific time period. Typical growth patterns may not be ideal growth patterns. The WHO growth charts are standards; they identify how children should grow when provided optimal conditions.

The WHO standards are based on a high-quality study designed explicitly for creating growth charts. The WHO standards were constructed using longitudinal length and weight data measured at frequent intervals. For the obÌåÓý growth charts, weight data were not available between birth and 3 months of age and the sample sizes were small for sex and age groups during the first 6 months of age.

The obÌåÓý growth charts can be used continuously from ages 2-19. In contrast the WHO growth charts only provide information on children up to 5 years of age.

For children 2-5 years, the methods used to create the obÌåÓý growth charts and the WHO growth charts are similar.

In the US, the prevalence of obesity and severe obesity has increased over the last 40 years and in 2017-2018 more than 4.5 million children and adolescents had severe obesity. The 2000 obÌåÓý (Centers for Disease Control and Prevention) BMI (body mass index)-for-age growth charts do not extend to BMI values high enough for use in children with extremely high BMIs and those with severe obesity. More specifically, the 2000 growth charts have an upper limit of the 97th percentile based on reference data from 1963 to 1980 for most children and adolescents, a period when the prevalence of obesity was lower than today, and data were sparse above this level. Although percentiles above the 97th can be extrapolated beyond the data, the charts provide no information about actual growth patterns above the 97th percentile.

obÌåÓý developed a specialized growth chart tool by adding extended reference curves or percentiles to monitor very high BMI values in children and adolescents. These extended curves are based on additional data for children and adolescents with obesity from 1988 to 2016, increasing the data available in the reference population for children and adolescents above the 95th percentile. Unlike other options for monitoring growth in children with very high BMI values that use theoretical or statistical extrapolations, the obÌåÓý extended BMI-for-age growth charts are based on actual data from nationally representative samples. Pediatric health care providers and researchers can track a child’s trajectory against these new curves that reflect measurements of real children with obesity.

For most children and adolescents, the 2000 obÌåÓý BMI-for-age growth charts remain the most appropriate tool to assess growth and weight status.

The Extended obÌåÓý BMI-for-age growth charts provide an additional and specialized tool for clinicians and researchers to monitor BMI in children and adolescents with very high BMI. They do not replace the 2000 obÌåÓý BMI-for-age growth charts. Instead, they are an extension of the existing curves to be used by those needing to track very high BMIs.

The 2000 obÌåÓý BMI-for-age growth charts should be used for children at or below the 95th percentile. The extended obÌåÓý BMI-for-age growth charts can be used for children above the 95th percentile and are specially designed for children with very high BMI values because these children can be harder to track on the 2000 BMI-for-age growth charts. In most cases, use of the 2000 obÌåÓý and the extended charts should be seamless.

In many pediatric clinics, percentile and z score calculations are incorporated into the electronic health record (EHR). If the EHR has incorporated the extended method for calculating percentiles and z scores above the 95th percentile, then these will be the default percentiles and z scores reported for children above the 95th percentile and no decision about what chart to use is required. Data tables, computer programs, and instructions for calculating percentiles and z scores are available at SAS Program ( ages 0 to < 20 years ) | Resources | Growth Chart Training | Nutrition | DNPAO | obÌåÓý to help with EHR integration.

PDF files are available for download of the 2000 obÌåÓý BMI-for-age growth charts and Extended obÌåÓý BMI-for-age growth charts. The 2000 obÌåÓý BMI-for-age growth charts can be used to plot BMI up to 37 kg/m². Two versions of the Extended obÌåÓý BMI-for-age growth charts are available and show the existing 5th through 95th percentiles, which are identical to the 2000 obÌåÓý BMI-for-age growth charts. Both the percentile and z score versions of the Extended growth charts allow plotting BMI up to 60 kg/m². Above the 95th percentile, the percentile version of the growth chart provides reference curves up to the 99.99^th percentile, while the z score version provides reference curves up to a z score of 5. Note that percentile and z score values are interchangeable and are just expressed on different scales. Both the percentile and z score values give an indication of how far away a child’s BMI is from the median age- and sex-specific BMI value (50th percentile which is equivalent to a z score of 0).

The BMI-for-age growth charts allow comparison of a child’s BMI to a reference population, similar to using and interpreting other growth charts such as weight-for-age and height-for-age. Percentiles and z scores based on the reference population provide metrics for monitoring change in BMI over time and for setting threshold values for overweight and obesity. For most children, the reference for the obÌåÓý BMI-for-age growth charts came from a nationally representative sample of children aged 2–19 years during 1963-1980, a period before recent increases in childhood obesity prevalence.

The 2000 obÌåÓý BMI-for-age curves do not extend beyond the 97th percentile because there were too few children in the reference population with very high BMI values existed to create percentile curves using real data. Curves above the 97th percentile in the 2000 obÌåÓý BMI-for-age charts, however, can be mathematically created or extrapolated for convenience, such as percentages of the 95th percentile. In the extended charts, the newly added percentiles above the 95th percentile are based on nationally representative data for children with obesity from the growth chart reference population and additional data from 1988 to 2016. The extended z scores associated with these new percentiles accurately reflect patterns among real children at extremely high BMI values.

With very high BMI values above the extended 99th percentile, the z score may be an easier number for clinicians, patients, and families to understand. For example, the value of z score=1 is nearly equivalent to the 85th percentile—the threshold for overweight status. A z score of 4 is equivalent to the extended 99.9th percentile, but z scores of 4 and 1 may be easier to convey to patients and families with extended 99.9th and 85th percentiles.

The Extended obÌåÓý BMI-for-age charts are based on data from U.S. children in the National Health and Nutrition Examination Survey. Percentage of the 95th percentile is not based on data on actual children but is a statistical extrapolation. Because 120% of the 95th percentile is the definition of severe obesity, this line is included on the extended BMI-for-age growth charts images.

In addition, the extended BMI-for-age percentiles are an extension of the 2000 obÌåÓý BMI-for-age growth charts so they can be used together seamlessly, unlike the percentage of the 95th percentile.

See the report on alternative BMI metrics for more details on the differences between these metrics.

No. The Extended obÌåÓý BMI-for-age growth charts are an extension of the 2000 obÌåÓý BMI-for-age growth charts. The percentiles up to the 95th percentile (the threshold for obesity) remain unchanged. Consequently, the definitions of overweight and obesity are unchanged. The current threshold for severe obesity (120% of the 95th percentile) is shown as a separate curve on the Extended obÌåÓý BMI-for-age growth chart PDFs.

Data tables, computer programs, and instructions for calculating percentiles and z scores are available at SAS Program ( ages 0 to < 20 years ) | Resources | Growth Chart Training | Nutrition | DNPAO | obÌåÓý to help with EHR integration.