In the 1970's multi-purpose growth charts were developed by the Centers for Disease Control and Prevention (CDC), National Center for Health Statistics (NCHS) to evaluate and monitor the growth of infants and children in the United States. Although they have been used for more than 20 years, the charts were based on samples of children that did not represent the U.S. population. A major concern was the use of data collected on infants (birth to 36 months) in the Fels Longitudinal Study. From 1929 to 1975 data were collected from a single longitudinal study of primarily formula-fed, white middle-class infants in a limited geographic area of southwestern Ohio.
In 1985 the NCHS began a process to revise the 1977 NCHS charts, using improved statistical procedures and incorporating additional national survey data. The revised growth charts were developed to describe the size and growth of children in the United States. They are based primarily on physical measurements taken as part of a series of national health examination surveys conducted by NCHS from 1963 to 1994. These surveys included Cycles II and III of the National Health Examination Survey (NHES II and III) and three National Health and Nutrition Examination Surveys (NHANES I, NHANES II, and NHANES III).
Major Features of the Revised Growth Charts
The
most important features of the revised growth charts include:
Specifically, the weight-for-age percentile distributions are now continuous between the infant and the older child charts at 24 - 36 months. The length-for-age to stature-for-age, and the weight-for-length to weight-for-stature curves are parallel in the overlapping ages of 24 - 36 months, but have been adjusted slightly to account for the fact that recumbent length should be greater than stature for any individual. Below age 24 months, the revised weight-for-age curves are generally higher than in the 1977 charts. This will result in more frequently classifying infants as underweight.
BMI-for-age Growth Curves
The most prominent
change to the complement of growth charts for older children and adolescents is
the addition of the BMI-for-age growth curves. The BMI-for-age charts were
developed with national survey data (1963 -1994) excluding data from the 1988 -
1994 NHANES III survey for children older than 6 years because an increase in
body weight and BMI occurred between NHANES III and previous national surveys.
Without this exclusion, the 85th and 95th percentile curves would have been
higher, and fewer children and adolescents would have been classified at risk
or overweight. Therefore, the BMI-for-age growth curves do not represent the
current population of children over 6 years of age.
The sex-specific BMI-for-age charts for ages 2 to 20 years replace
the 1977 NCHS weight-for-statures charts that were limited to prepubescent boys
under 11.5 years of age and statures less than 145 cm, and to prepubescent
girls under 19.0 years of age and statures less than 137 cm. BMI-for-age may be
used to identify children and adolescents at the upper end of the distribution
who are either overweight (
95th
percentile) or at risk for overweight ( 85th and <
95th percentile). The
formulas for
determining BMI are available on the CDC website.
Breast- and Formula-Fed Infants
The national
survey data better represent the combined size and growth patterns of in the
general U.S. population (1971 to 1994). Over the past two decades in the United
States, approximately one-half of all infants were reported to have been ever
breast-fed and approximately one-third were breast-fed for 3 months or more.
Therefore, compared with the 1977 NCHS growth charts, the nationally
representative data on which the revised infant growth charts are based will
better represent the combined growth patterns of breast-fed and formula-fed
infants in the U.S. population.
With regard to differences in the growth of breast- or formula-fed infants, other research efforts are currently ongoing to address this issue. A Working Group of the World Health Organization (WHO) is collecting data at seven international study centers to develop a new set of international growth charts for infants and preschoolers through age 5 years. These charts will be based on the growth of exclusively or predominately breast-fed infants. The basic assumption is that infants from healthy populations, following the current WHO feeding recommendations, are growing optimally. The WHO multi-center growth reference study should be completed in 2002.
Special Groups
Although there are differences in
size and growth among the major racial/ethnic groups in the U.S., these appear
to be small and inconsistent. Therefore, the revised growth charts include all
infants and children in the United States whatever their race or ethnicity.
Because the growth patterns of preterm, VLBW infants are considerably different
from those of higher birth weight term infants and specialized growth charts
exist to track the growth of VLBW infants, data for VLBW (<1500 gm) infants
were excluded from the revised infant growth charts.
Versions of the Growth Charts
Three different
versions of the charts are available on www.cdc.gov/growthcharts. The first set
contains all nine smoothed percentile lines (3rd, 5th, 10th, 25th, 50th, 75th,
90th, 95th, 97th), and the second and third sets contain seven smoothed
percentile lines each. The second set contains the 5th and 95th percentile
lines and the third set contains the 3rd and 97th percentile lines at the
extremes of the distribution. In addition, the charts for weight-for-stature
and BMI-for-age contain the 85th percentile. In all the growth charts, age is
truncated to the nearest full month, for example, 1 month (1.0-1.9 mo), 11
months (11.0 to 11.9 mo), 23 months (23.0-23.9 mo), and so forth.
The three sets of charts are provided to meet the needs of various users. Set 1 shows all of the major percentile curves, but may have limitations when the curves are close together, especially at the youngest ages. Most users in the United States may wish to use the format shown in set 2 for the majority of routine clinical applications. Pediatric endocrinologists and others dealing with special populations, such as children with failure to thrive, may wish to use the format in set 3.
Since nurses are often responsible for measuring growth in children, it is essential that they have an understanding of the revised growth charts. Several important differences exist between the 1977 and the revised charts with significant implications for classifying children as underweight or overweight. Nurse need to become familiar with determining BMI which only requires information about the child's weight and height. With the increasing number of children who are overweight in the U.S., the BMI charts will increasingly become a critical component of children's physical assessment.
March 15, 2002