Data for the CDC Growth Charts included:

physical measurements of stature or length, and weight from infants, children, and adolescents up to 20 years of age.
head circumference measurements from infants and children up to 36 months of age were also used.

The measurement data were obtained from a series of national health examination surveys conducted by NCHS from 1963 to 1994 and from supplemental data sources. These surveys and data sources included:

the National Health Examination Survey (NHES), Cycles II and III
the National Health and Nutrition Examination Survey (NHANES) I, II, and III
U.S. Vital Statistics
Wisconsin Vital Statistics
Missouri Vital Statistics
Fels Longitudinal Study
Pediatric Nutrition Surveillance System

In each of the cross-sectional surveys, a national probability sample of the civilian, non-institutionalized population of the United States was examined. Survey-specific sample weights were applied to the national survey sample data to assure representation of the U.S. population according to age, gender, and racial/ethnic composition at the time the surveys were conducted. Supplemental data sources provided data for birth to 2 months of age. The large sample size in these surveys and the pooling of older data added precision for calculation of the outlying percentile estimates, especially the 3rd and 97th percentiles, to better assess children who are growing at the extremes.

For the first time, nationally representative data were used to construct the growth charts for infants from birth to 36 months of age.

Data used to create the growth charts for children and adolescents 2 to 20 years of age were nationally representative and obtained from 5 national survey data sets.

These data were excluded to avoid an upward shift in the weight-for-age and BMI-for-age curves (Kuczmarski et al., 2000).

The new reference represents the combined growth pattern of breast and formula fed infants in the U.S. About 50 percent of the infants were reported to breastfeed with about 33 percent breastfeeding for 3 months or longer. Because the patterns of growth for exclusively breastfed and formula fed infants differ, caution must be used when interpreting growth of exclusively breastfed infants. Currently, a reference for exclusively breastfed infants is not available. The American Academy of Pediatrics (AAP) recommends exclusively breastfeeding for the first 6 months and continuing for at least 12 months. To better understand the growth patterns of exclusively breastfed infants, 'read more' for a comparison of exclusively breastfed infants to the reference population for the 2000 growth charts.

It is difficult to recommend a growth chart to use for assessing the growth status of VLBW infants because of the significant limitations of the two best options: 1) the VLBW Infant Health and Development Program (IHDP) chart (Guo et al., 1996; Casey et al., 1991; Casey et al., 1990); and 2) the CDC growth chart (Kuczmarski, 2000). The best available VLBW-specific growth chart, the IHDP chart, was developed in 1985, prior to the implementation of current medical and nutritional care protocols that may significantly improve growth, and the CDC growth charts do not include VLBW infants.

Either of these charts is acceptable to use, however users need to consider the following:

1. post-natal age needs to be corrected for gestational age from birth to at least 24 months of age, irrespective of which chart is used (Roche, 1999).

2. the growth of VLBW infants plotted on the CDC charts will be similar to that of VLBW infant plotted on the IHDP growth charts with the possible exception of weight-for-length. Their weight-for-length may show less falling off in growth than is apparent when the VLBW IHDP growth charts are compared to the CDC growth charts (Sherry 2003).

3. the following differences are likely to exist between the growth of VLBW infants and that of non-VLBW infants as depicted in the CDC growth charts (Sherry 2003):

a) VLBW infants usually are and will continue to be smaller in length-for-age and in weight-for-age than the non-VLBW infants. Thus, VLBW infants will fall in the lower percentiles.

b) VLBW infants will exhibit some catch-up growth in length-for-age and head circumference-for-age, however, there will likely be a falling off in weight-for-age and weight-for-length. Thus, they will exhibit an increase in percentiles in length-for-age and in head circumference-for-age and exhibit a decrease in percentiles in weight-for-age and in weight-for-length.

c) VLBW infants are likely to be heavier for their length than non-VLBW infants until they reach 65 cm, at which point they cross over the CDC percentile lines and will become thinner for their length than non-VLBW infants.

4. external VLBW data set comparisons show that with the exception of weight-for-length, the pattern of growth of VLBW infants more closely follows the pattern of the IHDP charts than that of the CDC charts. The VLBW infant pattern of growth in weight-for-length in these external data sets shows that they more closely resemble that of the CDC growth charts. This is particularly apparent when their Z-scores are compared.