Growth standards for infants and children: a cross-sectional study.

Measurements of height and weight were collected on 1,233 Black and white infants and children attending a Child Health Clinic in Washtenaw County, Michigan. Polynomial curves were fitted to each race and sex group and, from these, estimates were made of the 3rd, 50th, and 97th percentiles for height and weight. Blacks tended to be lighter and shorter than whites in early infancy. In the second year of life, Blacks tended to exceed whites in height and weight achievement. For infants and children in the 97th percentile this change in status occurred earlier. The differences in weight and height achievement were statistically significant in the two race groups, but not between sexes. The percentile estimates differed significantly from the percentiles of local as well as the "Iowa," "Harvard," and "Tanner" (United Kingdom) standards. Differences in the racial and environmental background of the clinic population and the samples used in the development of the national standards probably accounts for the variations in the percentile estimates. It is concluded that race- and sex-specific standards are required before growth achievements in infants and children can be properly evaluated.