Monthy growth increments from a longitudinal study of Canadian infants.

Reference data for 1 month increments in weight, recumbent length, and head circumference, at ages 1 to 12 months, have been derived from serial data for 351 full-term Canadian infants. This derivation was achieved by (1) fitting a family of three parameter mathematical models to the data for each infant, (2) using these models to estimate values 1 month apart (3) calculating 1 month increments from the status values of 1 month intervals, (4) obtaining the distributions of these increments, and (5) presenting the percentiles of these increments in tables and in figures. The 1 month increments decreased with age during infancy in each sex, and these increments tended to be more rapid for boys than for girls. It is suggested that these reference data are suitable for the assessment of growth rates in infants born at term in Canada or in the United States. They can be used to assist the early identification of deviations from expected growth rates for individuals and to compare population samples.