Monthly growth status from a longitudinal study of Canadian infants.

Reference data for weight, recumbent length and head circumference at 1-month intervals from 1 through 18 months have been developed from measurements of 351 healthy infants born at term in Montreal or Toronto. Each infant was measured serially from 1 to 18 months. A 3-parameter mathematical model was fitted to the serial data for each infant. The model fitted the serial data well for almost all the infants as evaluated by the residual mean square errors. Subsequently, values were estimated for each month of age from 1 through 18 months for each infant. These estimated values allowed the development of reference data that have been presented in tables and in graphs.