Reference data for head circumference and 1-month increments from 1 to 12 months of age.

Serial head circumference measurements in 462 participants in the Fels Longitudinal Study were used to develop reference data for ages 1 to 12 months. We used a three-parameter mathematical function to model the serial head circumference data for each individual and estimated head circumference at 1-month intervals. Reference data for selected percentiles of head circumference status and 1-month increments were calculated from the estimated head circumferences. These reference data are presented in tables and charts for use in testing hypotheses about group differences or to monitor changes within individuals.