Methods
Healthy, appropriate-for-gestational-age, singleton, white infants weighing less than or equal to 2500 g at birth and with normal development at 18 months of age were included in this study. Serial measurements of head circumference (corrected for gestational age) from 450 eligible infants were compared with reference data for head circumference.

Results
Longitudinal measurements of head circumference for infants weighing more than 1000 g at birth were similar to reference data for term infants. Head measurements for infants weighing less than or equal to 1000 g at birth were notably smaller than the measurements in the reference data. A cubic spline curve drawn through the head circumference measurements between birth and age 18 months (corrected for gestational age) for infants weighing less than or equal to 1000 g at birth was significantly (P<.001) below the curve for infants weighing more than 1000 g at birth. At age 18 months, the mean difference in head circumference between the group weighing less than or equal to 1000 g at birth and the weights in the reference data was 1.6 cm (P<.01). (Data were analyzed with Wilcoxon's signed rank test.)

Conclusions
These data show that head circumference grids are appropriate for observing head growth in infants with a birth weight more than 1000 g. However, head circumference growth for normal infants with birth weight less than or equal to 1000 g does not "catch up" with that of larger premature infants or term infants.

(Arch Pediatr Adolesc Med. 1995;149:1358-1361)