In comparison with the body as a whole the central nervous system grows precociously during prenatal life and the period of infancy.1 About 75 per cent of the bulk of the brain has been established by the conclusion of the first year of life. Injury to the developing brain may manifest itself functionally or structurally. In some instances injury to the brain incurred at birth or during infancy does not make itself obvious until malfunction becomes apparent at a later age. In other instances, however, injury to the brain affects the rate of growth of the cranium. It follows, then, that if the physician has a means of appraising accurately the degree and rate of growth of the head of an infant, he often will be able to discern damage to the central nervous system earlier than otherwise would be possible.
Measurement of the circumference of the head is
BOYD JD. CLINICAL APPRAISAL OF INFANTS' HEAD SIZE. Am J Dis Child. 1945;69(2):71–82. doi:10.1001/archpedi.1945.02020140003001