Twenty-eight of 100 children followed because of severe illness in early infancy were found to have head circumferences 2 standard deviations or more below the mean when examined at age 1 year. Sixteen had diagnoses not ordinarily expected to result in mental retardation; 12 had diagnoses implying possible injury to the central nervous system (CNS). Although mean head circumference was similar for these two groups, incidence of mental retardation was higher in children with CNS-associated diagnoses (75% as opposed to 31%). Generally, the most retarded had the smallest heads. The pattern of head growth over the first year of life was more meaningful than a single measurement at age 1 year. The 28 microcephalic babies were somewhat undergrown with respect to height and weight. Half of these babies were developing normally or were only mildly delayed; caution should be exercised in prematurely attributing severe mental retardation to all infants with measurement microcephaly.
Avery GB, Meneses L, Lodge A. The Clinical Significance of "Measurement Microcephaly". Am J Dis Child. 1972;123(3):214-217. doi:10.1001/archpedi.1972.02110090084008