The growth of the head in fetal life and infancy is associated with the level of intelligence later. Moreover, the catch-up later on may not appear to compensate for poor early growth. Brain growth in early life may be important in determining not only the level of peak cognitive function attained but also whether such function is preserved in old age. Older people with a larger head circumference tend to perform better on tests of cognitive function and may have reduced risks of cognitive decline and of Alzheimer's disease. Previous studies in children have shown that those with larger brains, measured with imaging studies or as head circumference, tend to score higher on tests of cognitive function. Similar associations have been found in adults. Researchers from the University of Southampton, UK, examined the effect of head growth in fetal life, infancy, and childhood on brain power at the ages of 4 and 8 years. The study Included 633 term children who had their head circumference measured at birth and at regular intervals thereafter. By the age of 1 year, mean head circumference increased from 35 cm at birth to nearly 47 cm. Head growth after infancy was slower. Mean head circumference increased to 51 cm by 4 years and to 53 cm by 8 years. Average full-scale IQ was 106 at 4 years and 106 at 8 years. The investigators report that only prenatal growth and growth during infancy were associated with later IQ. At 4 years, after adjusting for parental factors, there was an average increase in full-scale IQ of 2.41 points for each 1 standard deviation increase in head circumference at birth and 1.97 points for each 1-SD increase in head growth during infancy. This was conditional on head size at birth. Head circumference at birth was no longer associated with IQ at 8 years. However, head growth during infancy remained significantly predictive, with full-scale IQ increasing an average of 1.56 points for each 1-SD increase in head growth.
Pediatrics,
October 2006