Head growth in fetal life and infancy is associated with later intelligence
Moreover, catch-up increases do 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," the study team writes in the journal Pediatrics. "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."
Several 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.
For their study, Dr. Catharine R. Gale, of the University of Southampton, UK, and colleagues examined the effect of head growth in fetal life, infancy, and childhood on brain power at the ages of 4 and 8 years. Included in the study were 633 term children who had their head circumference measured at birth and at regular intervals thereafter.
By age 1, mean head circumference increased from 34.9 cm at birth to 46.6 cm. Head growth after infancy was slower. Mean head circumference increased to 50.9 cm by 4 years and to 53.4 cm by 8 years.
Average full-scale IQ was 106.3 at 4 years and 105.6 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.
Critical periods of brain growth and cognitive function in children
The Influence of Head Growth in Fetal Life, Infancy, and Childhood on Intelligence at the Ages of 4 and 8 Years