According to researchers in the UK, how much a child's head grows by the time he or she reaches age one may be an indication of a child's intelligence.
The researchers from the University of Southampton, in England say although they do not know exactly what causes some babies to have bigger brains than others, the brain volume a child achieves by the age of one year helps determine later intelligence.
Lead author Catherine Gale, PhD, of the University of Southampton says head growth, especially in infancy may be one of those factors.
Gale and her team studied 633 full-term British babies from the Avon Longitudinal Study of Parents and Children.
They measured with a tape measure the babies' head circumference at birth, one year, four years, and eight years.
The children were given Wechsler Preschool and Primary Scale of Intelligence at the age 4 years old and the Wechsler Intelligence test at 8 years of age and it was found that those with the biggest heads achieved the highest IQ scores.
The researchers suggest that brain growth after infancy, at least in terms of brain volume, is unlikely to compensate for poor growth in the first year of life and did not seem to be as significant.
For the study the researchers also studied the babies' parents; mothers were asked to complete surveys about their parenting style, their older children, and other factors such as breastfeeding and postpartum depression and each mother was given a parenting score based on the survey results.
It was found that babies tended to have higher IQ scores if their parents had more education, had been breastfed for three or more months, and had mothers with high scores on the parenting questionnaire.
This remained the case even after adjustments were made for all those factors, and babies' head growth by age 1 remained tied to IQ scores among the 4- and 8-year-olds.
The researchers say that their findings provide 'additional evidence that infancy is the most important period of postnatal brain growth for determining later intelligence'.
They conclude that the brain volume a child achieves by the age of one year helps determine later intelligence.
Growth in brain volume after infancy may not, they say, compensate for poorer earlier growth.
The research is published in the current edition of Pediatrics.