Warwick researchers followed more than 92,000 children from infancy to adolescence to explore how their size at birth was associated with early development, and later performance in national school tests.
The large study found that children who were smaller than expected at birth - meaning that they weighed less than most babies of the same sex who were born at the same stage of pregnancy - tended to achieve lower scores in some school subjects, particularly mathematics and reading. The differences were still apparent in adolescence, suggesting that the link between size at birth and academic performance persists well beyond early childhood into mid-teens.
All the children in the study were born at full 'term', between 37 and 41 weeks of pregnancy.
The researchers also looked at when babies were born within the 37-41 week term period, finding that babies born at 37-38 weeks tended to have slightly poorer language and movement skills in early childhood than those born at 39-41 weeks, but the differences had become minimal by the time they started school.
Researcher Xuan Zhao, from the University of Warwick's Department of Psychology, said:
"What surprised us was the contrast between the two patterns: differences linked to being born slightly earlier within the term period largely washed out by age five, while those linked to being smaller than expected were still apparent in school performance at 14-15 years of age."
Professor Siobhan Quenby MBE from the University of Warwick's Medical School, added:
"This study is important because we now know that if your baby is normal size or large for its stage in pregnancy there are no long-term effects of being delivered a few weeks before your due date.
"Not every baby born smaller than expected will experience difficulties. However, the study underlines the importance of monitoring a baby's growth and ensuring that children receive appropriate support as they develop."
Professor Dieter Wolke, Professor of Developmental Psychology and Individual Differences at the University of Warwick, commented:
"For babies born at term, being small for their stage of pregnancy may indicate adverse effects on the brain that affect learning and last into adolescence. However, the long-term effects of being born small may be altered by parenting home stimulation and school support for term born children."
The study was led by researchers from the University of Warwick and the PsychGen Centre at the Norwegian Institute of Public Health, working with other collaborating institutions in Norway. The findings are published in the American Journal of Obstetrics and Gynecology.
