Babies who are tiny at birth are less likely to do well in their GCSEs as teenagers, researchers have found.
Small babies may be at a disadvantage
Researchers studied the exam results of 334 16-year-olds who sat GCSE exams in Merseyside, north west England.
They gave a numerical score to each GCSE grade, starting with eight for A* to one for a G grade.
Half the children in the study had weighed 1,500 grams (3.3lbs) or less at birth, compared to a normal birth weight of between 2,500 (5.5lbs) and 3,500 grams (7.7lbs).
The researchers also looked at the results of formal intelligence (IQ) tests, which the children had taken at the age of eight.
And they assessed various influential factors, such as social class, employment and housing status, parental education and income, and number of children in the family.
The results showed that the normal birth weight group scored an average of 36.78 points in their exams.
But the children who had been underweight babies scored an average of just 32.33.
In terms of exam grades, the normal birth weight group scored almost half a grade higher for each subject.
Maths and English
The normal birth weight group achieved significantly better grades for mathematics and statistics and higher grades in general science, English and English Literature.
Both groups achieved similar results for geography and history.
The national average for children achieving five or more subjects at grade C or above in 1997 was 45%.
The normal birth weight group achieved 44%, but the low birth weight group achieved just over 38%.
Children who scored more highly on the IQ test at the age of eight, achieved significantly better GCSE results.
The researchers, led by Professor Peter Pharoah, of the Foundation for the Study of Infant Deaths at the University of Liverpool, say their work suggests that very low birth weight clearly affects subsequent intellectual and academic performance.
They believe this effect may be more important than the social environment or the quality of school education.
Professor Pharoah said the reason why low birth weight should be linked to poor academic achievement was unclear.
It was possible that in some cases children did not receive proper nutrition while in the womb, while in other cases premature birth may have disrupted brain development.
Medical science could take good care of premature babies, he said, but it was very difficult to replicate the type of nutrition provided by a mother in utero.
It was also possible that poor growth, or prematurity were the result of a congenital abnormality which might also have a direct impact on the development of intellect.
"More and more of these children are surviving with improved care but we need to be thinking of what else we need to do to give them the best start in life."
However, Professor Pharoah stressed that many low birth weight babies would go on to be academically successful.
"This is not a simple relationship. There is a chance they won't do quite as well, but an individual can confound all your predictions," he said.
The research is published in the journal Archives of Disease in Childhood.