Babies born a week early are more prone to develop a series of learning difficulties such as autism and deafness, research suggested today.
The study of more than 400,000 British children showed that those born at 39 weeks were more likely to need help at school compared with babies who spent 40 weeks in the womb.
The results "suggest that deliveries should ideally wait until 40 weeks of gestation because even a baby born at 39 weeks...has an increased risk of Special Educational Needs (SEN) compared with a baby born a week later", the experts concluded.
Around a third of UK births take place at 37 to 39 weeks, a rate that has increased in recent years as more mothers choose earlier deliveries for non-medical reasons.
The British study, which was funded by the NHS, looked at the school and hospital records of nearly 408,000 schoolchildren across Scotland.
Nearly 18,000 of the children were classed as having an SEN - such as dyslexia or autism, or a physical difficulty such as deafness or poor vision.
A total of 8.4% of the children who were born pre-term were found to have a learning difficulty, compared with just 4.7% for those born at-term.
The study also found that compared to children born at 40 weeks, children born between 37 and 39 weeks were 1.16 times as likely to have an SEN.
This tendency increased the earlier the delivery, rising to 1.53 times for children born at 33 to 36 weeks, and 2.66 times for those born between 28 and 32 weeks.
Babies born between 24 and 27 weeks were found to be 6.92 times as likely to have potential learning difficulties.
"These findings, which are likely to be accurate because of the large size of the study and its design, have important implications for the timing of elective delivery," the study said.
Public health professor Jill Pell from Glasgow University told the Daily Mail the chances of any one baby being affected were very low.
But she added: "It is important from a public health point of view as so many infants are born pre-term.
"A third of deliveries take place at 37 to 39 weeks. Across the country, that is an awful lot of extra cases of special educational needs due to slightly early deliveries."