Premature babies can need extra healthcare through childhood
Babies born prematurely may suffer the health consequences all the way through to adulthood, a major study suggests.
An analysis of nearly 1.2m births in Norway revealed those born early were more likely to die as children and less likely to reproduce as adults.
They also had a poorer educational record, the Journal of the American Medical Association study found.
However, experts stressed researchers followed children born decades ago - prior to many advances.
They said the overall risk of early death was low.
It has long been known that premature babies - categorised in this study as those born before 37 weeks - may suffer various medical and developmental problems compared to their full-term counterparts.
But few studies have looked at the long-term consequences for the premature.
This research, carried out by US and Norwegian researchers, involved 60,354 premature births.
For those born very early - between 22 and 27 weeks - mortality rates up to the age of six were more than five times higher in boys and almost ten times higher among girls.
In late childhood, up to the age of 13, these boys were more than seven times more likely to die than full-term babies. There were however no deaths among the girls.
For those born between 28 and 32 weeks, boys were about 2.5 times more likely to die, but again there was no impact on the girls. The overall chance of death for all the groups was still low, around the 1% mark.
Nonetheless, their lives apparently continued to be affected by their time of birth. Taken as a whole, they were less likely to complete secondary school, and less likely to go on to have children themselves.
Only 14% of men and 25% of women had their own child, compared with 50% of men and 68% of women who were born at term.
But "it is not absolutely a cause for alarm that if your child is born prematurely, something terrible is going to happen to it", said Dr Geeta Swamy of Duke University Medical Center, who carried out the research.
The reasons for premature birth are not properly understood, but some of the factors which may be involved - such as poor diet and lifestyle - may themselves impact independently upon the health of the child.
In addition, observers noted that the babies were born as far back as 1967.
"These outcomes are all from babies who didn't benefit from the most modern respirators, the most modern technology, the most modern treatments," said Dr Alan Fleischman, medical director of a US premature birth charity, March of Dimes.
But the head of the UK leading baby charities, Tommy's, said the findings highlighted that "premature birth is a bigger problem than people think".
"The UK has the highest rate of premature birth in all of Western Europe, and is known to greatly increase a child's risk of serious long term health problems," said Jane Brewin.
"These findings support the argument for further research to be done into finding the causes of premature birth, so that more babies can be given the best chance of being born healthy."