Forty per cent of very premature babies have significant learning disabilities, a BBC Panorama report is set to reveal.
The study followed hundreds of premature babies
The programme has had exclusive access to the unpublished Epicure study, the largest study of its kind.
The study followed 1,200 babies born alive at less than 26 weeks gestation in Britain and Ireland in 1995, just over 300 of whom survived to go home.
Its authors are divided over whether such results mean doctors should continue to help these babies survive.
The findings raise the issue of how far doctors should go to resuscitate babies born at the limits of viability at less than 25 weeks gestation.
A normal pregnancy lasts for around 40 weeks.
The study showed that 4,004 babies were born in Britain between 20 and 25 weeks gestation in 1995.
Just over 1,200 were born alive and 811 were admitted to a neonatal intensive care unit. Of these 314 survived to go home.
The first phase of the study revealed at two and a half years old 50% of those studied had some form of disability.
In a quarter of the children severe disabilities were identified, including cerebral palsy, blindness, deafness and arrested development.
Researchers have now tested the children again at the age of six for IQ levels, attention issues, language abilities and their ability to understand problems.
The latest results show that 40% of the surviving children had moderate to severe problems in cognitive development at the age of six, compared to 2% of a control group of their classmates.
It also found that among those born earliest - at 23 to 25 weeks - boys are twice as likely to have cognitive problems in later life than girls.
In 2002 Dutch neonatologists issued a statement which explained that they do not treat babies born at less than 25 weeks gestation, except in very exceptional cases.
Panorama says that the neonatologists it spoke to in the UK said they would not rule out the idea of being much more selective about babies born on the cusp of viability, but they said they could not accept imposing arbitrary limits based on gestational age.
Professor Neil Marlow of the Queens Medical Centre in Nottingham, who is one of the co-authors of the Epicure study, said: "I do ... [feel justified in attempting to save the lives of babies born on the margins of viability] ...
"And I justify it on the grounds of some wonderful outcomes that one sees and the knowledge that over time we can envisage ways in which we can improve those outcomes."
'Turn off the machine'
But Professor Kate Costeloe, Prof of Paediatrics, Queen Mary, University of London, who also worked on the study said: "I would hope that people understand that being born early is a very, very serious business, that survival is not high, and that should children survive, their likelihood of having life-long problems - particularly in respect of learning is high.
"At 23, 24 weeks I have sometimes thought that if these outcomes are as good as they can be, should we be doing this."
Bright Asamany, born at 24 weeks, is one of the most severely disabled of all the children who were born in 1995.
In this latest study he is described as "functioning at an extremely low level in all areas of development." He was classified as having severe physical and learning disabilities.
Some weeks after Bright's birth, a scan revealed that he had suffered a brain haemorrhage. He now has severe cerebral palsy and severe epilepsy.
He is entirely dependent on his parents for the care he needs 24 hours a day.
Panorama reveals that his father, Kennedy, says even though he loves his son, if they had another baby born as early as Bright, he would say "turn off the machine, there is no need to continue".
Panorama: Miracle Baby Grows Up will be broadcast on Wednesday, 22 September 2004 at 21:00 BST