The research looked at babies born before 26 weeks gestation
A major study has found no significant improvement in the survival rate for very premature babies over the last 10 years, the BBC has learned.
The research showed babies born above 24 and 25 weeks gestation were more likely to live than in the past.
But there was no significant improvement in survival of babies born before 24 weeks - the current time limit for abortion.
The data for England comes just weeks before MPs are due to debate the issue.
The study, known as Epicure 2, analysed all severely premature births in England in 2006 and compared their survival outcomes with those born in 1995.
Interview with Professor Kate Costeloe
In all there were around 1,300 live births before 26 weeks gestation, of whom 952 babies survived long enough to be admitted into neonatal intensive care.
Of this group 52% survived compared with 40% in 1995, with significant improvements above 24 weeks gestation.
Professor Kate Costeloe a neonatal paediatrician from Barts and the London NHS Trust collated the data and will present it to the Royal College of Paediatrics and Child Health's annual meeting next week.
She told the BBC: "There has been a statistically significant increase in survival at 24 and 25 weeks, but not at 23 weeks."
Forty per cent of babies born at 23 weeks die in the labour ward, the study found.
Severely premature babies who do survive very often have long term problems stemming from the lack of lung and brain development.
NEO-NATAL UNIT SURVIVAL
23 weeks - 26%
24 weeks - 47%
25 weeks - 67%
The research said there has been no reduction in the proportion of infants who have such problems over the last decade.
Professor Costeloe said it was particularly challenging to care for babies born before 24 weeks, primarily because their lungs and brains had not developed properly.
"It's going to be more difficult to achieve significant improvements for that population," she added.
In 1990 MPs reduced the abortion time limit from 28 to 24 weeks as a direct result of research which showed improvements in foetal viability.
Ann Furedi, of the pro-choice British Pregnancy Advisory Service said the law should remain as it is.
"When MPs look at the evidence, they will see there's no evidence to reduce the limit."
Liberal Democrat MP Evan Harris, who helped compile a Commons Science and Technology committee report on abortion law and medical development, said: "A change in the abortion time limit is not justified on the basis of medical evidence as this study shows."
But Josephine Quintavalle, of the pro-life group Comment on Reproductive Ethics, said that was not the case.
"Even if only one baby survives at 23 weeks, that's good enough evidence for me to say we should give the benefit of the doubt always to the child."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.