The row over the 24-week abortion limit has intensified after it emerged survival rates for very premature babies have more than doubled at a top hospital.
A study from University College London Hospitals NHS Foundation Trust (UCLH) found survival rates for babies born alive between 22 and 25 weeks of gestation rose from 32% in 1981 to 71% in 2000.
The professor behind the research said it showed what could be achieved if staffing levels were kept consistent and adequate resources were pumped into units.
But many experts back the findings of the EPICure study of all UK units, which has indicated little improvement between 1995 and 2006 in the rates of survival to discharge home for babies born below 24 weeks gestation.
UCLH neonatal consultant, Professor John Wyatt, led the new study and gave evidence to last year's Commons science and technology committee, which found no scientific justification for lowering the 24-week limit.
He said the EPICure study gave much lower survival rates than he had found "and it has been argued that there has been no improvement in survival across the country as a whole since EPICure was undertaken in 1995.
"However, studies which average the results from a large number of maternity units obscure the effects of very marked variations in resources, staffing and experience in the care of extremely premature infants.
"It is also plausible that ethical and clinical policies vary between different units and there is published evidence to show that this will have an effect on survival rates."
Prof Wyatt said he fully acknowledged that his study had limitations because it only looked at a small number of babies.
But he said such studies were "hugely important because they provide information on the survival rates that can be achieved with consistent levels of staffing and resources, and with consistent policies."
