Half of premature babies of 27 and 28 weeks gestation are now born in a specialist unit due to improvements in management of care, research suggests.
Transferring women at high risk of premature labour to a specialist centre for delivery has boosted the number of babies who benefit from the most intensive care.
However, researchers said there has also been an increase over the last decade in the proportion of babies needing transfer to another hospital in the first 24 hours or month after delivery.
A third of babies who are part of twins or triplets are also treated in separate units, highlighting problems with the number of cots available, they added.
The research, published online in the British Medical Journal (BMJ), looked at maternity units in England, Wales and Northern Ireland between 1998 and 2000 and units in England between 2009 and 2010.
It assessed the impact of a reorganisation of neonatal services in England after 2003 into managed clinical networks.
Overall, the number of babies delivered in specialist units rose from 18% to 49% in England between the two periods.
Survival was significantly higher in the latter period in England, rising from 88% to 94%.
The authors, from Imperial College London, said: “As the prognosis for very preterm babies is improved when they are born and have their initial care in highly specialist centres, the change in place of delivery we document represents an important improvement.”