Premature babies are at a high risk of disability
There has been a dramatic rise in the number of babies being born prematurely in England, a charity has warned.
Tommy's baby's charity highlights NHS figures showing 8.6% of babies were born early in 2006/7, after remaining around 7% for the previous 15 years.
It said the increase equated to an extra 10,554 premature births. Babies born early are at increased risk of dying or developing serious problems.
Experts said the rise was partly due to more older - and younger - mothers.
But the NHS Information Centre, which published the latest statistics, said there had been changes to the way data had been collected which might have affected the rise.
Being born prematurely - before 37 weeks - is responsible for 75% of neonatal deaths in the first month of life, and the majority of intensive care admissions.
Babies are also at an increased risk of disability and illness extend throughout childhood and later life.
Tommy's says there are a number of risk factors which may lead to premature birth including maternal smoking, infections in the womb, twin or triplet pregnancies.
Being a teenage or older mother is also linked to increased risk, as is being underweight.
Babies can also be delivered prematurely if doctors decide the health of the mother or baby is at risk, perhaps because the mother has developed pre-eclampsia or if the baby is abnormally small.
Dr Rebecca Jones, from Tommy's Manchester Research Centre at St Mary's General Hospital, said: "It is hard to tell from the figures whether the increase is due to spontaneous births, when the woman goes into labour early, or whether it is due to medically-induced premature delivery.
"Potential reasons for the increase may be more mothers having babies at a young or late age, more multiple pregnancies because of IVF, changes in smoking rates, or changes in the general health of the population."
But she added: "This is a worrying increase and it highlights the need for more research in this area, to understand the reasons for premature birth and develop new treatments."
Ronald Lamont, a spokesman for the Royal College of Obstetricians and Gynaecologists, said there had been disparities in how different hospitals recorded premature births, and it was possible this had changed.
"If a baby is born at 36 weeks and six days, some will round that up to 37 weeks, when they should round it down to 36."
He added: "Another reason is that now neonatal doctors can keep more babies born very early alive, so obstetricians like me can deliver them.
"And if there is a problem with the pregnancy, doctors do have the option to deliver babies safely."