The growing number of babies born prematurely, often to older and more overweight mothers, is costing the NHS almost £1billion a year more than if they were born full-term, research shows.

The first study to assess the financial burden of premature birth in England and Wales concludes that there are nearly £20,000 of additional care costs associated with the average premature baby. The research, published today in the American journal Pediatrics, indicates that most of the £939 million in extra costs are linked to neo-natal care such as incubation, and hospital readmissions.

The rate of premature births has increased sharply in recent years. In 2006, 7 per cent of all births were preterm — a total of almost 48,000 babies — rising to 8.6 per cent in 2007.

Factors linked to the increase include the age and weight of mothers, and the greater use of fertility treatments that raise the chances of a premature birth. About half of all mothers aged between 25 and 44 are now overweight or obese, according to latest statistics. Being a teenage mother or underweight also carries risks.

Babies born early — before 37 weeks — are more susceptible to serious problems including lung disease, eye and digestive tract conditions and increased risk of infection. They also account for the majority of intensive care admissions.

Tommy’s, the baby charity that funded the study, said that it showed the need for greater research into premature birth and methods for delaying or preventing it, such as delaying a woman’s contractions.

The study, conducted by Lindsay Mangham and Stavros Petrou of Oxford University’s Health Economics Research Centre,concluded that delaying premature births by a single week could save £260m a year, potentially.

Jane Brewin, chief executive of Tommy’s, said that the charity was working with the Department of Health and other stakeholders to draw up a strategy to address the problem.

“Given that the UK rate of premature birth is rising, the mammoth cost [of preterm births] is set to grow even larger. A plan must be developed which will target medical research resources to reduce premature birth.”

Andrew Shennan, Professor of Obstetrics at King’s College London, said that the delivery of a baby would never be affected by cost considerations. But it underlined the need for a greater attention in primary care to encouraging women wanting to become mothers, particularly those who had gained weight during a previous pregnancy, to lose weight, he said.

The study was based on a literature review, extensive research of current clinical practice and unit costs and consultations with leading clinicians. The information was used to produce a model that assigned a probability and a cost to possible outcomes associated with premature birth, including the need for neonatal care, mild disability, moderate disability, severe disability and death.

The study authors were then able to devise an average patient and associated cost for each week of prematurity, going back to gestation at 23 weeks. As well as neonatal healthcare, which made up most of the expense, other costs such as hospital readmissions, outpatient visits, special education needs and social services costs were also considered.

The model estimated total cost of all preterm babies born in 2006 over the first 18 years of their lives, in 2006 prices and with a slight discount. While the average cost of a child born full-term was estimated at £41,907, the extra cost for the average premature baby surviving to age 18 was £22,764. For babies born under 33 weeks and 28 weeks, the additional costs were £61,509 and £94,190 respectively.

Professor Peter Brocklehurst, director of the National Perinatal Epidemiology Unit (NPEU), University of Oxford, said: “The extent to which the costs associated with preterm birth are an economic burden has previously received little attention.

“These results emphasise the importance of preventing preterm birth. We propose that more effort is focused on preventing preterm birth in the UK and that research to prevent premature birth continues to be a strategic priority.”

The Royal College of Obstetricians and Gynaecologists said: “Lifestyle factors such as maternal obesity and binge drinking contribute to an increased risk of prematurity. It is important therefore to develop public health programmes aimed at preventing preterm birth.”

Andy Cole, chief executive of Bliss, the baby care charity, welcomed the research, but said that a baby was born needing specialist hospital care in the UK every six minutes, and these births were often a consequence of various unavoidable conditions.

“Our children deserve the optimum level of care and support that we can possibly provide . . . We cannot and should not judge a life by an economic metric.”

Tommy’s said that as well as the financial cost, the increase in babies born too early put added emotional strain on families who must deal with the lifelong consequences of a baby born too soon. While health and social care unit costs are well documented, costs in other areas such as special needs education, and costs incurred by families in caring for preterm children, are less well reported.