Specialist NHS baby care units are near breaking point because staffing levels have not kept pace with medical advances, a campaign group will claim today.

In a survey of neonatal care across the UK, Bliss, a premature babies charity, found that an extra 2600 nurses would be needed to meet guidelines on the treatment of sick and premature babies.

The shortfalls meant that in 2006 only 12 units had complied with the minimum staffing levels laid out by the British Association of Perinatal Medicine (BAPM) in 2001, down from 15 the year before.

The charity warned that this was placing babies' lives in danger, as there is a proven link between infant mortality and staffing levels.

Among intensive care units, where critically ill babies needing constant supervision are treated, just under one-half were operating at or below half the recommended staffing levels.

Soaring occupancy levels also led hospitals to refuse admissions, the report found.

On average, hospitals turned patients away for two weeks every six months, with the worst problems being experienced in intensive care units.

Most units were operating above the 70% average occupancy level recommended by BAPM and one in eight of the most specialist units operated at an average occupancy of 100% or more for a whole year.

Overall, the number of neonatal nurses had risen in the NHS, the report found. But this had not kept pace with rising levels of demand, as advances in treatment have led to premature infants surviving from an earlier age and requiring more treatment.

Moreover, there was evidence that 45 hospitals had cut the number of neonatal nurses and that ratios of nurses to babies were worsening.

The survey, Too Little Too Late - are we ensuring the best start for babies born too soon?, was based on questions put to 195 neonatal units across the UK using freedom of information legislation. In Scotland, 14 out of the country's 15 neonatal units responded.

Andy Cole, chief executive of Bliss, said: "Bliss is concerned that the government still gives less priority to intensive care for babies than for adults and children, even though all the evidence points to a neonatal service that is on the brink of collapse.

"The Department of Health's recent commitment to provide extra midwives is a step in the right direction for maternity services.

"We now need to see the same commitment to ensuring there are adequate numbers of trained neonatal nurses for those babies born sick or premature."

The Bliss survey also flagged up problems in neonatal transport but found that Scotland had a good record on this front, in contrast to south of the border.

BAPM recommendations state there should be one nurse to each baby in intensive care units.

In high-dependency care, there should be at least one nurse to every two babies and, in special care, there should be at least one nurse to every four babies.

A recent study of babies born under 3lb 5oz or less than 31 weeks' gestation showed that when staff numbers were improved to the guideline levels, infant mortality rates dropped by 48%.

A spokeswoman for the Scottish Government said it was aware of issues in neonatal service, which would be looked at by the neonatal subgroup of the Maternity Services Action Group.

"It has been charged with carrying out a comprehensive review of the service, including cot complement, cot placement, staffing ratios and skill mix," she said.

"We will give full consideration to the findings and recommendations of the neonatal sub-group when the report becomes available in the autumn."