About 100 babies in Britain are dying each year because they are born outside normal working hours and do not get the best possible care, researchers said Friday.

A study of more than 500 infant deaths in Scotland found that babies born at weekends or outside the hours of 9am to 5pm, Monday to Friday, were significantly more likely to die — mainly from a lack of oxygen — than those born at other times.

One possible explanation for the trend could be a lack of immediate access to senior doctors at weekends and during the evenings, the researchers said.

The increased risk in the first four weeks of life was equivalent to an extra one or two deaths for every 10,000 live births, which doctors said raised concerns about out-of-hours maternity services.

Gordon Smith, Professor of Obstetrics and Gynaecology at the University of Cambridge, who led the study, said that there was no reason why the findings from Scotland were not being replicated across Britain. This would amount to the deaths of about 100 babies each year.

“These babies are all essentially normal and have grown normally,” he said. “We would have anticipated that they would have a normal life expectancy. But something has happened around the time of birth that has asphyxiated them.”

The study comes after research published last month found that patients were more likely to die if they were admitted to hospital at weekends.

Complications during a normal birth can include the umbilical cord becoming wrapped around a baby’s neck, or other factors that could be detected and dealt with by experienced hospital consultants. However, much obstetric care at night and on weekends is covered by junior doctors and, in most maternity units, consultants are on call and not present.

For the latest study, published in the British Medical Journal Friday, Professor Smith and his colleagues analyzed 539 neonatal deaths among more than a million births in Scotland between 1985 and 2004. The deaths occurred at birth or in the first four weeks of life and were not related to congenital abnormalities or prematurity. About half were caused by lack of oxygen. The experts said that the higher fatality rate out of hours was due to “a significant excess risk” — 70 percent higher — of oxygen starvation.

The Royal College of Obstetricians and Gynaecologists (RCOG) said previous data from the National Patient Safety Agency showed that the most severe incidents relating to babies occur between