The idea that babies born at the weekend are at increased risk because their delivery is handled by inexperienced or skeleton staff has been debunked by research.
More premature babies are born at weekends
Studies carried out in the 1970s and 1980s suggested that it was safer to give birth on a weekday.
However, a new analysis of 1.5 million births in California between 1995 and 1997 has found no evidence to back up this theory at all.
The researchers, from Stanford University, believe the previous research was flawed because it failed to take into consideration the fact that there are a greater proportion of emergency deliveries of premature babies at weekends.
Lead researcher Professor Jeffrey Gould said: "The fact that there is a proportionally higher percentage of very tiny babies - who are more likely to die - born on weekends than during the week inflates the observed mortality rate."
The analysis found the percentage of very low-birth weight babies - defined as weighing less than 53 ounces or 1,500 grams - rose from 0.95% of all weekday births to 1.11 percent of weekend births.
As a result, the death rate among newborns was higher at weekends - 3.12 per 1,000 at weekends compared to 2.80 per 1,000 births on weekdays.
But this discrepancy disappeared once low-weight premature babies were removed from the equation.
Professor Gould said: "The battle to prevent delivery of these sickest foetuses can as easily be lost on the weekend as during the week."
Overall, there was a 17.5% decrease in births at weekends.
Nine to five service
Belinda Phipps, chief executive of the UK National Childbirth Trust, told BBC News Online there was concern in the UK that the NHS was basically a "nine to five" service, and that it was more risky to give birth at weekends.
"However, there is evidence to show that the vast majority of medical interventions do not make things better, and some may make things worse," she said.
"So it could be argued that perhaps it is better to give birth at weekends."
Ms Phipps said a similar belief had grown up about the safety of home births.
Even though it had been disproved that home birth was any more risky, the general perception had put many women off the idea.
The research is published in the Journal of the American Medical Association.