Babies born on a weekend face a greater risk of developing complications or being stillborn, according to researchers from Imperial College London.

The researchers investigated data from 1.3 million births in England that took place from April 2010 to March 2012 and found an association between the day a baby is born and the likelihood of developing emergency health problems within the first three days of birth, being stillborn (perinatal death) or having injuries.

The researchers reported that most births took place on a Thursday, while the fewest births happened on a Sunday. They also found that babies are more likely to be stillborn on Thursdays, Saturdays and Sundays. On the other hand, babies are less likely to be stillborn on Tuesdays.

For every 1,000 babies born, there were 6.5 perinatal deaths. This rate increased to 7.1 on Saturdays and Sundays.

"In our paper we tried to account for the fact that differences in rates of complications on different days may be due to chance, or that births on certain days are more complicated in some way," study author Paul Aylin said in a news release. "However, even after making these adjustments, we found the rates of complications vary on different days. We don't know what causes this difference."

The researchers noted that mothers faced a greater risk of developing infections when they were admitted on weekends. The infection rate of mothers was only 8.2 on weekdays, but this rose to 8.7 on weekends.

"We have been able to present a detailed and comprehensive assessment of the 'weekend effect' in this important area of healthcare. However, this is a study based on administrative data and so we did not observe the quality of care directly," lead researcher William Palmer said in the news release. "The public should reasonably expect high quality care at all times, and this paper suggests that managers and clinicians in maternity care need to seek further assurance that their services are providing consistently good care throughout the week."

The study was published Nov. 24 in the journal BMJ.