According to lore, you don't want the first car that rolls off the assembly line any Monday morning, after the autoworkers have been away for two days. And you don't want to be the first person to use the latest version of software pushed out after two consecutive all-nighters by a company's entire staff.

Now, thanks to a large new study by researchers at the Johns Hopkins University School of Medicine, we know that you also do not want your children to have urgent or emergency surgery during the weekend, even relatively uncomplicated procedures such as appendectomies, hernia repairs, or work on a nasty bone fracture.

According to the research, published in the Journal of Pediatric Surgery, the outcome of weekend surgeries for those and other conditions is more likely  to end in death or complications, and to require a blood transfusion.

"This is data confirming what we expected," said Seth Goldstein, a surgical resident who led the study. "Those of us who spend a lot of time in the operating room know that nights and weekends are a different beast."

When Goldstein and his colleagues compared more than 327,000 weekday pediatric surgeries with more than 112,000 performed on weekends over a 22 year period, they found that the latter were 40 percent more likely to result in complications such as accidental lacerations or punctures, infections, hemorrhages or wounds that reopen or don't heal in the first place. Although the difference in the number of deaths was statistically significant, the number of mortalities was tiny in comparison with the number of surgeries, a positive finding of the study.

Weekend surgeries also resulted in 14 percent more blood transfusions.

The study did not investigate why these results occurred, but Goldstein said in an interview that it is almost certainly a "systems issue." On weekends, hospitals have fewer staffers, teams are often comprised of people who are not familiar with each other, and ancillary services are not as readily available. Surgeons working on weekends may not specialize in pediatric surgery, he said, which may account for the higher rate of blood transfusions -- a more conservative strategy during surgery but one that carries more risks of side-effects.

"We know it's not because patients are bleeding more," Goldstein said. "The surgeons or the anesthesiologists may be being more risk averse because they don't take care of children all the time, or don't do the procedure all the time."

The study noted that other researchers have found the same weekend-weekday outcome discrepancy among people treated for diverticulitis, strokes, pneumonia, traumatic brain injuries and other conditions that put them in intensive care.

The current study controlled for the types of problems presented during the week and on weekends, whether the patient was insured, race and gender, among other factors, and found that they did not affect the results. They did find that children admitted during the weekend were more likely to be classified as emergencies and "slightly" less likely to be seen at teaching hospitals or facilities located in the West.