Picking the time of day to give birth may not be a choice very many women can make, but it could influence her chances of a smooth delivery, new research shows.

In a study of more than 700,000 births at all Dutch hospitals between 2000 and 2006, researchers found that the risks of newborn death and admission to the neonatal intensive care unit were higher with nighttime than daytime deliveries.

The findings, say the researchers, are in line with trends in other studies not only in obstetrics, but in hospital intensive care units as well.

Overall, the new study found, infants at smaller community hospitals who were born in the evening (between 6 p.m. and midnight) or overnight into early morning (between midnight and 8 a.m.) were 32 percent to 47 percent more likely to die than those born during the day.

Larger medical centers that would see more high-risk pregnancies - so-called tertiary centers - did not have as much of a difference between night and day. At these hospitals, only overnight births - as opposed to evening births - were linked to an increased risk of newborn death.

The findings were similar when the researchers looked at the risk of all adverse birth outcomes together.

But they stress that, in developed countries, serious complications are rare no matter what time of day or night a woman delivers.

“It is very important indeed to realise that risks are generally low and that the level of care in these kinds of Western countries is high,” senior researcher Dr. Eric A.P. Steegers, of Erasmus University Medical Center in Rotterdam, told Reuters Health in an e-mail.

Of the nearly 656,000 singleton births at community hospitals, between 0.05 and 0.09 percent of infants died during or soon after birth. Rates were higher among infants born at tertiary hospitals, but were still less than 1 percent.

It’s possible, Steegers said, that the increased risks reflect the fact that fewer senior staff members - including obstetricians, neonatologists and anesthesiologists - are available during night shifts.

Supporting that idea, the researchers found fewer infant deaths and complications at community hospitals when senior staff were present. At night, when such staff are at home on call, less experienced doctors may be making the initial decisions on how to manage high-risk situations.

Steegers said that more research is needed, however, to understand the extent to which hospital organization plays into the higher risk of childbirth complications at night.

It’s also possible that staff fatigue is a factor, since night-shift work is at odds with the body’s natural rhythms. But unfortunately, naps don’t seem to do the trick: It may take up to half an hour for sleepy minds to get back up to speed after a slumber, the researchers note.

Even if organizational factors at hospitals do explain the higher nighttime risks, Steegers said, it is not clear whether revamping the system would eliminate those risks.

For example, he noted, it might be possible to have senior staff available 24 hours a day if there were fewer hospitals providing obstetrics care. But fewer centers could well mean that some women would be delayed in getting to the hospital, which could increase the odds of complications.

SOURCE:  BJOG, online May 25, 2010.