A new study has cast doubt on the widely-held assumption that there is a higher risk of neonatal death for births outside working hours and at weekends.
Despite previously reported research suggesting a significantly higher risk of death, a new analysis of neonatal mortality among over six million births in NHS maternity units over 10 years suggested that for almost all births, being born 'out of hours' is as safe as being born during the standard working day.
Researchers from City University London performed a retrospective cohort study linking birth registration, birth notification, and hospital episode data to assess mortality risk by timing and mode of birth among 6,054,536 liveborn singleton births in NHS hospitals in England from 2005 to 2014. This enabled them to analyse births in great detail, including stratifying them by how labour started (spontaneous, induced, or no labour), by the type of birth (spontaneous, assisted with forceps or ventouse, or Caesarean), and by both time of day and day of birth, as well as taking account of obstetric risk.
No Overall Higher Risk for Out-of-Hours Births
Their study, published in BMJ Open, found that contrary to the previously assumed 'weekend effect', being born outside working hours (which they categorised as 7am to 7pm in the NHS) did not carry a significantly higher risk of death to the baby from anoxia or trauma, when compared with births during working hours.
A previously published study of 1.3 million births in England that looked at the day of the week of the birth, but not the time of day, had concluded that the rate of stillbirth, death during pregnancy, or death in the first week after live birth was higher at the weekends than during the week.
Another study of over a million births in Scotland that excluded stillbirths but included the time of day in its analysis found that neonatal deaths in the first month after live birth were higher outside working hours during the week.
The new study excluded stillbirths, reasoning that over 90% of stillbirths are known to occur prior to the onset of labour, and were therefore unlikely to be affected by care at birth. In the majority of the remaining 10% of cases, it is unknown whether the stillbirth occurred before or during birth.
After adjustment for confounders, the researchers found no significant difference in the odds of neonatal mortality attributed to asphyxia, anoxia or trauma for births outside normal working hours compared with those within working hours, for either spontaneous or instrumental births.
In addition, stratification of emergency Caesareans by onset of labour showed no difference in mortality by birth timing for emergency Caesareans after spontaneous or induced onset of labour.
Higher Risk for Out-of-Hours Emergency Caesareans Without Labour
However, the team did find higher odds of neonatal mortality, both overall as well as mortality attributed to asphyxia, anoxia or trauma, for births involving out-of-hours emergency Caesareans without labour – which account for around 2% of births in England. These births carried 1.56-fold (95% CI 1.15 to 2.11) higher risk of neonatal death when they occurred at night on weekdays, and had an odds ratio of 1.75 (95% CI 1.24 to 2.47) at night-time on weekends and holidays, compared with births during working hours.
Even so, the researchers noted, as neonatal death is a rare event, this higher relative risk translates to a small absolute difference in mortality risk, accounting for an estimated 46 neonatal deaths in total – 0.4% of all neonatal deaths – over the 10-year study. Neither of the previous studies were large enough to identify this small subgroup of births with a higher risk, they said.
Emergency Caesareans without labour have "by far the highest crude rates of neonatal mortality", the researchers noted. "As such, these births represent a cohort of mothers and babies with high risk, emergent conditions that are, by nature, likely to be unpredictable."
The authors concluded: "The apparent 'weekend effect' may result from deaths among the relatively small numbers of babies who were coded as born by emergency Caesarean section without labour outside normal working hours."
Risk Reduction Should Focus on Small Subset of Emergency Births
They recommended that based on this evidence, "attempts to reduce risk should focus on this smaller subset of emergency births, rather than regarding all births out of hours as dangerous".
They added that: "Further research should focus on understanding who goes on to have an emergency Caesarean birth without labour, and what aspects of care in the community or in hospital can help prevent critical incidents arising. Such aspects of care could include monitoring before birth or advice on healthcare-seeking behaviour for particularly vulnerable mothers or babies."
Asked to comment on the findings by Medscape News UK, Elizabeth Duff, senior policy adviser to the National Childbirth Trust, said: "It's impressive to see that this new research study, which analysed data from six million births over a 10-year period, has been able to explore in significant detail which babies were at greatest risk, and which were not.
"These results should help to reassure parents, although it should be noted that the study didn't include women who gave birth from 2015 onwards."
Principal investigator for the study, Alison Macfarlane, professor of perinatal health in the Department of Midwifery and Radiography at City University, said: "These findings are very reassuring and demonstrate the benefits of using a very large, linked dataset. They show that attention should shift from the timing of birth to identifying this very small subgroup of highly vulnerable women and the measures required to meet their needs."
The study was funded by the Economic and Social Research Council under its Secondary Data Analysis Initiative. The authors declared no competing interests.