Most spontaneous births take place between 1:00 and 6.59am with a peak around 4am and a trough in the afternoon, according to UK researchers.
Their study has found that the time and day that women give birth can vary significantly depending on how labour starts and the mode of giving birth.
“Pronounced differences were seen depending on how labour started and the mode of giving birth”
The findings also have implications for managing maternity staffing levels, said the researchers.
In order to conduct the first national analysis to look at all aspects of time of birth in England, they analysed over five million births over a 10-year period.
They found 28.5% of births occurred between 9am and 4.59pm on weekdays. The remaining 71.5% occurred outside these hours at weekends and on public holidays, or between 5pm and 8:59am on non-holiday weekdays.
Just over half were spontaneous births following labours that also started spontanously. These were most likely to occur between 1am and 6.59am, with a peak around 4am, and a trough in the afternoon. They were slightly more likely to happen on weekdays than on other days.
Elective or pre-planned caesarean births accounted for 9.2% of births and were seen to occur mostly on weekdays between 9am and 11.59am, with a pronounced peak between 9am and 10:59am.
“This is useful research that will support maternity services to more effectively organise their staff”
Very few occurred between 5pm and 6.59am on weekday evenings and nights, and even fewer at any time at weekends and on holidays, noted the researchers.
Differences between days were most pronounced among pre-planned caesarean births, which rarely occur at weekends or on public holidays.
The highest numbers were recorded on Mondays and on weekdays after a holiday period, followed by Thursdays and weekdays before a holiday, reflecting staff working patterns.
Lastly, births after induced labours, which made up over a fifth of births, were more likely to occur at hours around midnight on Tuesdays to Saturdays and on days before a public holiday period. They were less likely to occur on Sundays, Mondays and during or just after a public holiday.
The study authors highlighted tat induced labours may lead to spontaneous births, operative births using forceps or ventouse or emergency caesareans. These three groups of induced births share a weekly cycle that has its highest peak on Friday night and its trough on Monday morning.
As in earlier analyses by day of birth, they noted that numbers reached their minimum level on Christmas Day and Boxing Day.
“A night-time labour and birth probably afforded the mother and newborn baby some protection”
The study, published in the journal PLOS ONE, was carried out by researchers from City, University of London in collaboration with University College London and the parent charity NCT.
Patterns of spontaneous birth have remained unchanged since the 1950s, but the researchers found overall birth patterns have changed since then, following the rise in rates of obstetric intervention.
It was also seen that the rising rates of elective or pre-planned caesarean section have concentrated increasing numbers of births onto weekday mornings.
In contrast, the data from the study shows that numbers of induced births peak at night, irrespective of the mode of giving birth.
As the timing of birth varies by how labour starts and the mode of giving birth, these patterns also have implications for midwifery and medical staffing, noted the researchers. They stated that appropriate levels of staffing were needed at all times in the evenings and at night.
Senior study author Professor Alison Macfarlane said: “Pronounced differences were seen depending on how labour started and the mode of giving birth, with 71.5% of births overall occurring outside the hours of 9am to 4.59pm.”
“It’s worrying that induction appears to be timed so that the babies are most frequently born around midnight”
Professor Macfarlane, an expert in perinatal health from City, highlighted that current trends in obstetric intervention at birth may work in “opposite directions”.
“Rates of induction are now rising, and induced births are more likely to occur at night, while rates of pre-planned caesareans are also rising and these are likely to be scheduled for morning hours,” she said.
“The research should be of interest to policymakers, as policies to increase community births may lower rates of obstetric intervention and affect these trends and impact on the overall timing of birth,” she added.
Lead author Dr Peter Martin suggested that “our evolutionary heritage” may help explain why births without intervention are most likely to occur at night or in the early hours of the morning.
“Our ancestors lived in groups that were active and dispersed during the day and came together to rest at night,” he said. “So a night-time labour and birth probably afforded the mother and newborn baby some protection.”
Senior NCT policy adviser Elizabeth Duff said: “It’s worrying that induction appears to be timed so that the babies are most frequently born around midnight, when senior staff are less widely available to assist if complications arise.
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“These findings should be acted upon by NHS managers to ensure their services provide women and babies with the best care at the right time,” she said.
Sean O’Sullivan, head of health and social policy at the Royal College of Midwives, said: “This is useful research that will support maternity services to more effectively organise their staff and rotas.
“Birth is however very unpredictable and maternity services must be staffed to ensure that unexpected surges in demand can be managed to continue delivering safe and high quality care,” he said.
He added: “It is also worth noting that this study focuses on birth and the work of midwives and maternity support workers of course encompasses much more than just birth.”
For example, he cited antennal and postnatal care and specialist work such as maternal mental health, bereavement care, infant feeding support and “much, much more besides”.