Risks of night births studied

“Pregnant women have been warned their delivery is nearly 50% more likely to go wrong if they give birth at night rather than during the day due to poor staff cover”, reports the Daily Mail.

The news story is based on a seven-year study of hospital births in the Netherlands. It found an increased risk of adverse outcomes in newborn infants with evening and night births in hospitals, and with night births in specialist centres. These adverse outcomes were uncommon: in 655,961 hospital deliveries, 1.7% had an adverse outcome and in 0.19% of the births, the newborn died.

The study’s strengths are its large size and the completeness of the data that was collected. However, several factors may have contributed to this association, and it is not possible to say conclusively that poor staff cover during the evening and night shifts were responsible, though it may have contributed.

Furthermore, as this study was in the Netherlands, it is not known if these results apply to the UK or other countries, which may have very different obstetric care protocols and organisation of staff and medical training posts.

Where did the story come from?

The study was carried out by researchers from the University Medical Centre Rotterdam and the University of Amsterdam. The research received no funding. The study was published in the peer-reviewed British Journal of Obstetrics and Gynaecology.

The news reports have generally reflected the main findings of this research, but have not been able to analyse these results in their full context or recognise some of the difficulties in interpretation. It is not correct to conclude from this study that the increased risk of adverse outcomes with night-time deliveries is due to poor staffing.

What kind of research was this?

This aim of this Dutch cohort study in hospitals in the Netherlands was to investigate whether time of birth, and certain features of the maternity unit affected the risk of newborn deaths or other adverse outcomes. The researchers used national registry data to examine births in all 98 hospitals across the Netherlands between 2000 and 2006.

What did the research involve?

The researchers used the Netherlands Perinatal Registry to identify all pregnancies continuing beyond 20 weeks between 2000 and 2006. The Registry contains data on maternal characteristics, pregnancy and labour, and outcomes in the newborn.

After excluding multiple births, home births and deliveries at hospitals that had not participated in the registry for two years, they were left with 792,954 births in 98 hospitals. Further refinement of the hospital birth dataset excluded foetal deaths during pregnancy, very premature babies and babies born with congenital malformations, as all of these would normally be cared for in specialist centres.

Births in specialist perinatal centres (109,858 births) were analysed separately from those in hospitals. From this data, foetal deaths during pregnancy and births prior to 22 weeks of pregnancy were excluded.

These further exclusions resulted in a final data set of 655,961 births in hospitals and 108,445 births in specialist perinatal centres.

Evening deliveries were defined as happening between 6pm and 11.59pm, and night deliveries between 12am and 7.59am. Survey data was collected on the staffing and organisation within the hospitals (such as whether it was a teaching hospital, and the numbers of obstetricians, midwives and doctors in training posts).

The main outcomes considered were perinatal mortality (death during delivery or within the first seven days following birth), and adverse outcomes in the newborn (including perinatal mortality,
poor score on a standard measure of neonatal health immediately after birth [5-minute Apgar score below 7] or transfer of the newborn to a neonatal intensive care unit).

Statistical analyses were conducted to examine the relationship between organisational factors and pregnancy and delivery characteristics with adverse outcomes in the newborn. The analyses took into account factors that can affect the risk of adverse outcomes, including the mother’s age, number of previous children, type of delivery, pregnancy length, ethnicity and calendar year of the birth.

What were the basic results?

Of the 655,961 hospital deliveries, 1.7% (11,118) were associated with an adverse outcome and 0.19% (1,206) with death in the newborn. Of the 108,445 births in specialist perinatal centres, 11.7% (12,705) were associated with an adverse outcome and 1.8% (1,915) with death in the newborn. Of the births analysed, 53% were to first-time mums and 20% of mums were over 35 years old. Approximately half of the births occurred during the evening and night-time hours.

In hospitals, evening births had a 32% increased risk of death in the newborn compared to daytime births (odds ratio [OR] 1.32, 95% confidence interval [CI] 1.15 to 1.52). Night births had a 47% increased odds of newborn death compared to day births (OR 1.47, 95% CI 1.28 to 1.69). In specialist centres, only night-time births had an increased risk(20%) of newborn death (OR 1.20, 95% CI 1.06 to 1.37). Compared to day births, evening births had a higher risk for an adverse outcome (OR 1.30 for hospitals and 1.21 for specialist centres) as did night-time births (OR 1.28 for hospitals and 1.25 for specialist centres).

Further analysis found links with various other factors. There was a clear increased risk of adverse outcomes for premature births (prior to 37 weeks) compared to term births (at 40 weeks), both in hospitals and specialist centres. Emergency caesarean sections were also associated with an increased risk of adverse outcomes in hospitals and specialist centres compared with spontaneous delivery, but with a decreased risk of death in the newborn in specialist centres. There was no clear relationship between the annual number of deliveries and the risk of adverse outcomes. More senior staff were associated with a significantly reduced risk of adverse outcomes, but did not affect risk of perinatal mortality in hospital deliveries.

How did the researchers interpret the results?

The researchers conclude that hospital deliveries at night are associated with increased perinatal mortality and adverse perinatal outcomes. They say that the time of delivery and other organisational features such as staff experience may explain the variation between hospitals.

Conclusion

This is a good quality study, but the data needs to be interpreted in the correct context. These adverse outcomes were uncommon, and of the 655,961 hospital deliveries analysed, 1.7% had an adverse outcome and 0.19% were associated with the newborn’s death. The rates in specialist centres were higher, but this is likely to be because these centres deal with more complicated pregnancies and births.

It is difficult to identify specific reasons why evening and night-time births in hospital were associated with an increased risk of adverse outcomes. It cannot be assumed that it is due to reduced staffing levels or facilities at night, although these and other factors may contribute. As the researchers say, they had limited information on actual staffing levels just before and during each individual delivery, and therefore they could not look at the effects of these factors. The relationship may even be due to an unknown biological factor.

In examining the links between adverse outcomes and the numerous possible contributing variables, it is difficult to unpick the exact cause and see how the variables interact with each other. There is also the increased risk of chance findings when examining associations with many variables.

The study was in births in hospitals in the Netherlands and therefore the results may not apply to the UK. The UK may have very different obstetric care protocols, including staff numbers and facilities during the evening and night.