Sharp drop in mortality after 41 weeks of pregnancy

(Press-News.org) The proportion of babies dying before and during labor after 41 weeks of gestation has fallen by 47% in Sweden in a relatively short time. This is the result of a major national study. The reduction has occurred since the procedures around induction have changed.

A pregnancy normally lasts around 40 weeks. However, a fairly high proportion of women, 22%, pass their due date and are pregnant for 41 weeks or longer. Although Sweden generally has a very low risk of stillbirth and death within the first month of life, the risk increases the longer the pregnancy continues past 41 weeks of gestation. The question that then arises is whether the woman should be induced.

The current study, published in the journal PLOS Medicine, is based on registry data on more than 150,000 births in Sweden where the women were one week or more after the expected date of delivery.

The aim was to investigate how infant mortality and morbidity in late-term births have changed since 2020, when most maternity hospitals in the country changed their practices for induction.

The new procedures were a response to research findings from 2019 that showed that fewer infants died if women were induced as early as after 41 gestational weeks, compared to 42, which was the standard practice at the time. The shift in 2020 meant a more active management where women began to be offered induction at 41 weeks or individual assessment of whether induction was needed.

Risk almost halved

When the researchers now compare the periods 2017-2019 and 2020-2023 (until September 2023 (incl.)), the results show a 47% decrease in the proportion of stillbirths or infants dying within four weeks. In the first period, 124 infants (1.7 per 1 000) and in the second period 74 infants (0.9 per 1 000) died during labor after 41 gestational weeks or more. The periods covered approximately the same number of these births.

The study also shows that a composite measure of mortality and severe morbidity in the neonatal period was lower in the latter group, after 2020. At the same time, there was a slight increase in the rate of emergency caesarean sections, but the rate of caesarean sections increased even more in gestational week 39-40.

Researchers are unable to determine exactly which interventions led to the improved survival of the children. It is therefore unclear whether this is mainly due to routine induction after 41 gestational weeks or whether intensive monitoring is sufficient to select women who should be recommended for induction.

One of the driving forces behind the study is Karin Källén, Statistician and Professor of Clinical Epidemiology in Obstetrics and Gynecology at Lund University:

“The results show a clear decrease in both neonatal death and severe morbidity and an increase in the number of inductions and emergency cesarean sections. With around 22 000 women annually in Sweden still pregnant at 41 weeks, 18 infant deaths have been prevented annually, says Karin Källén.

Good scientific basis

Ulla-Britt Wennerholm is Adjunct Professor of Obstetrics and Gynecology at Sahlgrenska Academy, University of Gothenburg. She also had a major research role in SWEPIS (Swedish Postterm Induction Study), published in 2019, which led to the change in care routines.

“The present study gives support for a more active management with induction or individual assessment at 41 weeks. The difference between the pre- and post-2020 periods was large, but at the same time it is important to emphasize that the absolute risk to an individual woman and her baby is very small, regardless of whether the delivery takes place after 41 or 42 weeks,” she says.

The study in PLOS Medicine is based on data from the National Pregnancy Registry, the Swedish Neonatal Quality Registry and Statistics Sweden. The women included were at least one week overdue and had low-risk pregnancies in the sense that they were healthy, were expecting a baby in an occipito-anterior (head first) position and had not previously had a caesarean section.

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