The present study, an individual participant data meta-analysis, is published in the journal PLOS Medicine. Most of the researchers are connected to the University of Gothenburg and the University of Amsterdam.

In Sweden and the Netherlands, the risk of a baby dying before, during or shortly after birth ("perinatal death") is generally very low. The same is true of the risk of harm or injury to the baby in conjunction with the birth. However, these risks -- of perinatal death and morbidity (ill-health, trauma or other injury) alike -- are known to rise somewhat, from a low level, the longer a pregnancy goes on after the 40th week.

The purpose of the meta-analysis was to compare outcomes from induction at 41 and expectant management and if not delivered induction at 42 weeks, by combining individual studies addressing the same question. To date, in some respects, it has been unclear what measures best protect the woman and child.

Three randomized studies of the same question have been published, all since the year 2000: SWEPIS (the SWEdish Post-term Induction Study), covering 2,760 women; a Dutch INDEX study (INDuction or Expectant management) of 1,801 women; and a Turkish study of 600 women.

The Swedish and Dutch studies were able to contribute findings at individual level, and the Turkish study was also included in the aggregate appraisal of perinatal death and the proportion of cesarean deliveries. All the women had reached 41 weeks, were healthy and expecting one baby when they participated in the respective studies.

Of the 4561 women included in the analysis of individual data, 2,281 were assigned for induction at 41 full week. In this group, 80 percent underwent induction. For the others, the delivery started spontaneously.

In the Expectant Management group of 2,280 women, spontaneous delivery start was awaited until 42 weeks when induction was otherwise planned. This has been the routine management practice at most birth centers in Sweden and the Netherlands in uncomplicated pregnancies. In the Expectant Management group, 30 percent of the women needed to be induced, while for the others labor began spontaneously.

In terms of the combination of perinatal death and severe morbidity, 10 (0.4%) were affected in the group induced at 41 weeks and 23 (1.0%) in the 42 week group. The difference between the groups is statistically significant. These results hold for women who deliver for the first time. For women who already gave birth once the number of perinatal deaths and morbidity was too low to demonstrate any effect.

There was no difference in the women's state of health after birth between the groups. The proportions of cesarean sections and of instrumental births, using a ventouse (suction cup) or forceps, were also comparable.

Mårten Alkmark, a doctoral student in obstetrics and gynecology at Sahlgrenska Academy, University of Gothenburg, and senior consultant physician at the University Hospital, is one of the two first authors of the study.

"Being able to combine studies at individual level is a good, robust way of investigating questions where what we're studying is very unusual. It means that we've increased the number of women taking part, thereby also boosting the reliability of the results," Alkmark says.

"Our study shows, in agreement with previous research, that the risks of morbidity and perinatal death are lower when induction is carried out at 41 weeks than when it's done at 42 weeks, while it doesn't increase the risks of impaired health in the mothers."

Esteriek de Miranda, assistant professor of Amsterdam UMC of the University of Amsterdam and one of both last authors: "This reduction in risk was only found for women having their first childbirth, not for women who had given birth already one or more times, earlier induction had no benefit for these women and their babies."

Henrik Hagberg, professor of obstetrics and gynecology at Sahlgrenska Academy at the University of Gothenburg and senior consultant physician at the Sahlgrenska University Hospital, is one of the co-authors.

"If these results are extrapolated to Swedish conditions, where roughly 20,000 women a year are still pregnant at 41 weeks, one might prevent at least 100 cases a year of severe illness or death in the babies when they're induced at 41 weeks' gestation. The other side of the coin is that a lot of inductions then have to be done. To save one child from severe illness or death, statistically, 175 women have to undergo induction at 41 weeks," Hagberg says.

Judit Keulen, doctoral student of Amsterdam UMC and University of Amsterdam and one of both first authors:"Choosing for expectant management means an overall 99% chance of a good perinatal outcome for all women, for multiparous women choosing expectant management, the chance of a good outcome is not different than after induction of labour."

Ulla-Britt Wennerholm, senior clinical physician and associate professor of obstetrics and gynecology at Sahlgrenska Academy at the University of Gothenburg, is one of the two senior authors.

"Pregnant women whose pregnancies last 41 weeks should be informed about the advantages and disadvantages of induction, and those who then want to be induced should be offered this option," Wennerholm says.

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Materials provided by University of Gothenburg. Note: Content may be edited for style and length.

Journal Reference:

1. Mårten Alkmark, Judit K. J. Keulen, Joep C. Kortekaas, Christina Bergh, Jeroen Van Dillen, Ruben G. Duijnhoven, Henrik Hagberg, Ben Willem Mol, Mattias Molin, Joris A. M. Van Der Post, Sissel Saltvedt, Anna-Karin Wikström, Ulla-Britt Wennerholm, Esteriek De Miranda. Induction of labour at 41 weeks or expectant management until 42 weeks: A systematic review and an individual participant data meta-analysis of randomized trials. PLOS Medicine, 2020 DOI: 10.1371/journal.pmed.1003436