Inducing labor at 41 weeks safer than 'wait and see' approach

For late-term pregnancies, inducing labor at 41 weeks may be safer than waiting until week 42, a large Swedish study suggests.

The randomized trial across 14 hospitals was halted early because stillbirths and newborn death were markedly higher with “expectant management” until the 42nd week of pregnancy compared to inducing labor at 41 weeks, the researchers report in The BMJ.

There were no other differences between the two groups in adverse outcomes for infants or mothers, so induction at 41 weeks should certainly be offered to mothers, the study team concludes.

“Neonatal mortality and morbidity, as well as maternal morbidity, increase when the pregnancy lasts more than 40 weeks, and the risks increase further as the pregnancy advances,” said Ulla-Britt Wennerholm of Sahlgrenska University Hospital in Gothenburg, Sweden, who led the study.

“There is still uncertainty about obstetric management of late-term pregnancies and the optimal time to induce labour,” she told Reuters Health by email.

About 14% of stillbirths are associated with prolonged pregnancy worldwide, the study authors note in their report. The World Health Organization recommends induction at 41 weeks, but countries often vary in their practices.

Wennerholm and colleagues compared the induction of labor at 41 weeks with a “wait and see” approach and induction at 42 weeks if labor had still not occurred. At 14 hospitals in Sweden, between 2016 and 2018, a total of 2,760 women with low-risk, uncomplicated pregnancies lasting more than 40 weeks were randomly assigned to one of the two groups.

The researchers looked at a composite of adverse outcomes for the baby, including stillbirth, neonatal death, brain hemorrhage, oxygen deprivation, troubled breathing, convulsions and required ventilation. They also looked at complications for mothers, such as cesarean delivery or vaginal birth with instruments, prolonged labor, use of epidural anesthesia and hemorrhage.

The research team had planned to recruit 10,000 women over time, but they cut the trial short when they saw a significantly higher rate of infant mortality in the expectant management group. There were five stillbirths and one neonatal death among the women who waited until week 42, compared with none in the group induced at 41 weeks.

Birth complications didn’t differ statistically between the two groups - with 33 in the induction group and 31 in the expectant management group. Rates of cesarean deliveries, vaginal births and other maternal consequences were the same.

“The routine at most Swedish clinics, and also in some other countries, is still to induce at 42 weeks, so it was unexpected that we had to stop the study early,” Wennerholm said. “The study was stopped for ethical reasons because of an unexpected higher rate of perinatal mortality.” Future studies will need to focus on this aspect of perinatal mortality to confirm the findings and understand the reasons, she said. The research team is now analyzing individual patient data from the trial to understand if certain groups of women face a higher risk. They’re also conducting a health technology and economy analysis to determine how to change national guidelines - and how that may affect expectant mothers and economic costs.

“Choice is important with maternity care, and clear information about available options should be accessible to all pregnant women, enabling them to make fully informed and timely decisions,” said Sara Kenyon of the University of Birmingham in the UK, a professor of evidence-based maternity care who coauthored a commentary accompanying the study.

Although the overall risk of an adverse outcome at 42 weeks is low for both the mother and baby, induction at 41 weeks may be safer, the commentary points out. Now hospitals and maternal clinics must find ways to consider and implement this advice.

“Pregnancies that continue past 41 weeks are usually safe and straightforward, but there is a small yet significant increase in stillbirth risk past this, so induction of labour at 41 weeks is a reasonable option for women,” Kenyon told Reuters Health by email. “We support the continual review of clinical guidelines as new evidence emerges to ensure best practice.”