Inducing labor at 39 weeks is safe and linked to lower risk of C-section, study finds

A large new study adds to the evidence that inducing labor at 39 weeks is as safe as waiting for labor to occur naturally, a finding that experts say could change the way some women in the U.S. choose to give birth.

In a paper published Wednesday, researchers found that inducing labor at 39 weeks — when a pregnancy has reached full-term — didn’t result in any higher risk of perinatal death or severe health problems in infants. Even more striking: Women who had labor induced were less likely to have a C-section or experience problems with blood pressure than women who didn’t.

This finding overturns a long-held assumption that inducing labor at 39 weeks would raise a woman’s risk of C-section, experts said.

“I think it’s going to have a very big impact on obstetric practice not just in the U.S., but around the world,” said Dr. Kate Walker, an obstetrician and University of Nottingham researcher who has studied the health impact of induction but was not involved in the new paper.

Two of the nation’s leading obstetrics groups — the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine — said the findings show it’s a reasonable option for certain healthy women.

“ACOG and SMFM have reviewed the published results [and] determined that it is reasonable for obstetric care providers to offer an induction of labor to low-risk women after discussing the options thoroughly, as shared decision making is a critical element,“ the groups said in a joint statement.

ACOG recommends that elective induction should not be attempted before 39 weeks and induction is recommended after 41 weeks. Given the new findings, in the New England Journal of Medicine, the groups say induction at 39 weeks should be offered only to women who are healthy, planning their first delivery, and have had an ultrasound early in the pregnancy to confirm their due date.

The study follows a series of papers in recent years that challenged the long-held idea that induced labor increases the risk of C-section. A 2016 study, also published in the New England Journal of Medicine, found that inducing labor in women over age 35 — who are are more likely to end up delivering by C-section — didn’t increase their chances of needing the surgery. The new study is the largest randomized trial to look at induced labor at 39 weeks in healthy women.

“There is no hard data that’s holding this idea back at this point. It’s not just one study anymore,” said Dr. Michael Greene, chief of obstetrics at Massachusetts General Hospital. Greene, who wasn’t involved in the research, penned a related editorial that concludes the study should “reassure women that elective induction of labor at 39 weeks is a reasonable choice that is very unlikely to result in poorer obstetrical outcomes.”

The trial took place at 41 obstetrical centers across the U.S. that are part of the National Institute of Child Health and Human Development’s maternal-fetal medicine network. Researchers enrolled more than 6,000 women in the study who were either induced during the 39th week of pregnancy or assigned to no intervention.

Induction didn’t significantly reduce the rate of perinatal death — fetal death after 28 weeks or infant death in the first week of life — or severe complications in newborns. There were also 35 percent fewer diagnoses of hypertensive disorders among women in the induction group.

“I definitely think it settles the question that it’s a safe option,” said Greene.

About 18 percent of women in the induction group went on to have a C-section, compared to just over 22 percent in the control group. Women who had their labor induced did stay a median of six hours longer in the labor and delivery unit. But their overall time in the hospital was shorter, given the lower rate of C-sections.

The study’s recruitment of pregnant women offers a hint about how the idea of induction might be received more broadly, experts said. While 16,000 women declined a spot in the study, more than 6,000 signed up.

“It was surprising how many women were happy to be in the study,” said Dr. Mary Norton, an OB-GYN at the University of California, San Francisco, who wasn’t involved in the study. Norton and other obstetricians saw that as two sides of the same coin: Some women are excited about the option, but it’s not the right choice for everyone. Dr. William Grobman, an OB-GYN at Northwestern Medicine and the lead author of the study, agreed.

“It’s not saying this is the only thing to do. This is all about patient-centric care,” he said.

There are still lofty questions about how, exactly, the idea of induction at 39 weeks would work in practice. Will doctors actively offer it as an option to every patient, or will they simply no longer turn down requests for induction due to concerns about the risk of needing a C-section? What’s the best way to walk pregnant women through the potential risks and benefits of either choice?

Walker said there’s still a “very real concern” about over-medicalizing labor in healthy women who aren’t experiencing problems with their pregnancy. Labor can be induced with drugs that cause contractions or soften the cervix, or by rupturing the amniotic sac. But induction doesn’t always work. And in some cases, it can cause complications, such as excessive contractions.

“I don’t think my reaction as a clinician would be to start inducing everyone low-risk tomorrow,” she said. “But if a low-risk woman comes to me and asks for an induction, I’m no longer going to say it increases the risk of cesarean delivery.”

It’s also not clear whether the findings would translate to countries with different types of health systems. Walker said it’s critical to run a trial in the U.K., where she practices, before induction at 39 weeks becomes widespread.

“This trial may well mean a trial like that will now get funded in the U.K.,” Walker said.

There’s also concern that a broad shift toward elective inductions might strain limited resources in labor and delivery units, particularly in hospitals that are understaffed or already running at full capacity.

“Labor and delivery bed time is a very precious commodity, and very expensive,” said Greene. If demand for induced labor significantly increases, health facilities will have to come up with creative ways to free up more bed space, such as beginning the induction process outside the labor and delivery unit.

Experts also echoed the recommendations of ACOG and SMFM: It’s critical to make sure labor is only induced in women who are actually 39 weeks along, and no earlier.

“In the real world, there are going to be patients for which the dating is not as clear” as in the study, said Norton, who previously served as the president of the Society for Maternal-Fetal Medicine. But still, experts said, the study offers crucial evidence for women trying to navigate the deeply personal decisions around labor and delivery.

“My greatest wish as a researcher is to have good quality evidence to help women make the right decision for them and their families,” said Walker. This study, she said, gives women that kind of evidence.

This story has been updated with additional information about ACOG’s current guidance.