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New study suggests induced labor at 39 weeks may reduce C-section risk

POSTED: February 18, 2018 11:12 a.m.
Jennifer Graham/

Current guidelines warn doctors not to induce labor before the 40th week of pregnancy because of an increased risk of C-sections. But a study presented last week upends the conventional wisdom. Health women who were induced at 39 weeks had a lower risk of a surgical delivery and their babies were less likely to need help breathing in the first few days of life, researchers at The National Institutes of Health found.

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New research could shrink the length of pregnancy from 40 to 39 weeks for healthy, first-time mothers who choose to have labor induced.

In a nationwide study of 6,100 women, more than 1,200 of them in Utah, researchers found that women whose labor was induced at 39 weeks had fewer cesarean sections than those who went into labor spontaneously or who were induced at 40 weeks or later. The babies delivered a week earlier also had slightly fewer incidences of respiratory distress after birth.

The findings, presented at a recent conference in Dallas, upend current thinking, which is that induction at 39 weeks should be discouraged because it increases the risk of a woman needing to have a surgical birth.

While no women should be induced before 39 weeks unless there are medical problems that require an early delivery, the study relieves concern about induction after that point, said Dr. Sean Esplin, a high-risk pregnancy specialist at the Intermountain Maternal Fetal Medicine Program at Intermountain Medical Center.

“Thirty-nine weeks is the optimal time. Almost all babies — 99.9 percent — are mature at that point, and they don’t really gain anything from continuing. What we’re really doing is waiting for the mother’s cervix and uterus to begin the process of going into labor, and sometimes that doesn’t happen,” Esplin said.

“Every week that goes by, your chance of having a cesarean section actually goes up, and complications for the baby may also go up. So this study was landmark in the sense that it changes the way we’re thinking about the induction of labor,” he said.

What researchers found

The study was funded by the National Institutes of Health and involved women at 14 sites across the country, including Intermountain Healthcare and the University of Utah. The full report has not yet been published, but its findings were presented Feb. 1 at the annual meeting of the Society for Maternal-Fetal Medicine in Dallas.

Women who participated had to be pregnant with their first child and have no health problems. They were divided into two groups — those who agreed to be induced at 39 weeks, and those who agreed to wait for spontaneous labor or, if necessary, to be induced after 40 weeks.

Of women who were induced at 39 weeks, 19 percent had C-sections, compared with 22 percent of the other women. The induced group also had better outcomes in other measures of health. Nine percent of women induced at 39 weeks experienced pre-eclampsia and gestational hypertension, compared with 14 percent of the other women.

As for the babies, 3 percent of those born to mothers induced at 39 weeks needed help breathing, compared with 4 percent of those born to other women.

While those numbers are too small to say the study proves the babies of women induced at 39 weeks are better off, it's also not a finding that should be dismissed, said Dr. Robert Silver, an OB-GYN and the lead investigator at the University of Utah. "It's almost certain to help on a population level," Silver said.

Researchers also looked at other facets of delivery, such as how long both groups of women were in labor. But those numbers are still being analyzed and won't be made public until the study is published in a peer-reviewed journal, he said.

The optimal number?

This isn’t the first time guidelines for induction have changed.

Dr. Uma Reddy, a maternal-fetal medicine specialist for the National Institutes of Health, said doctors used to let women go to 42 weeks before inducing labor, but guidelines were later changed to 41 weeks after research found better outcomes for mother and baby.

Although doctors have known that 39 weeks is the best time for delivery, they've been taught that inducing then could result in a C-section, which is major surgery for the mother and is associated with worse health outcomes for the baby. (Utah has the lowest C-section rate in the country, according to the Centers for Disease Control and Prevention.)

Babies delivered by C-section sometimes suffer respiratory distress, and they miss out on the benefits of passing through the birth canal, such as receiving beneficial microbes from their mother. But waiting can be risky as well.

“If you go beyond 39 weeks, the risks for mothers and babies increase. Women can develop pre-eclampsia, the placenta might not work as well, you could have problems with fluid and the fetal heart rate; you could have a stillbirth occur,” Reddy said.

Rebecca Dekker, a registered nurse who has a doctorate in nursing and founded the website Evidence Based Birth, said she is waiting for the full report to be published in a peer-reviewed journal before drawing any conclusions.

From what was presented in Dallas, Dekker said the study appeared to be comprehensive and well-managed, but she said the findings are only applicable to women who want a “medicalized” birth attended by physicians, not a birth experience at home or in a birthing center with midwives or doulas.

“Also, there are a lot of things that women who don’t want a medicalized birth can do that will lower their risk of cesarean much more than an induction would,” she said in a podcast about the report.

For example, one study found that walking around during the early stages of labor, instead of laboring in bed, lowered the C-section rate from 16 percent to 5 percent, she said. “Walking is free, easy and noninvasive. Inductions are quite the opposite,” Dekker said.

Silver, at the University of Utah, said that about 25 to 30 percent of women who were asked to participate in the study agreed, and he acknowledged some inherent bias in the findings: "People who are opposed to inductions wouldn't have chosen to be in the study in the first place."

He also said, “If women feel strongly about not wanting to be induced, they shouldn’t be anxious about going to 40 weeks or 41 weeks.” The chance of stillbirth and other serious complications in an otherwise healthy pregnancy is low, even if women choose to wait, Silver said.

“We’re not recommending that everyone deliver at 39 weeks; we’re saying it’s a reasonable option for some people," he said.

In the coming year, doctors will be evaluating how the study will change the way they practice and whether inducing at 39 weeks is more cost-effective than waiting, Intermountain's Esplin said.
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