Inducing Labor at 39 Weeks Decreases Need for Cesarean Section

Inducing labor in healthy women at 39 weeks into their pregnancy reduces the need for cesarean section and is at least as safe for mother and baby as waiting for spontaneous labor. Choosing to induce could also reduce the risk that mothers will develop preeclampsia and that newborns will need respiratory support after delivery, according to a study publishing online in the New England Journal of Medicine on August 8.

The findings are in contrast to a widely held perception that health care providers should avoid inducing labor in first-time mothers.

“This doesn’t mean that everyone should be induced at 39 weeks,” says the study’s co-author Robert Silver, chair of obstetrics and gynecology at University of Utah Health and a maternal-fetal medicine physician at Intermountain Healthcare in Salt Lake City. Kim Hall, a research nurse coordinator at U of U Health and Intermountain Healthcare, is also co-author on the study.

“Electing to induce labor is a reasonable option that may give the best chance for vaginal delivery and improve outcomes,” says Silver.

Results were from 6,106 first-time mothers enrolled into the randomized ARRIVE clinical trial carried out at 41 hospitals participating in the National Institutes of Health-supported Maternal Fetal Medicine Units Network. More than 1,200 women were at the Utah MFMUN, consisting of University Hospital and Intermountain Medical Center, the largest enrolling site in the trial.

A rising C-section rate

Driving the study is a steadily increasing rate of babies being delivered by C-section in the U.S., a number that has been holding at 32 percent since 2016. Medically unnecessary cesarean deliveries in healthy first-time mothers account for 80 percent of those deliveries, a point of concern.

Although the procedure is generally safe, the major surgery increases risk for complications to both mother and baby, and to future pregnancies. Women who deliver by C-section once are more likely to continue delivering that way, increasing the likelihood of high-risk complications such as placenta accreta.

For years, health care providers had been taught to avoid inducing labor in healthy, first-time mothers based on the belief that inducing increases the chance for C-section births. However, recent results from small, observational studies indicated that this may not necessarily be the case.

ARRIVE was a prospective trial designed to test this premise by examining outcomes from two groups of healthy, first-time mothers. One group elected to induce labor at 39 weeks, when the baby is full term and it is considered safe for mothers to give birth. The other group took part in expectant management or “watchful waiting,” the routine practice of waiting for spontaneous labor but undergoing active intervention should a medical need arise.

Inducing labor vs. waiting

On average, women who chose to induce at 39 weeks delivered nearly one week earlier than women who waited for spontaneous labor. C-section delivery was significantly less likely after elective induction than after expectant management (18.6 vs. 22.2 percent).

Based on these data, the researchers estimate that inducing labor at 39 weeks could eliminate the need for 1 C-section for every 28 deliveries.

“We’re always trying to find the safest way to deliver babies and take care of our patients,” says M. Sean Esplin, an associate professor of obstetrics and gynecology at U of U Health and chief of maternal-fetal medicine at Intermountain Healthcare. “If the primary goal is to keep rates of C-sections down, then elective induction is an option.”

Choosing to induce labor at 39 weeks is at least as safe as spontaneous labor, according to results from the study. A composite score measuring several health indicators in newborns — including death, seizures, hemorrhage and trauma — was not significantly different between the two groups.

Inducing labor was linked to significant improvement in two specific outcomes: women were less likely to develop preeclampsia (9 vs. 14 percent), and rates of respiratory distress decreased in newborns. Silver says that the placenta tends not to function as well later in pregnancy, possibly explaining why mothers and babies who deliver earlier may fare better.

The study’s findings held true regardless of the woman’s age, ethnicity and BMI. Currently, researchers are evaluating whether inducing delivery at 39 weeks is cost effective.

“These results open the door for pregnant women and their health care providers to talk about what the woman wants to do,” says Michael Varner, vice chair for research in obstetrics and gynecology at U of U Health and primary investigator of the Utah MFMUN.

“The opinions that matter most comes from the women we serve,” says Varner.

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This research was supported by the National Institutes of Health and publishes online as “Labor Induction versus Expectant Management in Low-Risk Nulliparous Women” in the New England Journal of Medicine on August 8, 2018.