Induction at 39 Weeks: Fewer C-Sections Than Watchful Waiting

Tara Haelle

August 08, 2018

Inducing labor at 39 weeks in low-risk, nulliparous women appears at least as safe for mother and baby as waiting for spontaneous labor, and to boot, results in a lower cesarean section rate, according to the newly published, prospective randomized ARRIVE trial, which was published online August 9 in the New England Journal of Medicine.

The study also found lower rates of pre-eclampsia and newborn respiratory distress among those who were induced.

"Our data suggest that one cesarean...may be avoided for every 28 deliveries among low-risk nulliparous women who plan to undergo elective induction of labor at 39 weeks," write William Grobman, MD, professor of obstetrics and gynecology at Northwestern University Feinberg School of Medicine in Chicago, Illinois, and colleagues.

The ARRIVE trial's preliminary findings created a stir when they were released earlier this year at the Society for Maternal-Fetal Medicine's 38th Annual Pregnancy Meeting, as covered by Medscape Medical News, and prompted further debate at the American College of Obstetricians and Gynecologists (ACOG) meeting in May.

Now published, "These findings contradict the conclusions of multiple observational studies that have suggested that labor induction is associated with an increased risk of adverse maternal and perinatal outcomes," say Grobman and colleagues, noting that those studies compared women who had induced labor with those who had spontaneous labor, instead of expectant management.

"Electing to induce labor is a reasonable option that may give the best chance for vaginal delivery and improve outcomes," says study coauthor Robert Silver, MD, chair of obstetrics and gynecology at University of Utah Health, Salt Lake City, in a press release by his institution. He adds, however, that "this doesn't mean that everyone should be induced at 39 weeks."

ARRIVE Data Are Finally Published

The multicenter ARRIVE study involved 6106 women who were randomly assigned in their 38th gestational week to induction or expectant management at 39 weeks, 0 to 4 days. The women, from 41 hospitals across the United States, were nulliparous with a live singleton fetus in vertex position in an uncomplicated pregnancy and without contraindications for a vaginal delivery.

The only significant difference between the groups at baseline was that more women assigned to expectant management had a past pregnancy loss (25.6%) than women in the induction group (22.8%). Most of the women (94%) had a physician provider and 6% had a midwife. 

Of the 3062 women assigned to induction, 18.6% underwent a cesarean delivery. Of the 3044 assigned to expectant management, 22.2% had a C-section, translating to a 16% reduced risk of a cesarean delivery with induction at 39 weeks (P < .001).

The primary outcome, a composite of perinatal death or severe neonatal complications, occurred in 4.3% of the newborns whose mothers were induced and in 5.4% of mothers who were expectantly managed (P = .049).

The relative risk of death or severe complications was 20% lower for newborns in the induction group, even after adjustment for mothers' previous pregnancy loss. Newborns in the induction group also spent less time in hospital and required less respiratory support.

And only 9.1% of women in the induction group developed a hypertensive disorder of pregnancy compared with 14.1% of those in the expectant management group (P < .001).

Women in the induction group also reported slightly less pain and slightly more perceived control while giving birth than women who underwent "watchful waiting." Although women in the induction group spent more time on average in labor and delivery, their postpartum stays were shorter than the expectant management group. There were no other significant differences in maternal outcomes.

Applying Results Could Cause Chaos: Women and Physicians Must Decide

ACOG guidelines currently state that elective induction may be considered much later than 39 weeks — at 41 weeks — and should be performed at 42 weeks. However, mounting evidence consistent with the new ARRIVE findings is pushing the field toward greater acceptance of elective induction at 39 weeks.

In a session at the ACOG annual conference in May, led by Aaron Caughey, MD, PhD, chair, department of obstetrics and gynecology, Oregon Health & Science University, Portland, discussion of the ARRIVE findings continue, as reported by Medscape Medical News.

At the time, Caughey urged caution when interpreting the ARRIVE data, remarking that it could cause "chaos and mayhem" to suggest to all women that induction at 39 weeks might be safest for the baby.

Whether an institution may get the same results as the ARRIVE trial would depend on the practice setting, caseload, department culture, and many other factors he said.

The ARRIVE authors say their newly published data at least give women more options.

"This new knowledge gives women the autonomy and ability to make more informed choices regarding their pregnancy that better fit with their wishes and beliefs," Grobman says. "Induction at 39 weeks should not be routine for every woman, but it's important to talk with their provider and decide if they want to be induced and when."

The study was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Grobman has reported no disclosures. Disclosures for the other authors are listed in the article.

N Engl J Med. 2018;379:513-523. Abstract

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