Release of results from the ARRIVE trial has provided answers to some concerns about 39-week induction while leading to some questions about the participants and the implication of the findings for clinical practice. The data and an accompanying editorial were published in The New England Journal of Medicine.
Led by investigators from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the trial was conducted at 41 US obstetrical centers. The objective was to assess the impact of induction at 39 weeks versus expectant management in low-risk nulliparas. The primary outcome was a composite of perinatal death or severe neonatal complications; the principal secondary outcome was cesarean delivery.
For the study, 3062 women were randomized to labor induction at 39 weeks 0 days to 39 weeks 4 days and 3044 were randomized to expectant management. All of the participants were low-risk nulliparas who at the time of randomization were at 38 weeks 0 days to 38 weeks 6 days’ gestation. Of the participants, 63% had a modified Bishop score < 5 at randomization. Both groups were similar but fewer women in the induction group had a previous pregnancy loss (22.8% vs 25.6%; P= 0.001).
Cesarean delivery was significantly less likely in the induction group than in the expectant management group (18.6% vs 22.2%; relative risk [RR], 0.84; 95% CI, 0.76 to 0.93; P< 0.001) and it was not materially affected by adjustment for a history of pregnancy loss. Hypertensive disorders also were significantly less likely in women randomized to induction (9.1% vs. 14.1%; RR, 0.64; 95% CI, 0.56 to 0.74; P< 0.001). Less pain on a 10-point Likert scale and more perceived control during childbirth were reported by the women in the induction arm, and while they had shorter postpartum hospital stays, they spent less time on labor and delivery.
The primary perinatal come occurred in 4.3% of neonates in the induction group and in 5.4% in the expectant management group (RR, 0.80; 95% CI 0.64 to 1.00; P= 0.049). “Labor induction,” the authors said, “is probably not associated with a higher risk of adverse perinatal outcomes than expectant management and it may be associated with as much as a 36% lower risk than expectant management.”
Subgroup analyses showed that the maternal and perinatal results were not significantly affected by race, ethnic group, maternal age, body mass index, or modified Bishop score nor by type of admitting provider. (In 94% of cases, the provider was a physician and in 6%, it was a midwife.)
The authors said their data suggest that “1 cesarean delivery may be avoided for every 28 deliveries among low-risk nulliparous women who plan to undergo elective induction of labor at 39 weeks.” Given the size of the ARRIVE trial, they said it had the ability to detect differences that may not have been discerned in previous trials. However, most of the individual perinatal outcomes are infrequently seen and the trial was not powered to detect differences in them. It is also not clear whether the results are broadly generalizable. The researchers noted that more studies are needed to determine whether labor induction at 39 weeks in low-risk nulliparas is cost-effective.
In an accompanying editorial, Dr. Michael Greene said that other unanswered questions include why more than 16,000 women eligible for the trial declined to participate and how obstetrical centers across the country would accommodate longer lengths of stay on labor and delivery if the idea of induction at 39 weeks has a wide appeal to women. He said, however, that the results “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.”