Elective Labor Induction at 39 Weeks of Gestation Compared With Expectant Management: Factors Associated With Adverse Outcomes in Low-Risk Nulliparous Women

Abstract

Objective: To evaluate characteristics associated with adverse outcomes in low-risk nulliparous women randomized to elective labor induction at 39 weeks of gestation or expectant management.

Methods: We conducted a secondary analysis of women randomized during the 38th week to induction at 39 weeks of gestation or expectant management. Deliveries before 39 weeks of gestation and those not adherent to study protocol or with fetal anomalies were excluded. A composite of adverse outcomes (perinatal death or severe neonatal complications), third- or fourth-degree lacerations, and postpartum hemorrhage were evaluated. Log binomial regression models estimated relative risks and 95% CIs for associations of outcomes with patient characteristics including randomly assigned treatment group. Interactions between patient characteristics and treatment group were tested.

Results: Of 6,096 women with outcome data, 5,007 (82.1%) met criteria for inclusion in this analysis. Frequency of the perinatal composite was 252 (5.0%), 166 (3.3%) for third- or fourth-degree perineal laceration, and 237 (4.7%) for postpartum hemorrhage. In multivariable analysis, intended labor induction at 39 weeks of gestation was associated with a reduced perinatal composite outcome (4.1% vs 6.0%; adjusted relative risk [aRR] 0.71; 95% CI 0.55-0.90), whereas increasing body mass index (BMI) was associated with an increased perinatal composite outcome (aRR 1.04/unit increase; 95% CI 1.02-1.05). Decreased risk of third- or fourth-degree perineal laceration was observed with increasing BMI (aRR 0.96/unit increase; 95% CI 0.93-0.98) and in Black women compared with White women (1.2% vs 3.9%; aRR 0.34; 95% CI 0.19-0.60). Increased risk of postpartum hemorrhage was observed in Hispanic women compared with White women (6.3% vs 4.0%; aRR 1.64; 95% CI 1.18-2.29). Patient characteristics associated with adverse outcomes were similar between treatment groups (P for interaction >.05).

Conclusion: Compared with expectant management, intended induction at 39 weeks of gestation was associated with reduced risk of adverse perinatal outcome. Patient characteristics associated with adverse outcomes were few and similar between groups.

Clinical trial registration: ClinicalTrials.gov, NCT01990612.

Conflict of interest statement

Financial Disclosure

Robert M. Silver disclosed receiving funds as a consultant for Gestavision. Gail Mallett reports that money was paid to her institution from the George Washington University Biostatistics Center. Edward K. Chien disclosed that money was paid to his institution from Alydia Health and Gestvision. Both were industry sponsored research projects without overlap with this study. Ronald S. Gibbs disclosed that money was paid to him from Gestavision for consultation and ACI/Novavax for serving on the DSMB for a clinical trial of RSV vaccine. Geeta K. Swamy received funds from GlaxoSmithKline, Pfizer, and SAOL. The other authors did not report any potential conflicts of interest.

Figures

Figure 1.

Flowchart of eligibility determination for inclusion in this secondary analysis. *Onset defined as when the process of delivery started. †Women assigned to induction were excluded if their delivery began after 39 0/4 weeks of gestation unless the delay was due to a newly developed medical indication (eg, awaiting resolution of active herpes) and women assigned to expectant management were excluded if an induction without a medical indication was initiated before 40 5/7 weeks of gestation. Women in either group were excluded if they had an elective cesarean delivery without labor. ‡Among those in the intended induction group who achieved 39 weeks of gestation with a nonanomalous fetus (n=2,505), delivery per protocol included electively induced labor (n=2,150), spontaneous labor (n=285), or medically indicated delivery (n=65) from 39 0/7 to 39 4/7 weeks of gestation, or delivery delayed past 39 4/7 weeks of gestation because of a newly developed medical indication (ie, active herpes) (n=5). Among those in the intended expectant management group who achieved 39 weeks of gestation with a nonanomalous fetus (n=2,502), delivery per protocol included induction from 40 5/7 to 42 2/7 weeks of gestation (n=440), or spontaneous labor (n=1,552), or medically indicated delivery (n=510) from 39 0/7 to 42 2/7 weeks of gestation.