Cesarean delivery after non‐medically indicated induction of labor: A population‐based study using different definitions of expectant management

Abstract

Introduction Most observational studies found that non‐medically indicated induction of labor (IOL) is not associated with an increased risk of cesarean delivery compared with expectant management, defined as all births at a later gestation. However, given the higher rate of cesarean delivery at late term, this definition of the expectant management group might bias the results of observational studies in favor of IOL at early or full term when estimating the risk of short‐term (eg up to 1 week) expectant management. Material and methods We conducted a retrospective cohort study including 447 066 singleton term and post‐term hospital births that occurred in Austria between 2008 and 2016. Multivariate logistic regression was used to test the association of IOL and cesarean delivery at each week of gestation from 37‐41. Expectant management was either defined as all births at “next week or beyond” or “at next week”. Results Non‐medically indicated IOL was associated with increased odds for cesarean delivery at 37 and 38 weeks, and reduced odds at 40 and 41 weeks. At 39 weeks, IOL resulted in comparable cesarean rates compared with expectant management defined as “next week or beyond” (17.2% vs 16.2%; adjusted odds ratio [OR] 0.93; 95% confidence interval [CI] 0.86‐1.00; P = .059). However, when defined as births “at the next week”, expectant management was associated with significantly reduced odds for cesarean delivery (13.6%; adjusted OR 0.76; 95% CI 0.70‐0.82; P < .001). Comparison of the cesarean delivery rates for the two definitions of expectant management showed that the “next week and beyond” model underestimates the benefit of short‐term expectant management by up to 1 week, particularly for IOL at weeks 38 and 39. Conclusions Our findings demonstrate that the definition of the expectant management group has a significant impact when analyzing the outcome of IOL in retrospective cohort studies. Non‐medically indicated IOL is not an all‐or‐none choice between “elective” induction and indefinite expectant management. Thus, to define the control group as all births at the next week could be useful for clinical decision‐making, as it allows to estimate the risks of expectant management until the next appointment compared with immediate IOL.

Induction of labor and cesarean section

“…Table 1 shows the rate of Cesarean section following induction of labor in several publications. This also includes data from the current manuscript by Zenzmeier et al 6 The Table shows that the rate of Cesarean section in nulliparous women is twice as high as that for all women, which is not surprising. The key finding is that the there is no indication of any influence of the week of gestation on the Cesarean section rate.…”

“…In this issue of AOGS, Zenzmier et al 6 explore the question using different definitions of expectant management. The authors argue that IOL for late term (42 +0 or more) pregnancies is associated with a very high rate of Cesarean section, and that elective IOL earlier (40 +0 weeks for example) may appear to have a lower Cesarean section rate compared to all those who are not induced at 40 +0 weeks (which include those at or beyond 42 +0 weeks with a very high C section rate).…”

“…This is true not only for all indications for IOL 3 but also for elective (for non-medical reasons) IOL. 4,5 In this issue of AOGS, Zenzmier et al 6 If we believe that a significantly lower Cesarean section rate can be achieved by delaying IOL by one week prior to 41 +0 weeks, one expects the success of induction of labor to steadily increase (or the rate of Cesarean section following IOL to progressively decrease) with increasing gestation from 37 +0 weeks till 41 +0 weeks. In other words, one would think that the further one is away before the due date, less successful would IOL be.…”

Comparison of Maternal Labor-Related Complications and Neonatal Outcomes Following Elective Induction of Labor at 39 Weeks of Gestation vs Expectant Management

“…gestation. There were 12 retrospective cohort studies, 20,21,[24][25][26][28][29][30][31][32][33][34] 1 cross-sectional study, 27 and 1 randomized clinical trial 10 (Table 1).…”

“…There were no differences between groups in the likelihood of operative vaginal birth (OR, 1.01 [95% CI, 0.84-1.21]), postpartum hemorrhage (OR, 0.93 [95% CI, 0.66-1.32]), or low 5-minute Apgar score (OR, 0.86 [95% CI, 0.53-1.38]) (Table3).Among nulliparous women only (n = 407 302), induction at 39 weeks of gestation (n = 31 947) was associated with a decreased likelihood of emergency cesarean section (9 studies10,20,[24][25][26][27]29,32,34 ; OR, 0.80 [95% CI, 0.70-0.91]) and NICU admission (5 studies10,20,24,29,32 ; OR, 0.75 [95% CI, 0.63-0.89]). There was no difference between groups in terms of third-or fourthdegree perineal injury (OR, 0.97 [95% CI, 0.85-1.10]), operative vaginal birth (OR, 1.11 [95% CI,…”