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Caughey AB, Sundaram V, Kaimal AJ, et al. Maternal and Neonatal Outcomes of Elective Induction of Labor. Rockville (MD): Agency for Healthcare Research and Quality (US); 2009 Mar. (Evidence Reports/Technology Assessments, No. 176.)

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Maternal and Neonatal Outcomes of Elective Induction of Labor.

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Executive Summary

Introduction

Induction of labor is increasing in the U.S. The overall induction rate has increased from 9.5 percent in 1990 to 22.1 percent in 2004. Induction of labor that is not indicated for a medical reason, also termed elective induction of labor, appears to be rising as well and at a rate even more rapidly than that of the overall induction of labor. Elective induction may be motivated by a variety of reasons. For example, pregnant women may wish to end their pregnancy because of physical discomfort, concern for rapidly progressing labor precluding timely arrival at the hospital or epidural placement, scheduling issues, or ongoing concerns for maternal, fetal, or neonatal complications. Clinicians who care for pregnant women (e.g., obstetricians, family-practice physicians, midwives) may have similar non-medical reasons for choosing elective induction of labor for their patients. They, too, may wish to end their patients' physical discomfort or have concerns about either distance from the hospital or ongoing risk in the pregnancy. However, clinicians may also be incentivized to utilize elective induction for their own financial benefit and scheduling preferences. Thus, it is imperative to determine the potential outcomes associated with elective induction of labor.

Elective induction of labor necessarily reduces some risks of an ongoing pregnancy. Such risks include developing preeclampsia, oligohydramnios, macrosomia, or intrauterine fetal demise at a later gestational age. However, the commonly held dogma regarding induction of labor is that it increases the risk of cesarean delivery, which in turn is associated with a host of maternal complications. Additionally, a cesarean delivery in the current pregnancy increases both maternal and neonatal risks in future pregnancies. Thus, determining the effect of elective induction of labor on cesarean delivery as well as other maternal and neonatal outcomes is important.

When evaluating the risks and benefits of elective induction of labor, it is essential that women having elective induction of labor be compared to women having expectant management of labor. Expectant management of the pregnancy involves nonintervention at any particular point in time and allowing the pregnancy to progress to a future gestational age. Thus, the woman undergoing expectant management may go into spontaneous labor or may require indicated induction of labor at a future gestation due to developing preeclampsia, nonreassuring antenatal testing, or postterm pregnancy. One methodologic problem with many studies of induction of labor, particularly observational studies, is that they often use women in spontaneous labor as a control group. This is problematic because at any point in the term pregnancy the clinician has the choice between induction of labor and expectant management, not spontaneous labor. Since increasing gestational age itself is associated with cesarean delivery, these studies are fundamentally flawed and can lead to misleading conclusions.

Key Questions

With this background in mind, we sought to conduct a systematic review and decision analysis utilizing the existing literature in order to answer several questions regarding the effects of elective induction of labor. Specifically, we sought to answer the following Key Questions:

Key Question 1: What evidence describes the maternal risks of elective induction versus expectant management?

Key Question 2: What evidence describes the fetal/neonatal risks of elective induction versus expectant management?

Key Question 3: What is the evidence that certain physical conditions/patient characteristics (e.g., parity, cervical dilatation, previous pregnancy outcome) are predictive of a successful induction of labor?

Key Question 4: How is failed induction defined?

Systematic Review of Elective Induction of Labor

Methods

We searched MEDLINE® to identify English-language studies of induction of labor published from January 1966 to May 2007. We also manually reviewed the reference lists of included articles and bibliographies of systematic reviews of induced labor to identify relevant articles.

Inclusion criteria. We included randomized controlled trials (RCT), cohort and case-control studies that compared women who had undergone induced labor without a specific indication, prior to 42 0/7 weeks gestational age, with women who were either managed expectantly or had spontaneous labor. We defined elective induction as induction of labor at or after 37 0/7 weeks and prior to 42 0/7 weeks of gestation without a maternal or fetal indication. Elective induction of labor studies were included only if the article reported mode of delivery (cesarean, vaginal or operative), maternal or neonatal outcomes. We also included all induction of labor studies (irrespective of whether or not the induction was elective) if the article reported predictors of success or failure for induction. Multiple articles on the same population were included once in our analysis.

Data extraction. Two authors independently reviewed the title and abstract of each study to assess whether the article met inclusion criteria. Conflicts regarding data abstraction were resolved by re-review and discussion. From each included article, we extracted the following information: Study period, location and setting of study, whether or not the induction was elective, induction method, study design, definition of successful induction, inclusion and exclusion criteria (for elective induction of labor studies), mode of delivery, maternal and neonatal outcomes for all patients and stratified by parity (for elective induction of labor studies), predictors of failed induction (for all induction of labor studies) and quality assessment information.

Quality assessment. Consistent with the AHRQ draft Methods Guide for Conducting Comparative Effectiveness Reviews, we developed specific criteria for evaluating the quality of the individual included studies and for assessing the applicability of these studies to the Key Questions. We then graded the overall quality of the literature addressing each of the Key Questions. For our quality assessment, individual studies were evaluated with respect to study design, measurement of outcomes, sample size, and statistical analyses. These assessments were summarized as a good, fair, or poor rating for each individual study. We assessed the applicability of the individual studies to the Key Questions by evaluating the population studied, place and time the study was conducted, and methods of induction utilized. Individual applicability was assessed as good, fair, or poor. To grade the overall strength of evidence, we considered the quality and applicability of the individual studies, the consistency of the results across the included studies, and volume of the literature for each of the Key Questions. We assigned a grade of high, moderate, low, or insufficient to each of the items.

Data analysis. To evaluate the maternal and fetal/neonatal risks of elective induction versus expectant management, we computed two summary effect sizes for each outcome of interest that was reported in more than four studies using random effects models: A summary odds ratio and a summary risk difference. To minimize heterogeneity, we synthesized studies on the basis of study design. We assessed statistical heterogeneity for summary effects by calculating the Q statistic (considered Q statistics with p <0.05 as heterogeneous) and I2 statistic (considered I2 statistics greater than 50 percent as heterogeneous). We also performed sensitivity analyses to evaluate the robustness of our results and assessed our results for publication bias.

Systematic Review Results

We reviewed 3,722 articles of which 76 met inclusion criteria: 34 studies examined elective induction of labor and associated outcomes, including 11 RCTs which compared women with elective induction of labor to expectant management (nine studies) or spontaneous labor (two studies). We identified 42 observational studies of induction of labor and predictors of induction success (nearly all of which compared women who had elective induction of labor to women with spontaneous labor). We present our results below as responses to the Key Questions.

Key Question 1: What evidence describes the maternal risks of elective induction versus expectant management?

Cesarean delivery. Of the nine RCTs that compared cesarean delivery among women who had elective induction of labor with those with expectant management, the combined summary odds ratio slightly favored elective induction of labor. Expectant management of pregnancy was associated with an approximately 22 percent increase in cesarean delivery (OR=1.22; 95 percent CI 1.07–1.39, P=0.003) and an absolute risk difference of nearly two percent (95 percent CI: 0.2 percent to 4 percent, P=0.033). The majority of these studies were in women at or beyond 41 0/7 weeks of gestation (OR 1.21, 95 percent CI 1.01–1.46). Three trials reported no difference in risk of cesarean delivery among women who were induced at less than 41 0/7 weeks gestational age (OR 1.73, 95 percent CI: 0.67–4.5, P=0.26) but all of these trials were of poor quality, thus there is insufficient evidence to make conclusions as to outcomes before 41 0/7 weeks. Only three studies addressed whether parity affected the risk of cesarean delivery between expectant management and electively induced labor; these studies reported no difference in risk for nulliparas and there was insufficient information to draw any conclusions on the risk for multiparas. When we stratified the studies to those conducted in or prior to 1990 and those conducted after 1990, there was no statistically significant difference in the odds of cesarean delivery for either of the two groups. When we stratified the analysis by country, we found moderate evidence that the odds of cesarean delivery were higher in women who were expectantly managed compared to elective induction of labor in studies conducted outside the U.S. (OR 1.21; 95 percent CI 1.05–1.40) but were not different in studies conducted in the U.S. (OR 1.28; 95 percent CI 0.65–2.49). The observational studies reported a consistently lower risk of cesarean delivery among women who underwent spontaneous labor (six percent) compared with women who had an elective induction of labor (eight percent) with a statistically significant decrease when combined (OR 0.63; 95 percent CI: 0.49–0.79). The principal reason for this difference in findings between the two types of studies is likely the different control groups used by the included studies. Since the clinical scenario faced by practitioners is induction of labor now versus expectant management with either induction or spontaneous labor at a later date, gestational age is an important confounding factor, which may bias the estimate of effect on induction when induction is compared to spontaneous labor.

Operative vaginal delivery. An operative vaginal delivery consists of either a forceps- or vacuum-assisted vaginal delivery. Most of the six RCTs that examined the effect of elective induction of labor on operative vaginal delivery were small to medium-sized studies (only one study had 1700 women in each arm). There is moderate evidence that the odds of operative vaginal delivery were not statistically significantly different between women who were electively induced or expectantly managed (OR=0.91; 95 percent CI 0.79–1.04, P=0.18). Three RCTs reported no difference in the risk of operative vaginal delivery among women who were induced at less than 41 0/7 weeks gestational age (OR 0.71, 95 percent CI: 0.41–1.21, P=0.21), but all of these trials were of poor quality. For the seven observational studies, there was no significant difference in the risk of operative vaginal delivery between women in spontaneous labor compared to elective labor induction (OR=0.91; 95 percent CI 0.78–1.05, P=0.18). Although the observational studies involved more women, they were heterogeneous. Given the consistency of the findings in both RCTs and observational studies for a lack of difference in the risk of operative vaginal delivery, there is only moderate evidence regarding the relationship between elective induction of labor and operative vaginal delivery.

Length of labor. None of the included studies evaluated “prolonged labor” as a primary outcome. One RCT from Norway that included 508 women evaluated “prolonged first and second stages of labor” and found no statistically significant difference between women who were electively induced or expectantly managed. Four observational studies examined “mean duration of first and second stages of labor.” Only one of these studies that included 253 women in each group found a significant difference in the mean length of the first stage of labor in women who had elective induction of labor compared to spontaneous labor (6.0 versus 7.2 hours, respectively; P=0.008); the others reported no difference in length of labor. Given the limited evidence further information is needed to evaluate the effect of elective labor induction on the duration of labor. No studies reported or compared the median duration of labor. Thus, there is insufficient evidence addressing length of labor and elective induction of labor.

Maternal infections. Six studies (three RCTs and three observational) reported presence or absence of maternal infection; however, none provided detailed quantitative data such as risk ratios or risk differences. Four studies (two RCTs, two observational) provided some evidence that elective induction was not associated with an increased risk of chorioamnionitis and two observational studies provided some evidence that elective induction was not associated with an increased risk of endomyometritis. Thus, given the consistency in these findings, but the modest amount of available data, there is low quality evidence regarding the association of maternal infections and elective induction of labor.

Maternal blood loss and hemorrhage. Four studies (one RCT and three observational) evaluated the association between elective induction and postpartum hemorrhage and found no association. However, these studies likely lacked adequate statistical power to detect a difference. One RCT examined rates of blood transfusion between elective induction (2/265 [0.75 percent]) versus expectant management (3/175 [1.7 percent]) and found no statistically significant difference. No studies reported mean estimated blood loss as an outcome of interest. Thus, given the minimal amount of data and the lack of statistical power to examine this question, there is insufficient evidence to assess the assocation of maternal blood loss and elective induction of labor.

Key Question 2: What evidence describes the fetal/neonatal risks of elective induction versus expectant management?

Meconium stained amniotic fluid. There were six RCTs with a total of 5,478 women that examined whether the presence of meconium-stained amniotic fluid was associated with elective induction of labor. Women who were expectantly managed were more likely to have meconium stained amniotic fluid than those electively induced (OR 2.04; 95 percent CI 1.34–3.09). However, a high degree of heterogeneity existed among these studies. Only one randomized controlled trial evaluated this outcome among women who were induced at less than 41 0/7 weeks gestation and found a lower risk for the presence of meconium among women who were electively induced. Given the consistency of the findings and the quality of the individual studies, which ranged from poor to good, there is moderate evidence regarding the increased presence of meconium with elective induction of labor.

Meconium aspiration syndrome. Five RCTs, which ranged in size from 300 to 3000 participants and were of poor to good quality, provided somewhat conflicting results regarding the effect of elective induction on meconium aspiration syndrome. While two of the studies found higher rates of meconium aspiration in the setting of expectant management, these differences were not quite statistically significant and the other three studies found no difference. Overall, there was no difference in the risk of meconium aspiration syndrome to neonates between the two groups of women (OR 1.39; 95 percent CI 0.71–2.72). Thus, there are insufficient data to fully characterize the presence and strength of this association

Apgar score less than 7 at 5 minutes. Thirteen studies (four RCTs and nine observational) provided some evidence that the rate of 5-minute Apgar score less than 7 was no different between women with elective induction of labor compared to expectant management/spontaneous labor. The summary odds ratio from the RCTs was 1.18 (95 percent CI: 0.67–2.06). None of the RCTs reported this outcome among women who were induced at less than 41 0/7 weeks gestation. Given the relatively wide confidence interval, the fact that this outcome is relatively uncommon and maybe lacking adequate power, and the individual quality ratings of the studies, the overall evidence regarding this outcome was rated as low.

Umbilical arterial pH and umbilical arterial base excess. One good and one fair RCT provided evidence that elective induction of labor was not associated with higher rates of neonatal acidemia as measured by umbilical cord gases indicated by umbilical arterial pH (<7.0 or <7.1) and umbilical arterial base excess (<-12). However, there is insufficient evidence to draw conclusions about this a relatively uncommon outcome.

Fetal distress. While two poor-quality, small observational studies reported no difference in rates of fetal distress, one large, good-quality, RCT reported lower rates of fetal distress favoring elective induction of labor. Given the disagreement between the study findings, there is insufficient evidence to describe the association of elective induction of labor and fetal distress.

Respiratory distress syndrome. There is insufficient evidence from one poor quality large cohort study involving 4,472 women that did not observe any cases of respiratory distress syndrome in either group.

Transient tachypnea of the newborn. There is low quality evidence from three fair to good quality RCTs that the risk of transient tachypnea of the newborn was not different in women who had elective induction as compared to expectant management.

Neonatal sepsis. Two good quality, large RCTs examined both the risk of suspected neonatal sepsis and culture-proven sepsis. These two studies did not find that the rates of suspected neonatal sepsis were different in women with elective induction versus expectant management. Given the consistency of these two RCTs, the evidence was rated as low.

Hypoxic-ischemic encephalopathy. No studies designated hypoxic-ischemic encephalopathy as an outcome of interest and the evidence was rated as insufficient.

Birthweight. One RCT involving 302 women reported that the rate of large-for-gestational-age (LGA) neonates was lower in women who were electively induced compared to expectant management. However, three poor quality observational studies provided conflicting results regarding the effect of elective induction of labor on rates of birthweight greater than 4,000 grams.

Three fair to good quality RCTs provided evidence that elective induction of labor reduces the rate of macrosomia (birthweight greater than 4,500 grams). Four observational studies provided conflicting data regarding the effect of elective induction on incidence of birthweight less than 2,500 grams. There is low overall evidence that elective induction of labor reduces LGA and macrosomia.

Neonatal seizures. The two RCTs provided low quality evidence that there is no difference in the risk of neonatal seizure between women who were electively induced or expectantly managed.

Hypoglycemia. The two RCTs (one large and good quality and one medium sized and fair quality) provided low quality evidence that hypoglycemia was not associated with elective induction of labor.

Neonatal jaundice. The tree poor to fair quality studies (two small RCTs and one larger observational case-control) provided low-quality evidence that the risk of neonatal jaundice was not higher in women undergoing elective induction of labor.

Neonatal polycythemia. The two relatively large RCTs provided low-quality evidence that the risk of neonatal polycythemia was not different between women undergoing elective induction of labor compared to those who are managed expectantly.

Breastfeeding. One relatively small, poor quality, cohort study from the Netherlands provided insufficient evidence of higher rates of breastfeeding in women who had spontaneous labor than those who had induction of labor.

Key Question 3: What is the evidence that certain physical conditions/patient characteristics are predictive of a successful induction of labor?

Whereas the focus of our analysis for the preceding Key Questions focused on the comparative effectiveness of elective induction of labor and expectant management, for this Key Question we included studies of women undergoing induction of labor and also included those that used women in spontaneous labor as the control group as we were only examining the women who were induced.

Parity. Twenty-three studies examined parity as a predictor of cesarean delivery in women undergoing induction of labor. In three RCTs, there was a decreased risk of cesarean delivery among the multiparous women when compared with the nulliparous women (OR 0.21; 95 percent CI: 0.06–0.72). Among the 20 cohort studies, the rate of cesarean delivery was 28 percent among the nulliparous women compared with 10 percent among the multiparous women. When we combined the cohort studies, there was a decreased risk of cesarean delivery among the multiparous women when compared to the nulliparous women (OR 0.27; 95 percent CI 0.16–0.45). Thus, there is high-quality evidence of a decreased risk of cesarean delivery among multiparous women undergoing induction of labor compared with nulliparous women.

Cervical status. Twelve observational studies measured Bishop scores to evaluate cervical status as a predictor of cesarean delivery in women undergoing induction of labor. These studies differed by study design and patient population; however, all reported that the frequency of cesarean delivery was inversely related to Bishop scores such that a higher rate of cesarean delivery was observed in women with a lower Bishop score compared to women with more favorable cervix as represented by higher Bishop scores. Thus, there is moderate evidence that Bishop score is a predictor of cesarean delivery among women undergoing elective induction of labor.

Maternal age. Two observational studies presented conflicting data to support maternal age as a predictor of cesarean delivery in the setting of induction of labor. Thus, the direction of effect could not be adequately determined based on the current literature reviewed and the evidence was rated as insufficient.

Maternal body-mass index. We identified one small prospective cohort study that examined maternal body-mass index as a predictor of cesarean delivery in the setting of induction of labor. The authors found that women with a BMI greater than or equal to 30kg/m2 had a higher frequency of cesarean delivery. We rated the strength of evidence as insufficient given the small-sized, single study of the topic.

Gestational age. Four cohort studies had consistent evidence to provide moderate-quality evidence that increasing gestational age was associated with increased rates of cesarean delivery in the setting of induction of labor.

Amniotic fluid index. Three studies presented conflicting results regarding the level of amniotic fluid index at time of induction of labor and its effect on mode of delivery. The evidence was insufficient to support any conclusions regarding the direction of effect.

Key Question 4: How is failed induction defined?

We abstracted the definition of a successful labor induction from our included studies (n=76). While a majority of studies specifically defined successful labor induction, most of them defined failure in terms of mode of delivery (Table A). Just over half the studies (58 percent) defined success as achieving a vaginal delivery anytime after the onset of the induction of labor; in these instances, induction was considered a failure when it led to a cesarean delivery. Other definitions of success included a spontaneous vaginal delivery or achieving a vaginal delivery in a specified amount of time, most commonly 24 hours (but also 6, 12, or 18 hours). One study defined induction of labor success as the onset of labor within 12 hours. Only one study defined induction of labor success as achieving active labor.

Table ADefinition of induction of labor success

Definitionn/N (%)
Vaginal delivery44/76 (57.9%)144
Spontaneous vaginal delivery16/76 (21.1%)11, 15, 22, 25, 27, 28, 31, 43, 4552
Vaginal delivery within 24 hours9/76 (11.8%)1, 5, 13, 5358
Not Specified17/76 (22.4%)5975
Miscellaneous Definitions Used:
 Vaginal delivery within 6 hours
 Vaginal delivery within 12 hours
 Vaginal delivery within 18 hours
 Labor within 12 hours
 Active Labor Achieved
 Delivery within 48 hours of scheduled Induction

1/76 (1.3 %) 76
1/76 (1.3 %) 24
1/76 (1.3 %) 13
1/76 (1.3 %) 41
1/76 (1.3 %) 44
1/76 (1.3 %) 25

Note: Fourteen studies report more than one measure of induction of labor success.1, 5, 11, 13, 15, 22, 24, 25, 27, 28, 31, 41, 43, 44

Decision Analytic Model of Elective Induction of Labor

While the clinical constraints of the obstetric population limit the number of management options that can be investigated in a prospective fashion, decision analysis and cost-effectiveness analysis have been used to model the impact of induction strategies on clinical outcomes or cost in certain populations.77, 78 We constructed decision analytic models in order to identify aspects of elective induction of labor that warrant further investigation in future prospective studies. These models were specifically stratified at 39, 40, and 41 weeks of gestation and compared elective induction of labor to expectant management of the pregnancy.

Methods. To address the question of the consequences of induction of labor, and specifically examine what particular outcomes may drive this clinical situation, decision trees were constructed to simulate clinical scenarios in which elective induction of labor might be considered as an alternative to expectant management of the pregnancy. Since medical comorbidities of pregnant women may lead to an indicated induction of labor at any gestational age, the hypothetical cohort entering the decision tree consisted of women with low risk, singleton, vertex gestations. In addition, since nulliparous women tend to incur increased costs during labor, and have a higher likelihood of cesarean delivery in comparison to multiparous patients, in order to provide the most conservative estimate of the consequences of induction of labor, all patients were considered to have the increased risks associated with nulliparity.

Induction of labor for postterm pregnancy is one of the current recommended strategies by the American College of Obstetricians and Gynecologists at 42 0/7 weeks gestation, so the first strategy assessed was induction of labor at 41 0/7 weeks versus expectant management of the pregnancy (Figures A and B) until 42 0/7 weeks gestation. Other theoretical models were created comparing elective induction of labor at 39 0/7, 40 0/7, or 41 0/7 weeks of gestation.

Figure A. Schematic of Decision Tree for 41 week model.

Figure

Figure A. Schematic of Decision Tree for 41 week model.

Figure B. Mode of delivery for 39, 40, and 41 week models.

Figure

Figure B. Mode of delivery for 39, 40, and 41 week models.

Existing literature supports that there is an ongoing risk of both intrauterine fetal demise and experiencing a hypertensive complication of pregnancy which increases by week of gestational age beyond 39 weeks of gestation, so women undergoing expectant management could enter spontaneous labor, have an intrauterine fetal demise, or develop preeclampsia requiring induction of labor. As one of the primary clinical concerns with continuing pregnancy beyond term is the development of placental insufficiency leading to neonatal compromise or death, women undergoing expectant management are frequently subjected to antenatal testing consisting of a nonstress test and measurement of amniotic fluid volume in order to assess fetal well being and placental function. Women undergoing antenatal testing could therefore develop indications for induction based on antenatal testing.

We considered that women undergoing spontaneous or induced labor could experience one or more of six possible events: 1) development of fetal macrosomia; 2) epidural placement; 3) mode of delivery, including spontaneous vaginal delivery, operative vaginal delivery, or cesarean delivery with potential for maternal mortality as a consequence; 4) severe perineal laceration, defined as a perineal laceration injuring the rectal sphincter; 5) shoulder dystocia with the possibility of brachial plexus injury or neonatal demise; and 6) meconium stained amniotic fluid with the possibility of meconium aspiration syndrome, potentially leading to neonatal demise. We obtained estimates for the probabilities of these outcomes as well as related costs and utilities# from the published literature and our systematic review, when possible.

We performed baseline analyses examining each of these six outcomes. Additionally, we evaluated the quality-adjusted life years (QALYs) and costs per QALY associated with each of the strategies.* We performed sensitivity analyses varying each of the inputs into the models over potential ranges. These sensitivity analyses included univariate, multi-way, and Monte Carlo simulations.

Decision Analysis Results

The results below provide information only for Key Questions 1 and 2, evidence describing the maternal or fetal and neonatal risks of elective induction versus expectant management.

Induction of labor at 41 weeks versus expectant management from 41–42 weeks: Our theoretical model of elective induction of labor at 41 0/7 weeks as opposed to expectant management leads to lower rates of neonatal demise, preeclampsia, macrosomia, shoulder dystocia, meconium-stained amniotic fluid, meconium aspiration syndrome, severe perineal lacerations, and operative vaginal deliveries (Table B). We found that elective induction of labor at 41 0/7 weeks is superior to expectant management with an increase in both maternal and neonatal QALYs; 96 percent of the QALYs benefit was due to reduced IUFD.

Table BClinical outcomes per 10,000 women for induction of labor at 41 weeks versus expectant management

Induction of labor at 41 weeksExpectant management at 41 weeks
Cesarean delivery27002700
Perinatal demise<111
Macrosomia12001405
Shoulder dystocia131323
Meconium stained fluid22402436
Meconium aspiration syndrome80170
Severe perineal lacerations561644
Operative vaginal deliveries13301482
Preeclampsia0120

Elective induction of labor at 41 0/7 weeks is more expensive as compared to expectant management. The average cost per woman of an induction at 41 0/7 weeks is $10,139 as compared to $9770 for expectant management for an average incremental cost of $368 per induction. In terms of cost-effectiveness, we find that it would cost an additional $10,789 per additional QALY. Typically, interventions are considered cost-effective if they are less than $50,000 to $100,000 per QALY. Thus, induction of labor at 41 0/7 weeks is a cost-effective intervention by conventional thresholds for cost effectiveness.

Our results remained robust during sensitivity analysis. We did not find substantial changes in outcomes or cost-effectiveness in univariate sensitivity analyses. Even with adjustment of the cesarean delivery rate from the baseline where the cesarean delivery rates were equal, through no difference, to a 22 percent increase in cesarean delivery, the overall QALYs remained higher in the elective induction group and this strategy remained cost-effective.

Induction of labor at 40 weeks versus expectant management from 40–41 weeks. Our theoretical model of elective induction of labor at 40 0/7 weeks as compared to expectant management leads to a lower rate of all adverse obstetric outcomes, including cesarean delivery, neonatal demise, pre-eclampsia, macrosomia, shoulder dystocia, meconium-stained amniotic fluid, meconium aspiration syndrome, severe perineal lacerations and operative vaginal deliveries (Table C). Further, elective induction of labor at 40 0/7 weeks is superior to expectant management until 41 0/7 weeks, with an average of 56.916 total QALYs for an induction of labor at 40 0/7 weeks versus an average of 56.889 total QALYS for expectant management: An incremental gain of 0.027 QALYs.

Table CClinical outcomes per 10,000 women for induction of labor at 40 weeks versus expectant management until 41 weeks

Induction of labor at 40 weeksExpectant management until 41 weeks
Cesarean delivery24202420
Neonatal demise<19
Macrosomia8001105
Shoulder dystocia109330
Meconium-Stained Fluid17001985
Meconium-Aspiration Syndrome4363
Severe perineal lacerations426514
Operative vaginal deliveries10901270
Pre-eclampsia0120

Elective induction of labor at 40 0/7 weeks is more expensive as compared to expectant management. The average cost per woman of an induction at 40 0/7 weeks is $10,030 compared to $9760 for expectant management, for an average incremental cost of $269 per induction. In terms of cost-effectiveness, it would cost an additional $9932 per added QALY. Thus, induction of labor at 40 0/7 weeks is a cost-effective intervention in the baseline analysis.

Our results remained robust during univariate sensitivity analysis. However, incorporating uncertainty in multiple input variables through Monte Carlo simulation, elective induction of labor was cost-effective in approximately 55 percent of the cases.

Induction of labor at 39 weeks versus expectant management from 39–40 weeks and expectant management from 39–41 weeks. Our theoretical model of elective induction of labor at 39 0/7 weeks compared to expectant management until either 40 0/7 or 41 0/7 weeks leads to a lower rate of all adverse obstetric outcomes, including neonatal demise, pre-eclampsia, macrosomia, shoulder dystocia, meconium-stained amniotic fluid, meconium aspiration syndrome, severe perineal lacerations, and operative vaginal deliveries. Table D shows the clinical outcomes associated with each strategy for a cohort of 10,000 women.

Table DClinical outcomes per 10,000 women for induction of labor at 39 weeks versus expectant management until 40 or 41 weeks

Induction of labor at 39 weeksExpectant management until 40 weeksExpectant management until 41 weeks
Cesarean delivery223022272349
Perinatal demise<1512
Macrosomia500763997
Shoulder dystocia87107346
Meconium-Stained Fluid109816991921
Meconium-Aspiration Syndrome274559
Severe perineal lacerations380430506
Operative vaginal deliveries96610891270
Pre-eclampsia090210

Elective induction of labor at 39 0/7 weeks is more expensive compared to expectant management until either 40 0/7 or 41 0/7 weeks. The average cost per woman of an induction at 39 0/7 weeks is $9,568 versus $9253 for expectant management until 40 0/7 weeks and $8915 for expectant management until 41 weeks. Thus, the incremental cost per woman induced is $316 compared to expectant management to 40 0/7 weeks and $338 per woman expectantly managed to 40 0/7 weeks compared to expectant management until 41 0/7 weeks. In terms of cost-effectiveness, it costs an additional $20,222 per additional QALY compared to expectant management until 40 0/7 weeks and an additional $13,900 per additional QALY as compared to expectant management until 41 0/7 weeks. Thus, in our base-case analysis, elective induction of labor at 39 0/7 weeks reaches conventional thresholds for cost effectiveness. However, in sensitivity analysis, the cost-effectiveness of elective induction of labor was not particularly robust. When considering the effect on cesarean delivery, induction of labor is the dominant strategy if the rate of cesarean delivery is less than 75 percent of the cesarean rate with expectant management. Elective induction is cost-effective at $50,000 until the risk of cesarean delivery is 14 percent higher with an induction of labor. Elective induction is cost-effective at $100,000 until the risk of cesarean delivery is 22 percent higher with induction, and at an increased risk of 35 percent or higher, induction of labor is dominated (more expensive and less effective) as compared to expectant management until 40 wks.

In the probabilistic sensitivity analysis using a Monte Carlo simulation, in 29.5 percent of the trials induction of labor at 39 weeks was the dominant strategy (less expensive and more effective). In 25.7 percent of trials it was more effective but more costly, and in 44.8 percent of the trials it was dominated (less effective and more costly). Using a willingness-to-pay threshold of $100,000, induction of labor at 39 weeks is cost-effective in 52.5 percent of the trials. At a willingness to pay of $50,000, it is cost-effective in 49.5 percent of trials.

In summary, our cost-effectiveness analysis suggests that elective induction of labor at 41 weeks improves maternal and fetal outcomes and is cost effective. Our analyses also suggest that elective induction of labor prior to 41 weeks may improve outcomes and could reach conventional thresholds for cost effectiveness. However, there is additional uncertainty about outcomes for elective induction prior to 41 weeks because less evidence is available. All of our model-based analyses should be considered exploratory and hypothesis generating, rather than definitive, because the strength of evidence for model inputs is generally low.

Discussion

The key finding of this review is that women undergoing elective induction of labor have the same or lower rates of cesarean delivery compared with women who are managed expectantly. This result is consistent with other meta-analyses of randomized trials of induction of labor at term and postterm. It is, however, contrary to the commonly held dogma that induction of labor increases the risk of cesarean delivery. This belief is supported by the literature, which compares induction of labor to spontaneous labor, generally finding a higher rate of cesarean delivery among women who are induced. However, given that the actual choice faced by clinicians and their patients is either induction of labor or expectant management of the pregnancy, the comparison of induction of labor to spontaneous labor as a methodologic approach to elective induction of labor does not produce results that are clinically relevant or that can be utilized to counsel women prospectively.

There is a moderate amount of evidence from the current report and prior meta-analyses that elective induction of labor at 41 0/7 weeks of gestation leads to a lower rate of cesarean delivery and meconium-stained amniotic fluid. However, there is a paucity of evidence evaluating the cesarean delivery rate among women electively induced prior to 41 0/7 weeks of gestation. Furthermore, prior to 39 0/7 weeks of gestation, concern for potentially increasing neonatal morbidity with higher rates of respiratory distress syndrome is warranted, particularly in women with poor pregnancy dating.

It does appear that elective induction of labor at 41 0/7 weeks of gestation is supported by a moderate amount of evidence, although many maternal and neonatal outcomes have not been well studied. At gestational ages prior to 41 0/7 weeks, the evidence is insufficient. Moreover, translation of these findings to the population at large in various practice settings has not been well studied. How elective induction of labor may be utilized in non-study settings requires careful consideration by policymakers, clinicians, and patients alike to avoid an expensive intervention that actually may increase cesarean delivery and associated morbidity in current and future pregnancies.

Despite the findings of the current review, it is unclear how the results of such studies translate into clinical practice. As with many interventions, the practice in academic centers under study conditions may not represent the practice in the majority of community hospitals. In particular, there are concerns regarding the implications of such studies related to mode of delivery. Whether a cesarean delivery is the end result of a trial of labor is affected by numerous demographic and medical factors, but, ultimately it is the decision of the provider caring for the laboring woman. The time and financial pressures on clinicians may potentially affect how elective induction of labor affects the risk of cesarean delivery, and, in turn, other maternal and neonatal outcomes in current and future pregnancies. For example, in a practice setting which incorporates the use of laborists, practitioners dedicated to care in the labor and delivery unit (similar to hospitalists in internal medicine), being patient during an induction of labor has far less economic or time pressure on the practitioner. Alternatively, for clinicians who are charged with both in house obstetric care and simultaneously are providing care in the outpatient setting, there are both economic and time pressures to minimize the length of labor whether through augmentation or, in some cases, cesarean delivery.

Limitations of the systematic review. The existing evidence is limited in number of studies, number of well-designed studies, number of adequately powered studies, the breadth of reported outcomes, and analytic design. In terms of the identified literature, there was a wide distribution in terms of both geography and time. It is particularly concerning that one of the principal outcomes of interest was cesarean delivery, as cesarean delivery rates are extremely culturally and time dependent over the last three decades. Thus, a study conducted in one decade may not necessarily inform practice in another decade with respect to cesarean delivery. In addition to the quality of evidence, the overall quantity of studies was also quite poor. For the vast majority of outcomes, there were no more than five studies. Synthesis of the literature with such few studies is challenging as a single study may affect the outcomes and introduce heterogeneity.

One of the most important limitations was the problem of study design. While most RCTs were properly designed to compare elective induction of labor to expectant management of pregnancy, several of the studies we identified used an analytic design which excluded women who were allocated to the expectant management arm and were ultimately induced, which makes interpretation difficult. While the studies examining induction of labor at 41 0/7 weeks of gestation as compared to expectant management were generally specific with respect to gestational age, the studies before 41 0/7 weeks of gestation did not have specific randomization arms at 39 0/7 and 40 0/7 weeks of gestation, so it is impossible to determine what particular strategy at 39 or 40 weeks of gestation will lead to the best overall outcomes utilizing the existing literature.

Limitations of decision analysis. There are a number of important limitations of using decision analysis and cost-effectiveness analysis to address this issue. First, we used models to represent clinical scenarios; these models are necessarily limited in scope and do not capture all relevant considerations for this decision. While a more complex model may get closer to representing the true clinical picture, such complexity increases the demand for evidence about inputs and may make the model difficult to interpret. Finally, for the analyses, there are limitations in the existing probability, cost, and utility data. While we conducted sensitivity analyses over wide ranges of these inputs, better probabilities, costs, and utilities would certainly facilitate more accurate estimates of the outcomes and cost-effectiveness of elective induction of labor. To address the uncertainty in model inputs, a wide range of sensitivity analyses were run to examine the outcomes and cost-effectiveness. Consistent with the clinical studies, the robustness of these analyses varied by gestational age. At 41 0/7 weeks of gestation, in these sensitivity analyses, it appears that our findings were generally robust to the potential benefits and cost-effectiveness of elective induction of labor. However, the results were less robust at 40 0/7 and 39 0/7 weeks of gestation indicating that further research to better characterize the potential outcomes of elective induction of labor at these gestational ages needs to be conducted before recommendation of policies at either of these gestational ages can be supported. We consider our analyses exploratory, and they confirm the potential value of clinical trials that address the outcomes associated with elective induction of labor.

Future research. There is a need for appropriately designed and powered studies to examine the effect of elective induction of labor as compared to expectant management of pregnancies, particularly prior to 41 weeks of gestation. The optimal study designs would be prospective, randomized, controlled trials. Such studies need to be stratified by parity and cervical status and examine a wide range of maternal and neonatal outcomes as well as costs. In addition, other important population characteristics to consider is variation by maternal age, race/ethnicity, and varying moderate risk conditions such as non-insulin dependent gestational diabetes. In order to be appropriately powered, consideration of the estimated samples sizes would indicate that a sample size between 2,000 and 15,000 would be necessary depending on whether the intent was to power for some rare neonatal outcomes (Table E). Since the practice of elective induction of labor is already being utilized at an increasing rate, such a study in the U.S. is long overdue.

Table ESample Size Estimates for Prospective Trial of Elective Induction of Labor as Compared to Expectant Management of Pregnancy

Outcome Studied (baseline risk)Total Sample Size for 80% PowerTotal Sample Size for 90% Power
Cesarean delivery, nulliparas (20%)400532
Cesarean delivery, nulliparas (15%)556742
Meconium (10%)8701,162
Cesarean delivery, multiparas (5%)1,8122,422
Neonatal acidemia (1%)9,34612,506

Cohort studies, either prospective or retrospective, are of some potential value. The validity of these studies depends upon proper study design, comparing women who were electively induced to those who were expectantly managed. In order to capture information on elective induction of labor, such a descriptor should be added to birth certificate data. In addition to study design, data analysis also requires careful attention to potential confounding in such studies. Confounders such as parity, cervical status, gestational age, and complications of pregnancy need to be considered closely and controlled for with multivariable statistical techniques. Such cohort studies can also examine the predictors of a successful induction.

When addressing issues involving elective induction of labor, one must consider the intended goal. Similar to the commentary in the AHRQ report on cesarean delivery by maternal request, (CDMR) which noted that since women may go into labor and deliver via one of three modes of delivery (a spontaneous vaginal delivery, operative vaginal delivery, or cesarean delivery), one must consider planned or intended modes of delivery. In the setting of elective induction of labor, the comparison group, which consisted of women whose pregnancy were expectantly managed, can experience either spontaneous labor, or subsequent development of complications of pregnancy that requires induction of labor. Further, these potential outcomes, i.e., spontaneous labor, complications of pregnancy, or induction of labor, can occur at any point in the future at a wide variety of gestational ages. It was surprising that even when the study design of prospective RCTs were appropriate, several authors analyzed the data by comparing induction of labor to spontaneous labor rather than induction of labor to expectant management as intention to treat. In both RCTs and observational studies, strict use of the appropriate control group, women being managed expectantly, is important.

Outcomes measured. In studies of elective induction of labor compared to expectant management, the focus should be on consistently reporting a wide variety of perinatal outcomes. While we anticipated examining a wide range of outcomes, in reality we obtained information only on a few and were able to synthesize information only on a handful. With respect to mode of delivery, the outcomes, cesarean and operative vaginal delivery, were usually recorded. However, to further determine the effect of labor induction on specific modes of delivery, it would be beneficial to report the indications for both cesarean delivery and operative vaginal delivery. In particular, if a “failed induction” is the indication for cesarean delivery, it would be helpful to report the number of hours involved in the attempted labor induction, and the methods (e.g. prostaglandins, Foley bulb, oxytocin, AROM) utilized, as well as the timing of these methods relative to different phases/stages of labor. Further, since there is some evidence regarding induction and augmentation of labor and fetal position,79, 80 which, in turn, is associated with mode of delivery, fetal position should be recorded as an outcome.

Other maternal outcomes which should be routinely reported in studies of elective induction of labor include the following: Estimated blood loss, incidences of postpartum hemorrhage, blood transfusion, chorioamnionitis, endomyometritis, perineal lacerations, epidural use, length of hospital stay, as well as uncommon but severe morbidities such as pulmonary embolus, amniotic fluid embolus, hysterectomy, and mortality. Since these outcomes are both more severe and less frequent, it is difficult to garner sufficient power to evaluate in a single prospective RCT; thus larger health system or birth certificate data could include elective induction of labor, and large cohort studies could potentially accurately quantify these complications. Long term outcomes such as subsequent fertility, subsequent placentation, subsequent mode of delivery, and pelvic floor injury as represented by urinary incontinence, fecal incontinence, and pelvic organ prolapse should also be examined.

Neonatal outcomes that should be reported routinely in studies intending to examine the effects of labor induction include the following: Umbilical artery blood gases, 5-minute Apgar score, particularly 5-minute Apgar less than 4, respiratory distress syndrome, transient tachypnea of the newborn, presence of meconium-stained fluid, meconium aspiration syndrome, neonatal sepsis, admission to intensive care nursery (ICN), shoulder dystocia, birth trauma including brachial plexus injury, facial nerve palsy, skull fracture, other fractures, cephalohematoma, subgaleal hemorrhage, intracranial hemorrhage, hyperbilirubinemia, birthweight, IUGR, macrosomia, hypoglycemia, polycythemia, length of stay, breastfeeding, and mortality (antepartum, intrapartum, and neonatal). Long-term outcomes such as infant and childhood outcomes of behavior and intelligence should also be assessed. Similar to maternal outcomes, due to the low incidence rate of these outcomes, even large prospective trials are not adequately powered to assess these outcomes. If properly designed and well executed, large cohort studies may potentially overcome limited power and some of the inherent flaws of observational studies, potentially offering vital information to elucidate the rate of these outcomes in association with induction of labor.

In addition to the more traditional clinical outcomes, economic and quality-of-life measures such as patient preferences or utilities should also be considered in future studies of elective induction of labor. Qualitative studies of how women perceived their birth experience in the setting of elective and indicated induction of labor, how they felt their preferences were incorporated into the decision-making process, whether they felt pressured by providers to choose one clinical path or another, how they were counseled and consented, and how their birth experience affected their perceptions of quality of life in future pregnancies all need to be conducted. Specific quantitative measures of patient quality of life would also contribute to the discussion. Both measures of pain and utility on labor and delivery as well as quality of life measures throughout the short- and long-term postpartum periods would inform the understanding of how individuals perceive this intervention. Interestingly, while elective induction of labor allows for some control as to when labor will begin, it also may take the management of early labor out of the parturient's control. How women perceive this intervention will greatly inform the discussion regarding whether it should be routinely offered, and how it might be best conducted to optimize perinatal outcomes and maintain patient satisfaction. Specific economic measures such as micro-costing all of the labor, supplies, time costs, and overhead costs of the induction of labor experience should be examined. When determining how to use societal dollars to facilitate better health outcomes, allocation of these scarce resources cannot occur without reproducible estimates of these costs. In addition, these economic and quality of life issues should be estimated in subsequent pregnancies as these are affected by prior experiences and outcomes on labor and delivery.

Conclusions

In this systematic review and decision analysis of elective induction of labor, we found that overall elective induction of labor as compared to expectant management of the pregnancy was associated with an approximately 20 percent reduction in the rate of cesarean delivery and a 50 percent reduction in the presence of meconium in the amniotic fluid. However, the majority of these studies were in women at or beyond 41 0/7 weeks of gestation; prior to 41 weeks of gestation, there was insufficient evidence from the review to address these outcomes. These findings are consistent with other meta-analyses of induction of labor in postterm and term pregnancies, but are contrary to many observational studies. The existing literature is not powered to examine many of the other complications of pregnancy; however it is assumed that a number of complications must be reduced by elective induction of labor, simply because pregnancy complications such as preeclampsia or IUFD can no longer occur if the pregnancy is interrupted by induction of labor. These findings were reflected in the results of our exploratory decision-analytic models. Further, when we incorporated costs into the models, it appears that elective induction of labor is a cost-effective intervention at 41 weeks of gestation and may potentially be so at earlier gestations. The results prior to 41 weeks of gestation require further examination in a large, prospective randomized trial before routine adoption into clinical practice. Further, because of the heterogeneity in the management of labor induction, which varies widely between providers and institutions, careful examination of the impact of such policies in a wide variety of settings should be explored before elective induction of labor is routinely adopted as a potential policy to prevent complications of term pregnancies.

Utilities are a measure of quality of life, usually expressed on a 0 to 1 scale, which assess how a patient values a health state state.

QALYs are the product of life expectancy multiplied by the quality of life of the health states that a person experiences is a measure that combines both of these effects.

Footnotes

#

Utilities are a measure of quality of life, usually expressed on a 0 to 1 scale, which assess how a patient values a health state state.

*

QALYs are the product of life expectancy multiplied by the quality of life of the health states that a person experiences is a measure that combines both of these effects.

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