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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.)

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

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Maternal and Neonatal Outcomes of Elective Induction of Labor.

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1Introduction

There are a number of complications of pregnancy that confer significant ongoing risk to the mother or fetus (e.g., preeclampsia; preterm premature rupture of the membranes (PPROM); intrauterine growth restriction (IUGR); and postterm pregnancy (pregnancies that progress to and beyond 42 0/7 weeks, or 294 days, gestational age)). For these conditions, induction of labor is often the principal medical intervention utilized to decrease both maternal and neonatal morbidity and mortality. As the proportion of women with complications of pregnancy has increased in the U.S., the rate of medically indicated induction of labor has concomitantly risen from 9.5 percent in 1990 to 22.1 percent in 2004.81, 82 Over the last decade, pregnant women are older, more likely to be overweight or obese, and have higher rates of chronic illnesses such as diabetes and chronic hypertension.82 In turn, these women have higher risks of preeclampsia and IUGR necessitating induction of labor.

In addition to the rise in the rate of indicated induction of labor, it seems that there has also been an increase in the rate of induction of labor that is not indicated for a medical reason.8385 For example, Zhang et al. report that while the overall rate of labor induction increased from 9.5 percent in 1990 to 19.4 percent in 1998, the increase for clinically indicated induction was less.84 This suggests that nonindicated induction of labor has risen even more rapidly than the overall rate.

When a medical indication for induction of labor cannot be identified, it is termed an elective induction of labor. Motivated by both patients and clinicians, elective induction of labor has been utilized for decades. Pregnant women may wish to end their pregnancy because of physical discomfort, concerns that their labor may progress too quickly to ensure timely arrival at the hospital (and perhaps have an epidural) before delivering, convenience of scheduling, or ongoing concerns that they or their baby may be at risk for complications.81 Clinicians (e.g., obstetricians, family-practice physicians, midwives) may have both non-medical and medical reasons for recommending elective induction of labor for their patients.82 For example, they too may wish to end their patients' physical discomfort or have concerns about their patients' distance from the hospital. Clinicians may also be concerned about the risk of developing either complications of pregnancy (e.g., preeclampsia) or intrauterine fetal demise.86, 87 Clinicians may also observe clinical signs or symptoms that may not quite meet strict criteria for a particular diagnosis and thus not have a medical indication for induction of labor. However, when individualized to that particular clinical scenario, it may be felt that induction of labor may provide a greater benefit over expectant management of the pregnancy. A specific example clinicians may use to recommend an induction could be an elevation in blood pressure higher than the patient's baseline yet not diagnostic for gestational hypertension in a non-compliant patient at 40 0/7 weeks of gestation. Established guidelines generally recommend that in the absence of other signs and symptoms, or laboratory results indicative of preeclampsia, continued expectant management should be utilized in such patients.88 However, a clinician may reasonably decide that in such a patient at risk of developing gestational hypertension or preeclampsia who may not return for timely prenatal care, the benefits of labor induction may potentially outweigh the risks of expectant management. Using strict diagnostic criteria, such scenarios are classified as elective induction of labor. Whether these types of inductions are beneficial for the patients is unclear.

Clinicians may also have real or perceived economic incentives to recommend elective induction of labor. Induction of labor, on average, generates greater reimbursements for the clinician only if it leads to higher cesarean delivery rates, and even then the marginal increase in reimbursement is generally quite small. As it is a widely held belief that induction of labor is associated with higher rates of cesarean delivery, providers may believe that they have an economic incentive to encourage induction of labor. However, as we discuss below, cesarean delivery rates may actually be lower in women who have elective induction of labor than those who have expectant management. Thus, clinicians' economic incentives may not to be exclusively related to direct reimbursement. Many pregnant women prefer to have their doctor or midwife present at their delivery: When choosing a practice for prenatal care, a common question is, “Who will deliver my baby?” For many women, the answer of “Whomever is on call” is simply not satisfactory. These women may seek providers who will endeavor to be available for their delivery. Nine months later, clinicians who have agreed to be available for their patients' deliveries have an incentive to induce labor during times when they are on call. In addition, offering such a practice as elective induction of labor may lead to attracting more patients, in general, to the practice leading to higher volume and greater reimbursements. Such supply-side incentives may lead to increases in elective induction of labor without specific changes in reimbursement, because of marginal time costs to the providers.

From a societal perspective, if elective induction of labor led to similar medical outcomes and costs as expectant management, such a practice could seem reasonable and acceptable. Whether medical outcomes are similar, however, is uncertain. The prevailing wisdom regarding elective induction of labor is that induction increases the risk of cesarean delivery.89 However, in prospective, randomized, controlled trials, several studies have compared the rates of cesarean delivery between women with induction of labor and expectant management, and generally concluded that the cesarean rate was unchanged or lower among the induced group.27, 74 A meta-analysis of postterm pregnancy that included women at both 41 0/7 and 42 0/7 weeks gestation found a reduction in the cesarean delivery rate among women who were induced (OR 0.88; 95 percent CI 0.78–0.99) compared to women who underwent expectant management.90 Similarly, a recent Cochrane review which stratified groups by gestational age demonstrated a non-significant decrease in the rate of cesarean delivery for women who underwent induction of labor (OR 0.92; 95 percent CI 0.76–1.12).91 Interestingly, a stratified analysis of the three studies of women at less than 41 0/7 weeks gestation showed a reduction in the rate of cesarean delivery in the elective induction group (OR 0.58; 95 percent CI 0.34–0.99).

The comparative costs of elective induction of labor and expectant management are also not well understood. Induction of labor has been associated with an increase of $1,237 per patient over expectant management.92 If elective induction of labor increases the rate of cesarean delivery, such a practice would be very costly. Alternatively, if, as suggested by prior systematic reviews, elective induction of labor decreases the rate of cesarean delivery, it may instead be cost saving.1

Clearly, the effect of elective induction of labor on the frequency of cesarean delivery is a critical uncertainty that requires detailed analysis to help clinicians and policymakers determine the role for elective induction of labor in current obstetric practice. However, the majority of the available literature on the association between elective induction of labor and the cesarean delivery rate is subject to serious methodologic flaws that merit discussion. Similarly, while costs assessed at the individual level may appear to be higher in the short-term among those patients with elective induction of labor, considerations of both societal and long-term perspectives is warranted. In the next section, we discuss the key methodologic issues related to gestational age and pregnancy dating and how they can influence the estimates of the effects of labor induction on perinatal outcomes and costs to society.

Gestational Age and Elective Induction of Labor

Before going any further, it should be clarified that throughout this report, 41 0/7 week and 41 weeks of gestation will be utilized interchangeably. The same is true for 39 0/7 and 39, 40 0/7 and 40, and 42 0/7 and 42. We endeavor not to use the phrase ‘the 42nd week of pregnancy’ which can refer to either time period 41 0/7 until 41 6/7 or 41 1/7 until 42 0/7. When we are referring to a particular time period, we will delineate the time period by the starting and ending week of gestation around the time period such as 41 to 41 6/7 weeks of gestation.

Additionally, there are specific terms that are utilized to describe gestational age and the fetus or infant that we have attempted to use consistently throughout this report. A postterm pregnancy is one that is 42 0/7 weeks or beyond. The terms post-dates and prolonged pregnancy are poorly and inconsistently defined thus, we endeavor not to use these terms. We have attempted to use fetal to refer to pre-delivery outcomes, neonatal for outcomes that occur in the first 28 days of life, perinatal to capture the combined fetal and neonatal periods, and infant for outcomes beyond 28 days and prior to one year of life.

As mentioned above, there are many published studies which find a positive association between induction of labor and cesarean delivery.11, 20, 89 The majority of these studies employed either a retrospective cohort or case-control study design. Since many women who have an induction of labor do so for either late-term (41 0/7 to 41 6/7 weeks of gestation) or postterm (42 weeks of gestation and beyond) pregnancies, one problem with these studies is there is often a difference in gestational age between the women who undergo induction of labor and those in the control group, who are typically women experiencing spontaneous labor, with more women in the induction group being postterm.97 Further, the risk of cesarean delivery varies by week of gestational age in both term and postterm pregnancies, increasing with increasing gestational age.98, 99 Thus, if women who are induced are compared to women experiencing spontaneous labor, gestational age is a confounding variable because it is associated with both the predictor (in this case, induction of labor) and the outcome of interest (cesarean delivery). While older studies did not generally use multivariable regression techniques to control for confounding bias,66, 74 more recent studies have done so.47, 48 Although this adjustment can decrease the bias in the effect estimates of labor induction on cesarean delivery, it does not entirely eliminate it. In contrast to these observational studies, there are a number of randomized controlled trials of induction of labor which found either a decrease or no difference in cesarean delivery rates. Studies of pregnancies at or beyond 41 weeks of gestation have demonstrated a decrease in cesarean delivery among women who have undergone induction of labor.27, 90 In women with diabetes100 and presumed macrosomia101 who have been induced, prospective trials report no statistically significant difference in rates of cesarean delivery.

How is such a difference in results between cohort and case-control studies and prospective randomized, controlled trials explained? In addition to bias due to residual confounding, another important reason is a fundamentally flawed study design present in most non-randomized studies: By either matching on gestational age or utilizing multivariable techniques, the investigators often make a direct comparison between women who have induction of labor at a given gestational age versus women who experience spontaneous labor at that same gestational age (Figure 1.1.A). Unfortunately, when caring for a pregnant woman at term, clinicians are not actually choosing between induction of labor and spontaneous labor; rather, the options clinicians and their patients face are either elective induction of labor now or continuing expectant management of the pregnancy. Expectant management of the pregnancy simply involves nonintervention at any particular point in time and allowing the pregnancy to progress to a future gestational age. Thus, it can result in either spontaneous labor or medically-indicated induction of labor at a greater gestational age (Figure 1.1.B). Furthermore, the indications for inductions of labor at a greater gestational age may include pregnancy or medical complications such as preeclampsia, oligohydramnios, intrauterine growth restriction, nonreassuring antenatal testing, or postterm pregnancy, all of which have also been associated with an increased risk of cesarean delivery.102104 One recent study underscored this methodologic concern by finding that when compared to spontaneous labor, induction of labor was associated with an increased risk of cesarean delivery, but when compared to expectant management of the pregnancy, it was associated with a decreased risk of cesarean delivery.

Figure 1.1.A. Comparison of induction of labor to controls by week of gestation.

Figure 1.1.A

Comparison of induction of labor to controls by week of gestation. In many observational studies, induction of labor is compared to controls by week of gestation which appears to (but does not actually) capture the confounding effect of gestational age. (more...)

Figure 1.1.B. Comparison of induction of labor to expectant management.

Figure 1.1.B

Comparison of induction of labor to expectant management. In a prospective, randomized, controlled trial, induction of labor is actually compared to expectant management. Clinicians are deciding between induction of labor at the current gestational age (more...)

Thus, when considering the clinical question of the effect of labor induction on the risk of cesarean delivery, gestational age cannot simply be controlled for using straightforward statistical techniques as is appropriate for other classic confounders. Rather, a study design comparing women undergoing induction of labor at a specific gestational age to women who deliver as a result of either spontaneous labor or induced labor at a greater gestational age is the only way non-randomized data should be utilized to examine the effect of induction of labor on mode of delivery. Similarly, if one wishes to examine the effect of induction of labor on other outcomes, this issue of gestational age needs to be examined. For example, if one was to examine the effect of induction of labor on preeclampsia by comparing rates of preeclampsia in induced women to those in spontaneous labor, since preeclampsia is an indication for induction of labor, it is assumed that an increased risk in the induction of labor group would be found. Of course, this is nonsensical since it is actually a reversal of the causality relationship. However, if one examined this effect in either a prospective randomized trial or utilizing the comparison between women induced at one gestational age (not for preeclampsia) compared to those women managed expectantly beyond that particular gestational age, we would find that induction of labor prevents preeclampsia since one cannot develop preeclampsia next week if they are being induced today. Similarly, this protective effect exists for other complications such as intrauterine fetal demise and macrosomia. However, to date, there are no observational studies of these specific outcomes framed in such a fashion. Thus, we must rely exclusively on randomized trial evidence to evaluate most perinatal outcomes when comparing induction of labor to expectant management of pregnancy.

Given the rising incidence of elective induction of labor, the non-medical incentives driving its use, and the lack of consensus regarding its effect on key maternal and fetal outcomes, we sought to systematically evaluate the evidence regarding the use of elective induction of labor and explore gaps in the literature with simulation modeling. A better understanding of all aspects of elective induction of labor is important. Ideally, research on induction of labor should include insight into the incentives facing both the pregnant women and clinicians such as the outcomes and costs related to induction of labor and the sociocultural factors which may affect the associated outcomes, particularly mode of delivery.

Key Questions and Analytic Framework

Given this background and the methodological concerns, we sought to conduct an analysis of the existing literature in order to answer the following Key Questions on the effects of elective induction of labor:

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?

To address these Key Questions, we performed a systematic review of the literature. For Key Questions 1 and 2, we included studies that included women with both expectant management as well as spontaneous labor as the control group since the latter is the most common comparison group for elective induction of labor. For Key Questions 3 and 4, we expanded our inclusion to studies examining predictors of failure and the definition of failure in non-elective induction of labor. To address the gaps in the published literature, we conducted cost-effectiveness analyses to evaluate the effects of key predictors, such as mode of delivery, on overall outcomes and costs of elective induction of labor.

Organization of This Report

The remainder of this report is organized into the following sections: Chapter 2 - Systematic Review of Elective Induction of Labor describes the methods used to conduct the systematic review as well as the results for Key Questions 1 through 4. Chapter 3 - Decision Analytic Model describes the methods and results of the cost-effectiveness analysis. Chapter 4 - Discussion provides a commentary on the key findings from both the systematic review and the decision analysis, describes the limitations of these findings, and offers recommendations for future research on this topic.

Footnotes

1

Further, since the rate of vaginal birth after cesarean (VBAC) has fallen appreciably over the past decade, the vast majority of women who had cesarean delivery in a prior pregnancy will likely undergo repeat cesarean deliveries in subsequent pregnancies. These repeat cesareans are associated with higher risk of abnormal placentation, including placenta previa and accreta93 which, in turn, are associated with higher risks of maternal morbidity and mortality.94, 95 Prior cesareans have also been associated with higher rates of unexplained intrauterine fetal demise.96 Thus, if elective induction of labor leads to higher rates of cesarean delivery, it may lead to increases in perinatal complications and costs in both current and future pregnancies.

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