Evidence Report/Technology Assessment: Number 71

Vaginal Birth After Cesarean (VBAC)

Summary


Under its Evidence-based Practice Program, the Agency for Healthcare Research and Quality (AHRQ) is developing scientific information for other agencies and organizations on which to base clinical guidelines, performance measures, and other quality improvement tools. Contractor institutions review all relevant scientific literature on assigned clinical care topics and produce evidence reports and technology assessments, conduct research on methodologies and the effectiveness of their implementation, and participate in technical assistance activities.

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Purpose of Report and Target Audience / Overview / Reporting the Evidence / Methodology / Findings / Summary of Evidence / Future Research / Availability of Full Report


Purpose of Report and Target Audience

This report provides a framework for comparing the harms and benefits of delivery options for women with prior cesarean delivery (CD). The information is designed to help consumers, providers, payers, and policymakers in decisionmaking about repeat cesarean or trial of labor (TOL).

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Overview

In 2000, 22.9 percent of all births in the United States occurred by CD. This rate is the highest total CD rate reported since data collection began in 1989. The vaginal birth after cesarean (VBAC) rate, defined as the proportion of women with a prior CD who delivered vaginally, steadily increased from 1989 to 1996. As allowing TOL became more common, practice variation became a larger concern, e.g., expanding criteria for eligibility and medical induction, and for augmentation of labor. In parallel with this liberalization of criteria and management, highly publicized articles suggested that maternal and fetal risks were perceived to be increasing. Subsequently, the VBAC rate has decreased 27 percent from 1996 to 2000. Currently, a crisis in malpractice rates is decreasing the availability of maternity care providers and raising concerns that patients may have limited options, less access to care, and perhaps be at increased risk for complications.

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Reporting the Evidence

The strength and suitability of the evidence regarding the risks of major maternal and infant morbidity and mortality associated with TOL or elective repeat cesarean delivery (ERCD) in women with prior low transverse or unknown scar. The scope of the review was to examine events that were specifically related to having had a prior CD. Comparisons purely about vaginal versus cesarean delivery such as incontinence, pelvic support disorders, and respiratory consequences but not specifically about VBAC or repeat cesarean, were not considered, though these topics are important to consider when deciding upon route of delivery. In judging the suitability of evidence, we took the perspective that the first thing a decision-maker would want to know is whether the risk of these complications is higher for a trial of labor, versus an elective cesarean delivery, under optimal conditions of care. That is, the most relevant evidence would compare the outcomes and risks of a properly managed trial of labor to that of a properly conducted elective cesarean delivery. Some components of obstetric care, as well as some aspects of the setting of this care, might increase the risks of TOL or ERCD. For example, it has been hypothesized that the use (or misuse) of drugs for induction and augmentation might increase the risk of uterine rupture in patients who have had a prior cesarean delivery. We examined the strength of evidence that these factors influence these outcomes and adverse effects and to what extent these factors can explain the results of observational studies of VBAC complications.

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Methodology

Key Questions

Two types of key questions were addressed. The first group (Questions 1- 7) compares the outcomes of a TOL and an ERCD:

  1. What is the frequency of vaginal delivery in women who undergo a TOL (spontaneous onset, induced, and augmented) after prior low transverse cesarean or unknown scar?
  2. How accurate are risk assessment tools for identifying patients who will have a vaginal delivery after a TOL?
  3. What are the relative harms associated with a TOL (spontaneous onset, induced, and augmented) and repeat cesarean?
  4. What is the incidence of uterine rupture, and are there methods for preventing major morbidity and mortality due to uterine rupture?
  5. What are the health status and health-related quality of life for VBAC and repeat cesarean patients?
  6. Regarding VBAC and repeat cesarean, what factors influence patient satisfaction/dissatisfaction with their childbirth experience?
  7. How are economic outcomes related to VBAC, repeat CD, and their respective complications?

The second group (Questions 8-10) address factors influencing the decision to have a TOL:

  1. What individual factors influence route of delivery?
  2. What factors influence a patient's decisionmaking regarding VBAC or ERCD?
  3. How do legislation, policy, guidelines, provider characteristics, insurance type, and access to care affect health outcomes for VBAC candidates?

Relevant studies were identified from multiple searches of MEDLINE® (1966 to 2002) and HealthSTAR (1975 to 2002), from the reference lists of systematic reviews and from local and national experts. The online Cochrane systematic reviews and controlled trials registries, DARE, National Centre for Reviews and Dissemination, and EMBASE databases were searched for relevant literature on specific topics as well. For topics related to patient preferences and satisfaction, PsycINFO and CINAHL® databases were searched. Databases were searched twice during the course of the project, with the final search in March 2002. For all VBAC topics combined, 14,449 citations were retrieved, including 4,867 about spontaneous labor and uterine rupture, 2,528 about ERCD, 2,416 about induction of labor, 2,945 citations about predictors, 1,257 about patient satisfaction, preference and health status, and 436 about cost and access.

All searches were limited to English-language articles published since 1980 (the date of the NIH Consensus Conference on VBAC) in developed countries. The report focused on studies that identified a group of patients with prior cesarean. For patient preferences and satisfaction, studies of the general birthing population, were considered if there were no studies that identified patients with prior cesarean. Studies were excluded if they focused on patients with particular conditions such as gestational diabetes, HIV, preeclampsia, and so on. Exclusions were also made for studies that focused primarily on the following: nulliparous women, vertical, lower vertical, "classical" or "classic" cesarean, vaginal breech delivery, preterm delivery, multiple gestation, or low birth weight.

Two investigators reviewed a random set of titles and abstracts for each topic to select articles for full-text review. When an appropriate level of reliability was reached for inclusion and exclusion of studies, the primary investigator reviewed the remaining titles and abstracts on the topic. Investigators read the full-text version of the retrieved papers and reapplied the initial eligibility criteria. Data from 224 studies were abstracted and included in the evidence tables described in the results section of this report.

Data Abstraction

Included study designs were determined by topic area. Study designs of included articles consisted of randomized controlled trials, cohort studies, case-control studies, cross-sectional studies, large case series (more than 10 subjects), and economic or decision models. All data were abstracted by the lead investigator for the topic. If the lead investigator encountered difficulty in finding or interpreting information in the published report, a second investigator reviewed the article and a consensus was reached.

Assessment of Study Quality

To assess the internal validity of individual studies, we applied a set of design-specific criteria developed by the current U.S. Preventive Services Task Force and additional criteria developed by the NHS Centre for Reviews and Dissemination, based at the University of York in England. In general, studies were rated good if they met all criteria, fair if they addressed some but not all criteria, and poor if they had a "fatal flaw." Investigators were asked to use the study quality ratings as previously described to determine for their topic which quality components were most important in assessing internal validity. This process allowed for some individual topic fit for fatal flaws, etc. A second investigator independently rated all included articles, and disagreements were resolved by consensus.

Data Synthesis

Where appropriate, meta-analysis was performed using WinBugs® or StatsDirect® software. To reduce potential bias, only studies of fair or good quality were included in the analyses.

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Findings

Question 1. Likelihood of Vaginal Delivery

Question 2. Predictive Tools

Question 3. Maternal and Infant Outcomes

General

Maternal

Infant

Question 4. Uterine Rupture

Question 5. Health Status

Question 6. Patient Satisfaction

Question 7. Cost and Health Care Resources

Question 8. Individual Factors

Question 9. Patient Preferences

Question 10. Legal, Provider, Hospital, Insurance Characteristics

General

Legal

Provider

Hospital

Insurance

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Summary of Evidence

The following summarizes the type of study design, the quality of the evidence from studies, and the suitability of the study design to answer the particular question for each key question.

Key Question Study Type1 Quality of Evidence Suitability of Study Design2

Question 1

What is the frequency of vaginal delivery in women who undergo a TOL (spontaneous onset, induced, and augmented) after prior low transverse cesarean or unknown scar?

II-2 Fair-Good: Several large prospective and retrospective studies; mostly consistent findings. Greatest

Question 2

How accurate are risk assessment tools for identifying patients who will have a vaginal delivery after a TOL?

     
Predictive tools II-2 Fair-Good: Large fair and good quality cohort studies suggest tools can provide additional information to predict likelihood of vaginal delivery. Greatest
Imaging modalities I Good: Good quality RCT demonstrated that imaging was ineffective to predict vaginal birth. Greatest

Question 3

What are the relative harms associated with a TOL (spontaneous onset, induced and augmented) and repeat cesarean?

 

II-2

Fair-Poor: Several large cohort studies were inconsistent in their definitions for important health outcomes. Moderate
Maternal Death Fair: Studies consistently found no increased risk of maternal death from TOL versus ERCD. Least
Hysterectomy Fair-Poor: Many studies failed to report indication for hysterectomy. Moderate
Transfusion Fair: Two studies with consistent findings of slightly increased risk for transfusion in TOL although not significant in one. Moderate
Infection Poor: Definitions were inconsistent among studies. Moderate
Incontinence/Pelvic Floor No studies. Moderate
Infant Death Poor: Most studies found increased risk of perinatal death for TOL versus ERCD, but the magnitude of the increase varied greatly. Least
Neurologic Impairment Poor: Few studies of poor quality. Least
Respiratory Impairment No studies. Moderate

Question 4

What is the incidence of uterine rupture of a cesarean scar, and are there methods for preventing poor clinical outcomes?

     
Incidence II-2 Fair-Poor: Several large cohort studies which were inconsistent in terminology; many with consistent findings of increased risk of symptomatic uterine rupture in TOL versus ERCD. Moderate
Methods for preventing poor outcomes II-3 Poor: Few studies, variation in case definition. Fetal bradycardia was frequently associated with uterine rupture; however, inclusion of fetal tracing findings in the definition of uterine rupture makes it difficult to assess the true value. Least

Question 5

What are the health status and health related quality of life for VBAC and repeat cesarean patients?

None No studies of women with prior CD. NA

Question 6

Regarding VBAC and repeat cesarean, what factors influence patient satisfaction/dissatisfaction with their childbirth experience?

III Fair: Two cross-sectional studies with varied findings. Least

Question 7

How are economic outcomes related to VBAC, repeat CD, and their respective complications?

Econ Fair-Good: One good economic model suggests VBAC is cost-effective and provides higher quality of life when chance of vaginal delivery is 76 percent or greater. Greatest

Question 8

What individual factors influence route of delivery?

II-2 Fair-Poor: Several retrospective cohort studies conducted; all vary in items considered, each with limited adjustment for confounders. Moderate

Question 9

What factors influence a patient's decisionmaking regarding VBAC or ERCD?

I,II,III Fair: One good RCT and eight fair quality cohort or cross-sectional studies found women who preferred TOL were more likely to be White, valued the process of labor, and valued social motives such as ease of recovery. Moderate

Question 10

How do legislation, policy, guidelines, provider characteristics, insurance type, and access to care affect health outcomes for VBAC candidates?

     
Legislation II-3 Poor: Few studies that examined only the impact on VBAC rates not safety. None examined the impact of the crisis in malpractice rates on access or safety. Moderate
Guidelines I,II Fair-Good: Several studies with consistent findings that provision of guidelines especially with recommendations of opinion leaders increased VBAC rates; no studies on safety. Moderate
Provider Characteristics II Poor: Several studies, none of which adjusted for differences in baseline risk or potential confounders. Moderate
Hospital II Fair: Consistent findings that teaching hospitals had higher VBAC rates; no comparisons for safety. Moderate
Insurance II Fair: Several studies with conflicting findings. Moderate

1 Study design categories—I: randomized, controlled trials; II-1: controlled trials without randomization; II-2: cohort or case-control; II-3: multiple time series; III: opinions, descriptive epidemiology. U.S. Preventive Services Task Force (1996).
2 Suitability of study design categories—Greatest: For comparison studies: Concurrent comparison groups and prospective measurement of exposure and outcome; For rates: population-based or multicenter prospective cohort studies. Moderate: All retrospective designs or multiple pre or post measurements but no concurrent comparison group; Least: Single pre and post measurements and no concurrent comparison group or exposure and outcome measured in a single group at the same point in time. Community Preventive Services Task Force (2000).

Limitations

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Future Research

Future research should focus on conducting methodologically rigorous studies to provide direct evidence regarding the relative benefits and harms of TOL and ERCD. If randomized trials are not done, good-quality studies of TOL versus ERCD must pay attention to the following:

Population. Studies should be conducted in populations of women who are similar in every respect except choice of delivery route (comparability of groups).

Specificity of intervention. Studies should pay close attention to and account for the importance of co-interventions such as use of oxytocin and other medical agents for augmentation or induction of labor.

Precise and standard outcome measures. Variations in reporting of important clinical outcomes were striking. Studies should consider the following factors in developing outcome measures:

Predictive Tools

Additional studies are needed to measure the accuracy and yields of existing predictive tools. Future studies of predictive tools should include measurements of the consequences of false-positive screens and false-negative screens to determine whether there are clinically important harms that result from screening.

Cost

The costs (rather than charges) of labor and delivery and of the surgical processes are poorly understood. Detailed time-in-motion studies would help to estimate these costs.

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Availability of Full Report

The full evidence report from which this summary was taken was prepared for the Agency for Healthcare Research and Quality (AHRQ) by the Oregon Health & Science University Evidence-based Practice Center (EPC), Portland, OR, under Contract No. 290-97-0018. Printed copies may be obtained free of charge from the AHRQ Publications Clearinghouse by calling 1-800-358-9295. Requesters should ask for Evidence Report/Technology Assessment No. 71, Vaginal Birth After Cesarean (VBAC).

The Evidence Report can also be downloaded as a set of PDF files online at www.ahrq.gov/clinic/evrptpdfs.htm#vbac or as a zipped file at www.ahrq.gov/clinic/evrptfiles.htm#vbac.

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AHRQ Publication Number 03-E017
Current as of March 2003


Internet Citation:

Vaginal Birth After Cesarean (VBAC). Summary, Evidence Report/Technology Assessment: Number 71. AHRQ Publication Number 03-E017, March 2003. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/clinic/epcsums/vbacsum.htm


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