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).

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.

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 decisionmaker 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.

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:

Evidence Report/Technology Assessment

Number 71

Vaginal Birth After Cesarean (VBAC)

Summary

Agency for Healthcare Research and Quality

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES • Public Health Service
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:

8. What individual factors influence route of delivery?

9. What factors influence a patient’s decisionmaking

regarding VBAC or ERCD?

10. 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, crosssectional 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.

Findings

Question 1. Likelihood of Vaginal Delivery

• Rates of vaginal delivery when attempting TOL ranged

from 60 to 82 percent. The largest population-based

2
study reported a rate of 60.4 percent. The combined

vaginal delivery rate for all prospective cohort studies,

largely conducted in tertiary care centers and University

settings, was 75.9 percent.

• There are limited data on the effect of medical induction

and augmentation of labor.

• There was a 10-percent reduction in the likelihood of

vaginal delivery when oxytocin was used for ether

induction or augmentation. There was a similar trend in

reduced likelihood of vaginal delivery with

prostaglandins.

Question 2. Predictive Tools

• Two validated scoring systems categorized women into

groups with likelihoods of vaginal delivery ranging from

roughly 45 to 95 percent.

• One tool was able to stratify more of the population (up

to 50 percent of women choosing TOL) into high and

low probability subgroups, with a relatively low falsepositive rate.

• By using a prospective cohort design and the largest

study population, the best scoring system created a 10-

point score based on the presence or absence of five

variables commonly available for most patient

admissions.

• An RCT clearly demonstrated the inability of X-ray

pelvimetry (XRP) to predict route of delivery reliably.

• Imaging studies that combined the measurements of the

pelvis and fetus showed promising results, but were

limited by their lack of control for confounding and

biases.

Question 3. Maternal and Infant

Outcomes

General

• In the absence of RCTs of TOL versus repeat cesarean,

evidence that is most generalizable comes from large

country, State, or regional population-based studies

(referred to as population-based studies) followed by large

multicenter cohort studies, large single-institution or

single-practice cohort studies, then smaller cohort studies,

respectively.

• There is no direct evidence regarding the benefits and

harms of TOL relative to ERCD in women who are

similar in every respect except choice of delivery route. 

• Several fair and good quality studies provide indirect

evidence about relative benefits and harms of each route.

Maternal

• Maternal death rates did not differ between TOL and

ERCD.

• The best evidence suggests that hysterectomy rates do not

differ between TOL and ERCD.

• No studies examined specifically the risks of incontinence

or pelvic support disorders in women with prior cesarean. 

• Rates of infection were increased in ERCD versus TOL

overall. Studies that performed subgroup analyses for

TOL with and without vaginal delivery consistently

found increased rates of infection for women who

attempted TOL but ultimately had a cesarean delivery.

• There is conflicting evidence regarding whether

induction of labor affects infection rates.

Infant

• There is insufficient evidence regarding the effect of

selected route of delivery and Apgar score or respiratory

morbidity.

• No study measured infant death directly attributable to a

mother’s choice of TOL or repeat CD.

• There is uncertainty about the magnitude of risk of

perinatal death due to TOL. Results from two large

studies differ in the magnitude of increased risk from

TOL versus ERCD (90/1,000 TOL versus 50/1,000

ERCD compared with 12.9/1,000 TOL versus 1.1/1,000

ERCD). Neither study provides direct evidence of risk.

Question 4. Uterine Rupture

• The use of terms among studies is inconsistent.

• Definitions among studies for similar terms are

ambiguous.

• There is no difference in asymptomatic uterine rupture

rates in TOL versus ERCD.

• Symptomatic uterine rupture is significantly more

common in TOL versus ERCD, with an increased risk of

2.7/1000.

• Based on the frequency and severity of symptomatic

uterine rupture, the risk of perinatal death due to a

rupture of a uterine scar is 1.5/10,000 and the risk of

maternal hysterectomy is 4.8/10,000. These rates of

serious complications such as perinatal death are probably

more precise than overall risks from studies measuring

death directly.

• The definition of uterine rupture as an outcome is

confounded by a definition that includes the potential

predictor of fetal heart rate (FHR) tracing abnormality.

• Measurement of frequency of occurrence, predictors for

what population is at greatest risk, and predictors for

poor outcomes are not possible, because of the lack of

standard case definition.

Question 5. Health Status

• There were no studies of health status or health-related

quality of life for VBAC or repeat CD patients.

3
Question 6. Patient Satisfaction

• Studies of patient satisfaction largely consisted of the

patient’s own provider obtaining information about

patient satisfaction, introducing the possibility of

measurement bias.

• Only two cross-sectional studies used methods other than

the patient’s own provider to obtain satisfaction

information.

• No study measured satisfaction for the three types of

delivery outcomes that could be experienced by women

with prior CDs (VBAC, TOL followed by CD, or

ERCD).

Question 7. Cost and Health Care

Resources

• For a TOL success probability of 76 percent or greater,

TOL is more cost-effective and provides higher quality of

life.

• Further evaluation is needed of the sensitivity of the

probability cut point of 76 percent to other potential

predictor variables.

Question 8. Individual Factors

• The vast majority of studies looking at individual factors

that influence the route of delivery were of poor quality

due to the lack of control for confounding factors.

• The factors that were significantly associated with an

increased likelihood of vaginal delivery (i.e., successful

TOL) were maternal age less than 40 years, prior vaginal

delivery (particularly vaginal delivery after cesarean), a

nonrecurrent indication for the prior CD, and favorable

cervical factors.

• The factors that were significantly associated with a

decreased likelihood of vaginal delivery (i.e., failed TOL)

were an increasing number of prior CD, gestational age

greater than 40 weeks, birthweight greater than 4000 g,

and augmentation of labor.

Question 9. Patient Preferences

• Patient preferences for birth choice are unclear because of

the heterogeneity of the 11 included studies.

• Several factors appear related to choice for TOL (White

race, prior vaginal delivery, lower levels of anxiety during

the pregnancy).

• Lack of medical information along with cultural

ideologies might account for minority women being less

likely to attempt a TOL when compared with White

women.

• A woman’s choice for delivery was often based on social

motives (e.g., easier recovery, so she can care for baby and

children at home).

• Only four of 11 studies cited safety for mother or baby as

important reasons for delivery choice.

• It remains unclear whether VBAC education increases the

proportion of women who choose TOL.

Question 10. Legal, Provider, Hospital,

Insurance Characteristics

General

• Studies of legislation, policy, guidelines, hospital

characteristics, provider characteristics, insurance type, or

access to care focus exclusively on VBAC rates rather than

safety.

Legal

• No study provides direct evidence for the impact of

malpractice issues on VBAC or ERCD. 

• One study reported that VBAC rates increased when

legislation was enacted that standardized VBAC

guidelines had to be provided to obstetric providers.

• The best evidence suggests that use of opinion leaders

provides a greater likelihood of changing practice

compared with audit and feedback.

Provider

• Studies of provider characteristics failed to control for

important variables such as patient selection bias.

Hospital

• VBAC rates were higher in teaching hospitals compared

to private, community, regional, or non-teaching

hospitals.

• Three studies conflicted over the effect of hospitals

containing a neonatal intensive care unit (NICU).

Insurance

• There was conflicting evidence regarding whether

insurance status predicts VBAC.

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.

4
5

Key Question Study Quality of Evidence Suitability

Type* of Study

Design†

Question 1

What is the frequency of vaginal delivery in women II-2 Fair-Good: Several large prospective and Greatest

who undergo a TOL (spontaneous onset, induced, retrospective studies; mostly consistent findings.

and augmented) after prior low transverse cesarean

or unknown scar?

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 Greatest

studies suggest tools can provide additional 

information to predict likelihood of vaginal 

delivery.

Imaging modalities I Good: Good quality RCT demonstrated that Greatest

imaging was ineffective to predict vaginal birth.

Question 3

What are the relative harms associated with a TOL II-2 Fair-Poor: Several large cohort studies were Moderate

(spontaneous onset, induced and augmented) and inconsistent in their definitions for important 

repeat cesarean? health outcomes.

Maternal Fair: Studies consistently found no increased Least

Death risk of maternal death from TOL versus ERCD.

Hysterectomy Fair-Poor: Many studies failed to report Moderate 

indication for hysterectomy.

Transfusion Fair: Two studies with consistent findings of Moderate

slightly increased risk for transfusion in TOL 

although not significant in one.

Infection Poor: Definitions were inconsistent among Moderate

studies. 

Incontinence/Pelvic Floor No studies. Moderate

Infant Death Poor: Most studies found increased risk of Least

perinatal death for TOL versus ERCD, but the 

magnitude of the increase varied greatly.

Neurologic impairment Poor: Few studies of poor quality. Least

Respiratory impairment No studies. Moderate

Summary of Evidence of Key Questions
6

Key Question Study Quality of Evidence Suitability

Type* of Study

Design†

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 Moderate

were inconsistent in terminology; many with 

consistent findings of increased risk of 

symptomatic uterine rupture in TOL versus 

ERCD.

Methods for preventing poor outcomes II-3 Poor: Few studies, variation in case definition. Least

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.

Question 5

What are the health status and health related None No studies of women with prior CD. NA

quality of life for VBAC and repeat cesarean patients?

Question 6

Regarding VBAC and repeat cesarean, what factors III Fair: Two cross-sectional studies with varied Least

influence patient satisfaction/dissatisfaction with findings.

their childbirth experience?

Question 7

How are economic outcomes related to VBAC, Econ Fair-Good: One good economic model suggests Greatest

repeat CD, and their respective complications? VBAC is cost-effective and provides higher 

quality of life when chance of vaginal delivery is 

76 percent or greater.

Question 8

What individual factors influence route of delivery? II-2 Fair-Poor: Several retrospective cohort studies Moderate

conducted; all vary in items considered, each 

with limited adjustment for confounders.

Question 9

What factors influence a patient’s decisionmaking I, II, III Fair: One good RCT and eight fair quality Moderate

regarding VBAC or ERCD? 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.
7

*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).

†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).

Key Question Study Quality of Evidence Suitability

Type* of Study

Design†

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 Moderate

impact onVBAC rates not safety. None 

examined the impact of the crisis in malpractice 

rates on access or safety.

Guidelines I, II Fair-Good: Several studies with consistent Moderate

findings that provision of guidelines especially 

with recommendations of opinion leaders 

increased VBAC rates; no studies on safety.

Provider II Poor: Several studies, none of which adjusted Moderate

Characteristics for differences in baseline risk or potential 

confounders.

Hospital II Fair: Consistent findings that teaching hospitals Moderate

had higher VBAC rates; no comparisons for 

safety.

Insurance II Fair: Several studies with conflicting findings. Moderate

Limitations

• Data are insufficient to allow conclusions about the most

appropriate delivery choice for a given patient.

• Studies suffered from inconsistent and imprecise

definitions for important outcomes.

• Studies frequently failed to ensure comparability between

TOL and ERCD groups.

• No study or collection of studies, provide data about the

impact of practice variation, provider characteristics, legal

considerations such as the effect of rising malpractice

rates on the safety of TOL or ERCD.

• The degree to which the association between fetal

bradycardia and poor perinatal outcome from uterine

rupture rather than confounding by factors detection bias

is unclear.

• The degree to which the association between TOL and

perinatal death reflects causation rather than confounding

by factors such as misclassification of cases, lethal

conditions of the fetus, or detection bias is unclear.

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 cointerventions 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:

• Etiology. Outcomes such as hysterectomy, infection,

maternal mortality, and perinatal mortality must pay

specific attention to explicitly identifying the etiology.

Lack of precision in this regard allows for both under and

overreporting of cases due to misclassification. Examples

include whether hysterectomy was performed due to

maternal hemorrhage secondary to clinically significant

uterine rupture versus hemorrhage due to abruption,

uterine rupture through the uterine fundus in a woman

with a low transverse incision either due to trauma or

other non-incisional causes, and perinatal death due to

lethal anomaly versus intolerance or management of

labor.

• Standard terminology. In order to accurately measure

outcomes, there must be a consistent terminology. Lack

of this prevents accurate and meaningful comparisons of

risks for each delivery choice. Outcomes such as

infection, hemorrhage, and uterine rupture were not

consistently defined. 

• Separating prevention/prediction strategies from

outcomes. As long as potentially important predictors of

events such as prolonged fetal bradycardia as a predictor

for clinically significant uterine rupture are included in

the definition of uterine rupture, their true value as a

predictor rather than a confounder will remain unknown.

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-inmotion studies would help to estimate these costs.

Availability of the 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. It is expected to be

available in the winter 2003. At that time, printed copies may

be obtained free of charge from the AHRQ Publications

Clearinghouse by calling 800-358-9295. Requesters should ask

for Evidence Report/Technology Assessment No. 71, Vaginal

Birth After Cesarean (VBAC). In addition, Internet users will

be able to access the report and this summary online through

AHRQ’s Web site at www.ahrq.gov.

AHRQ Pub. No. 03-E017

March 2003

ISSN 1530-440X