Executive Summary

Publication Details


Despite the Healthy People 2010 national goal1 to reduce the cesarean delivery rate to 15 percent of births each year, this century has set record rates of cesarean deliveries. When the national rate of cesarean delivery was first measured in 1965, it was 4.5 percent,2 in 2007, almost one in three women in the United States (U.S.) delivered by cesarean (32.8 percent cesarean delivery rate in 2007). With almost 1.5 million cesarean surgeries performed every year, cesarean is the most common surgical procedure in the U.S. Vaginal birth after cesarean (VBAC) emerged from the 1980 National Institutes of Health (NIH) Consensus Conference on Cesarean as a mechanism to safely reduce the cesarean delivery rate.3 VBAC proved to be an effective contributor to reduce the use of cesarean through the early 1990s. From 1990 through 1996, the VBAC rate rose from 19.9 to 28.3 percent and the cesarean rate declined from 22.7 to 20.7 percent.4 Since 1996, VBAC rates have declined sharply, to the point where over 90 percent of women with a prior cesarean will deliver by repeat cesarean. While primary cesarean accounts for the largest number of cesarean deliveries, the largest single indication for cesarean is prior cesarean accounting for 534,180 cesareans each year, thus the safety of VBAC remains important.1 The degree to which cesarean deliveries and VBACs are improving or adversely affecting health remains a subject of continued controversy and uncertainty. This systematic review was conducted to inform the 2010 NIH Consensus Development Conference to evaluate emerging issues relating to VBAC.

Key Questions

The key questions reviewed in this report were assigned by the Agency for Healthcare Research and Quality. Questions were based on deliberations of the planning committee for the National Institutes of Health Consensus Development Conference on Vaginal Birth After Cesarean: New Insights convened by the National Institutes of Health’s Office of Medical Applications of Research and further refined by a technical expert panel during the evidence report process. Ultimately, four key questions were reviewed for this report:

  1. Among women who attempt a trial of labor after prior cesarean, what is the vaginal delivery rate and the factors that influence it?
  2. What are the short- and long-term benefits and harms to the mother of attempting trial of labor after prior cesarean versus elective repeat cesarean delivery, and what factors influence benefits and harms?
  3. What are the short- and long-term benefits and harms to the baby of maternal attempt at trial of labor after prior cesarean versus elective repeat cesarean delivery, and what factors influence benefits and harms?
  4. What are the critical gaps in the evidence for decision-making, and what are the priority investigations needed to address these gaps?


Relevant studies were identified from multiple searches of MEDLINE®; DARE; the Cochrane databases (1966 to September 2009); and from recent systematic reviews, reference lists, reviews, editorials, Web sites, and experts. Retrieved abstracts were entered into an electronic database (EndNote®).

Of the 3,134 citations reviewed from the searches, 2,171 met exclusion criteria at the abstract level and were not reviewed further. After the abstract review process, 963 full-text papers were retrieved and reviewed for inclusion. An additional 37 full-text papers were retrieved from peer review. A total of 203 full-text papers met inclusion after applying paper inclusion/exclusion criteria. Investigators quality rated included studies, and those rated good or fair quality are discussed in this report. For the topics presented, 71 studies provided data on trial of labor (TOL) and VBAC rate, 27 on induction of labor (IOL) or augmentation, 28 on predictors of TOL and VBAC, 14 on scored models for predicting VBAC, 41 on maternal outcomes, 11 on infant outcomes, 28 on uterine rupture, 19 on abnormal placentation, seven on obesity, 12 on multiple cesarean deliveries, and seven on direction of cesarean delivery scar.


Among women who attempt a trial of labor after prior cesarean, what is the vaginal delivery rate and the factors that influence it?

Who attempts a trial of labor? The rates of TOL are highly variable, ranging from 28 to 70 percent with an overall rate of 58 percent in the U.S. The evidence is largely limited to large tertiary teaching hospitals. TOL rates have declined, particularly after 1996, both inside and outside of the U.S. In the U.S. studies that initiated enrollment after 1996, less than half (47 percent) of women had a TOL. TOL is more likely in hospitals with higher delivery volumes, tertiary care centers, and teaching hospitals. Women with a prior vaginal delivery or non-white women were more likely to have a TOL (odds ratio 1.51 to 6.67 and odds ratio 3.5, respectively).

What is the vaginal delivery rate? In 43 U.S. based studies, 74 percent of women who had a TOL delivered vaginally. While TOL rates reported in observational studies have dropped over time, VBAC rates have remained constant for the women who have a TOL.

What are the factors that influence the vaginal delivery rate? All scored predictive models provide reasonable ability to identify women who are good candidates for VBAC, but none have discriminating ability to consistently identify women who are at risk for cesarean delivery.

Antepartum factors

Prior vaginal delivery: A prior history of vaginal delivery was consistently reported to increase likelihood of VBAC approximately three fold (range odds ratio 1.83 to 28). Among women requiring induction of labor, limited evidence also suggests a higher rate of VBAC among those with prior vaginal delivery (OR 6.8; 95 percent CI: 3.04 to 13.9).

Indication for prior cesarean: Women with prior cesarean delivery for malpresentation/breech were more likely to have a VBAC (75 percent, range 60 to 86 percent) compared with women with prior cesarean delivery for fetal distress (60 percent, range 49 to 69 percent) or failure to progress/cephalopelvic disproportion (54 percent, range 48 to 60 percent).

Race: Hispanic and African American women were more likely to have a TOL but less likely to have a VBAC compared with non-Hispanic and white women, respectively (20 to 49 percent).

Location: Women at rural and private hospitals had a decreased likelihood of TOL and a decreased likelihood of VBAC (57 percent versus 66 percent for tertiary care centers).

Macrosomia: There was decreased likelihood of VBAC in infants weighing 4,000 grams or greater (odds ratio 0.62; 95 percent CI: 0.54 to 0.71). Infants weighing 4,500 grams or greater were less likely to be delivered via VBAC (1.3 to 5.8 percent) compared with 4,000 to 4,499g infants (11.6 to 17.4 percent).

Body mass index: VBAC rates ranged from 68 to 77 percent in the studies of obese women. Women with a body mass index (BMI) of less than 40 had VBAC rates of 52.1 to 70 percent.

Intrapartum factors

Progress of labor: A greater progress of labor--as determined by more advanced dilation, lower station, and higher Bishop score--predicted a higher likelihood of VBAC.

Epidural: The effect of epidural use on the likelihood of VBAC is uncertain.

Augmentation: Augmentation of labor with oxytocin was associated with a rate of 68 percent VBAC, although the strength of this evidence was low.

Induction: Sixty-three percent of women with IOL had a VBAC (PGE2=63 percent, oxytocin=62 percent, misoprostol=61 percent). Fifty-four percent of women induced with a Foley Catheter had a VBAC.

What are the short- and long-term benefits and harms to the mother of attempting trial of labor after prior cesarean versus elective repeat cesarean delivery, and what factors influence benefits and harms?

What are the short-term benefits and harms to the mother of TOL versus elective repeat cesarean delivery (ERCD)?

Maternal death. While maternal mortality is rare, with an overall rate of 10.1 per 100,000 for all women with prior cesarean, the risk of maternal mortality is significantly increased with ERCD (3.8 per 100,000 for TOL versus 13.4 per 100,000 ERCD). When limited to term studies, the maternal mortality was 1.9 per 100,000 for TOL and 9.6 per 100,000 for ERCD.

Hysterectomy. Hysterectomy was rare, occurring in less than three percent of all women with prior cesarean. There was no significant difference between the TOL and ERCD with respect to hysterectomy among all studies or when studies were limited to term populations; however hysterectomy was more common among women undergoing ERCD among studies that were open to all gestational ages (GAs).

Transfusion/hemorrhage. When limited to term studies, the rate of transfusion for TOL was 6.6 per 1,000 (95 percent CI: 2.0 to 22.1 per 1,000) and for ERCD was 4.6 per 1,000 (95 percent CI: 1.6 to 13.2 per 1,000). In term patients, TOL is associated with increased risk of transfusion. When all GAs are evaluated, there is an increased risk of transfusion with ERCD, suggesting a risk-modifying effect of preterm delivery on risk of transfusion. In low risk ERCD, there was a statistically significant increase in transfusion with TOL compared with ERCD prior to labor. Spontaneous labor may be protective against hemorrhage, but data are inconsistent.

Infection. For any GA cohorts, the risk for any infection with TOL was 46 per 1,000 (95 percent CI: 15 to 135 per 1,000) and for ERCD was 32 per 1,000 (95 percent CI: 13 to 73 per 1,000). The rate for fever with TOL was 65 per 1,000 (95 percent CI: 44 to 93 per 1,000) and for ERCD was 72 per 1,000 (95 percent CI: 25 to 189 per 1,000). Studies that did not report TOL outcome (VBAC or repeat cesarean delivery [RCD] after a TOL) tend to report increased febrile morbidity associated with TOL. Cesarean delivery, either ERCD or RCD after a TOL, appears to have a higher incidence of any febrile morbidity compared with VBAC but definitive studies are lacking. A trend toward increased endometritis was seen with ERCD compared with TOL; in contrast, chorioamnionitis was increased in TOL compared with ERCD. Increasing BMI was associated with increased fever in patients undergoing TOL.

Surgical injury. Rate of surgical injury may be increased with TOL, but definitive studies are lacking. Vertical skin incision increases risk of surgical injury to the bladder.

Length of stay. Elective repeat cesarean delivery is associated with a longer hospital stay compared with TOL. The mean length of stay for TOL was 2.55 days (95 percent CI: 2.34 to 2.76 days) compared with 3.92 days (95 percent CI: 3.56 to 4.29) for ERCD.

Uterine rupture. The risk of uterine rupture for all women with a prior cesarean delivery regardless of route of delivery is 0.3 percent (95 percent CI: 0.2 to 0.4 percent). The risk of uterine rupture for women undergoing a TOL is significantly elevated at 0.47 percent (95 percent CI: 0.28 to 0.77 percent); compared with women undergoing an ERCD (0.026 percent; 95 percent CI: 0.009 to 0.082 percent).

Maternal morbidity. To date, there have been no maternal deaths reported because of uterine rupture. The risk of hysterectomy due to uterine rupture ranged from 14 to 33 percent.

Neonatal morbidity. The overall risk of perinatal death due to uterine rupture was 6.2 percent. The two studies of women delivering at term that reported perinatal death rates report that 0 to 2.8 percent of all uterine ruptures resulted in a perinatal death. Overall, the literature relating to response time between premonitory signs of uterine rupture and perinatal mortality are insufficient. However, there is suggestion that fetal bradycardia is an ominous sign for fetal extrusion, which is associated with poor perinatal outcomes, and prompt delivery in this setting is warranted.

What factors influence the incidence of uterine rupture?

Direction of scar. Women with a prior classical incision are at increased risk of uterine dehiscence/rupture. Compared with women with prior low transverse cesarean delivery (LTCD), women with prior low vertical cesarean delivery (LVCD) or with an unknown scar are not at a significantly increased risk of uterine dehiscence or rupture.

Induction of labor. The risk of rupture with any IOL method at term was 1.5 percent and 1.0 percent when any GA was considered. At greater than 40 weeks, the rate was highest at 3.2 percent.

Gestational age. Relative to women with spontaneous labor, there was no increase in risk of rupture among those induced at term. Women induced after 40 weeks GA had an increased risk compared with those undergoing spontaneous labor (risk difference 1.8 percent; 95 percent CI: 0.1 to 3.5 percent, NNH 56).

Method of induction. The rate of uterine rupture by induction method--oxytocin, PGE2, and misoprostol--was 1.1 percent, two percent, six percent, respectively. The risk of uterine rupture with mechanical methods of IOL is understudied.

Can uterine rupture be predicted? Studies of individual factors that may increase or decrease a woman’s risk of uterine rupture are largely exploratory.

Protective factors. Women with prior vaginal delivery have lower risk for uterine rupture.

Risk factors. Women undergoing IOL have higher risk of uterine rupture compared with spontaneously laboring women. Women who are postdate may have a higher risk of uterine rupture. Obese and morbidly obese women are more likely to suffer rupture and/or dehiscence. Women with a prior classical incision are at increased risk of uterine rupture.

Predictive measures. No study was able to produce a reliable and robust model to predict uterine rupture. This is likely because uterine rupture is a rare event, and although there are factors associated with uterine rupture, none are of great magnitude. An accurate and reliable tool to predict an individual woman’s risk of uterine rupture has not been found.

Imaging. The data regarding ultrasound measurements of uterine thickness and uterine rupture consistently suggest that there may be value to ultrasound measurements of uterine thickness for women with prior cesarean delivery.

What are the long-term benefits and harms to the mother of TOL versus ERCD?

Adhesions. Prior cesarean delivery was associated with a statistically significant increase in adhesions at subsequent cesarean and hysterectomy. Adhesions were associated with increased perioperative complications, time to delivery, and total operative time. It is unclear whether adhesions and complications increase with increasing number of prior cesareans.

General health. No studies evaluated TOL and/or RCD with respect to pelvic pain, risk of ectopic pregnancy, and general health risks, such as diabetes or high blood pressure.

Fertility. Two studies have shown impaired fertility following cesarean delivery. One study found a difference in the ability to conceive in subjects undergoing cesarean delivery compared with instrumented vaginal delivery (odds ratio 0.33; 95 percent CI: 0.12 to 0.98). Another study found a history of cesarean delivery was associated with increased odds of taking greater than 1 year to conceive (odds ratio 1.53; 95 percent CI: 1.09 to 2.14).

Menopause. One case-control study found an increased risk of early menopause in women with multiple cesarean deliveries compared with no pelvic surgery (odds ratio 2.69; 95 percent CI: 1.16 to 6.22).

What are the long-term benefits and harms to the mother of multiple cesarean? Women who do not have a TOL will undergo RCD and, potentially, multiple cesareans.

Hemorrhage/transfusion. The overall rates of hemorrhage/transfusion with multiple cesarean deliveries were less than five percent, but the risk appeared to increase with increasing numbers of cesareans.

Adhesions. The incidence of adhesions increased with increasing numbers of cesareans.

Surgical injury. Bladder, bowel, and ureteral injury are uncommon occurrences that appear to increase with multiple cesareans.

Infection. The risk of postoperative infection with multiple cesareans remains unclear.

Wound complications. The risk of wound complications does not appear to increase with multiple cesarean deliveries.

Hysterectomy. There was a strong correlation between multiple cesareans and hysterectomy. The odds ratio for hysterectomy with one prior cesarean was 0.7 to 2.14, with one or more was 1.4 to 7.9, and two or more was 3.8 to 18.6.

Abnormal placentation

Abruption. The risk of abruption for women with any prior cesarean was 0.10 to 0.15 percent. The risk did not appear to increase with prior cesarean or number of prior cesarean deliveries.

Previa. Women with a prior cesarean delivery had a statistically significant increased risk of placenta previa compared with women with no prior cesarean at a rate of 12 per 1,000 (95 percent CI: 8 to 15 per 1,000). The incidence increased with increasing number of prior cesarean deliveries. Prior cesarean was a significant risk factor for maternal morbidity in women with previa. Compared with previa patients without a prior cesarean delivery, women with one prior cesarean and previa had a statistically significant increased risk of blood transfusion (15 versus 32.2 percent), hysterectomy (0.7 to 4 percent versus 10 percent), and composite maternal morbidity (15 versus 23 to 30 percent). For women with three or more prior cesarean deliveries and previa, the risk of hysterectomy and composite maternal morbidity rose significantly (0.7–4 percent versus 50–67 percent and 15 versus 83 percent, respectively).

Accreta. The incidence of placenta accreta rose with increasing number of prior cesarean deliveries. The results were statistically significant for women with two or more prior cesareans (odds ratio 8.6 to 29.8).

Previa and accreta. Women with placenta previa are at increased risk for placenta accreta, and the risk increased with increasing number of prior cesareans. Women with more than three prior cesareans and previa had a 50–67 percent incidence of accreta.

What are the short- and long-term benefits and harms to the baby of maternal attempt at trial of labor after prior cesarean versus elective repeat cesarean delivery, and what factors influence benefits and harms?

What are the short-term benefits and harms to the baby of maternal attempt at TOL versus ERCD?

Perinatal death. Perinatal, fetal, and neonatal mortality rates were low in women with a history of prior cesarean delivery. The overall perinatal death rate with TOL was 1.3 per 1,000 (95 percent CI: 0.59 to 3.04 per 1,000) compared with 0.5 per 1,000 (95 percent CI: 0.07 to 3.82 per 1,000) for ERCD. The intrapartum death rates were consistently slightly higher in women who attempt a TOL (0.1 to 0.4 per 1,000) versus ERCD (0 to 0.04 per 1,000). Women with high-risk conditions and indicated repeat cesarean delivery (IRCD) appear to have higher rates of neonatal mortality.

Sepsis. Three studies measured sepsis in the neonate undergoing a TOL versus ERCD; however only one study actually defined and measured “proven” sepsis. This study found no differences in proven sepsis in infants born after TOL versus those delivered by ERCD.

Apgar scores. Four studies found no differences in Apgar scores of less than six and seven at 5 minutes in infants undergoing a TOL versus ERCD. Three studies examined the differences in low Apgars (less than seven) at 5 minutes in VBAC versus RCD after a TOL; two of these studies found no difference in Apgar scores of infants born by VBAC versus RCD after a TOL.

Neonatal intensive care unit (NICU) admission. Six of eight studies found no significant differences in frequency of NICU admissions between TOL and ERCD.

Breastfeeding. No studies were found that explored the effect of a TOL versus an ERCD on breastfeeding initiation or continuation.

Additional short-term outcomes. There was insufficient evidence to determine if rates of respiratory distress, neonatal trauma, or asphyxia/hypoxic-ischemic encephalopathy varied between TOL and ERCD.

Factors related to outcomes. There was insufficient data to determine that fetal presentation or gestational age in term neonates influences benefits or harms to the neonate undergoing TOL versus ERCD.

What are the long-term benefits and harms to the baby of maternal attempt TOL versus ERCD?

Perinatal outcome in future pregnancies. One study showed that prior cesarean delivery increases the risk for unexplained stillbirth in the next pregnancy and another study showed no difference in risk for stillbirth. Both studies are limited by their retrospective design and relied on large perinatal databases while employing various methodologies to overcome confounding.

Neurological development. No studies were found that measured the impact of a TOL versus ERCD on neonatal neurological development.


While cesarean deliveries represent a third of all births, they account for almost half of the childbirth-related expenses of hospitalization, at $7.8 billion annually.1 A major contributor to the increase in cesareans is the rapid decline in VBACs witnessed over the last decade. Therefore, the appropriate and safe use of cesarean and VBAC is not only an individual patient- and provider-level concern, but it is also a national health policy concern.

One of the major findings of this report is that the best evidence suggests that VBAC is a reasonable and safe choice for the majority of women with prior cesarean. The occurrence of maternal and infant mortality for women with prior cesarean is not significantly elevated when compared with national rates overall of mortality in childbirth. The majority of women who have TOL will have a VBAC, and they and their infants will be healthy. However, there is a minority of women who will suffer serious adverse consequences of both TOL and ERCD. While TOL rates have decreased over the last decade, VBAC rates and adverse outcomes have not changed suggesting that the reduction is not reflecting improved patient selection. Sophisticated statistical models have not been able to predict those women who will do well and those who will be harmed.

The most dramatic change since the 1980 VBAC report is the number of women with multiple cesareans. This report found that women with three or more prior cesareans are at significantly increased risk of complications, and the risks increase for women with prior cesarean delivery and previa. Since we are unable to determine which women will have previa or to prevent its occurrence, all pregnant women are at risk, and the risk increases with multiple cesareans.

Studies of VBAC versus ERCD have traditionally reported outcomes based upon actual route of delivery rather than intended route, leading to misclassification of patients who intend elective repeat cesarean but go into labor prior to their cesarean or women who intended trial of labor but who are delivered by cesarean. The evidence from these studies is at best indirect and difficult to apply to a woman who plans for either option. Each leaves clinicians and patients uncertain of the ramification for their decisionmaking and masks potential adverse effects of desiring one route of delivery but having another.

Mode of delivery for subsequent pregnancies poses a difficult question for women with prior cesarean and their providers. Some women have already made their decision prior to leaving the hospital after their cesarean, due to factors surrounding that birth. Others will decide early in pregnancy, and still others will remain undecided until presenting in labor. Some women will not have a choice due to provider, hospital, insurance, or medico-legal factors that mandate repeat cesarean. This report suggests that although there are statistically significant differences between ERCD and TOL, there are very few clinically significant differences, and the overall mortality risk is not significantly elevated between women with prior cesarean delivery and women undergoing their first pregnancy. Serious deficiencies were found in the existing literature, however, and this report provides a list of research priorities as prioritized by national experts as well as potential study designs to advance the field and provide important information to patients, clinicians, and policymakers.