Vaginal Birth After Cesarean Delivery

Author: Aaron B Caughey, MD, PhD, MPH, MPP, Associate Professor in Residence, Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, University of California at San Francisco; Medical Director of Diabetes and Pregnancy Program, Director of Perinatal Research, Program Director of Maternal-Fetal Medicine Fellowship, University of California at San Francisco

Introduction

"Once a cesarean, always a cesarean." From the time they were spoken in 1916 to the New York Association of Obstetricians & Gynecologists over the ensuing 50-60 years, these words reflected most of US obstetricians' management of patients with a prior cesarean delivery . By 1988, the overall cesarean delivery rate was 25%, rising from less than 5% in the early 1970s. Only 3% of live-born infants were delivered vaginally after the mother had undergone a prior cesarean delivery.

Although attempts at a trial of labor after a cesarean birth have become accepted practice, the rate of successful vaginal birth after cesarean delivery (VBAC), as well as the rate of attempted VBACs, has decreased during the past 10 years. Whereas, 40-50% of women attempted VBAC in 1996, as few as 20% of patients with a prior cesarean delivery attempted a trial of labor in 2002. This number is drifting down toward the 10% mark with fewer than 10% of women achieving successful VBAC in 2005.

Several factors have contributed to this decline. As practitioners experience complications related to managing patients undergoing trials of labor after cesarean delivery, they are less likely to allow new patients to undergo a trial of labor. In addition, 1999 guidelines from the American College of Obstetricians and Gynecologists (ACOG) clearly state that patients undergoing a trial of labor after cesarean delivery require the presence of an obstetrician, an anesthesiologist, and/or a staff capable of performing an emergency cesarean delivery throughout the patient's active phase of labor.1 While academic centers and larger community hospitals readily comply with this requirement, many smaller hospitals do not offer in-house anesthesia or obstetric staff. Furthermore, to meet the financial demands of managed care, many obstetricians now cover more than one hospital simultaneously, making it difficult to meet the ACOG guidelines.

The impact of these changes can be observed in national birth statistics. The cesarean delivery rate peaked at 25% in 1988, but then declined to 21% overall in 1996. However, from 1996-2004, the cesarean delivery rate increased to 29.2%, while the rate of VBAC declined from 28% to 9%. Assuming an overall 70% VBAC success rate, this correlates with a decline of 40% to 14% in the number of patients with a prior cesarean birth choosing to undergo a trial of labor. What once was hailed as a key component of lowering the overall cesarean birth rate (ie, trial of labor in patients with previous cesarean birth) is losing the support it had in the 1980s. Overall, this has led to a rate of cesarean delivery of 31.1% in 2006, the highest rate in US history, with no signs of decreasing.

When considering which patients should be offered a trial of labor after cesarean delivery, compliance with ACOG recommendations must be ensured. Once compliance is established, patients should be routinely counseled early in the pregnancy regarding the risks and benefits of a trial of labor. Many obstetric practices and healthcare institutions have adopted a separate consent form for patients wishing to attempt a VBAC. While consent helps to formalize counseling, documentation of the overall risks quoted to the patient, specifically mentioning the individual's risk factors, is all that is truly necessary. However, because of medical-legal concerns, formalized written consent forms, and even video-taped counseling-consent interactions, are used by clinicians around the United States.

Two specific outcomes of interest regarding a trial of labor after cesarean delivery have been well investigated: successful VBAC and uterine rupture. Other outcomes are certainly of interest, including neonatal outcome, hysterectomy, and maternal mortality; however, few studies have focused on these outcomes, and poor outcomes occur too rarely to be well represented in established databases.

In earlier studies, most outcomes were reported after univariate analysis. Risk factors were examined without controlling for potential confounding variables, and results were reported as a relative risk or odds ratio. These ratios represent the risk of the group of individuals who have the risk factor divided by individuals without the risk factor. Over the last decade, several large cohorts have examined predictors and outcomes related to women with a prior cesarean delivery. These studies have ranged from Nova Scotia to Boston to the state of Washington. Finally, 2 large multicenter studies have been publishing multiple studies on this issue, one out of Pennsylvania and the other out of the Maternal-Fetal Medicine Units. These large studies over the last decade have used multivariate statistics to examine risk factors. This means that other risk factors and confounding factors, such as birthweight, maternal age, obstetric history, and labor management, were controlled for in the analysis. In this article, factors associated with mode of delivery in the setting of a trial of labor and factors associated with uterine rupture in this same setting are reviewed.

For excellent patient education resources, visit eMedicine's Pregnancy and Reproduction Center . Also, see eMedicine's patient education article Labor Signs .

Predictors of a Successful Trial of Labor

The predictors of a successful trial of labor after cesarean delivery are extensively described in the existing literature (see Table 1). While no randomized trials have been conducted, relatively large databases have been analyzed (using both univariate and multivariate techniques) to determine risk factors for patients undergoing a trial of labor after cesarean delivery. In addition, several scoring systems have been devised to help predict which patients are likely to be successful when attempting a vaginal birth after cesarean delivery (VBAC).

Because no large, prospective, randomized, controlled trials have been conducted, most of the risk factors have been determined from retrospective cohort and case-control studies. These studies have been increasingly analyzed with multivariate techniques, allowing for control of confounding factors. However, control for physician practice is difficult, and physician practice can greatly impact the strength of the association between these risk factors and a successful VBAC. Even when controlling for demographic data, obstetric history, birthweight, gestational age, induction of labor, and other variables, the bias inherent in nonrandomized and nonblinded trials cannot be eliminated.

Table 1: Predictors of VBAC Success or Failure

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Table
Increased Chance of Success
 
Decreased Chance of Success
 
Prior vaginal delivery
 
Maternal obesity
 
Prior VBAC
 
Short maternal stature
 
Spontaneous labor
 
Macrosomia
 
Favorable cervix
 
Increased maternal age (>40)
Nonrecurring indication (breech, previa, herpes)
 
Induction of labor
 
Preterm delivery
 
Recurring indication (cephalopelvic disproportion [CPD], failed second stage)
  Increased interpregnancy weight gain
  Latina or African-American race/ethnicity
  Gestational age ≥ 41 weeks
  Preconceptional or gestational diabetes mellitus
Increased Chance of Success
 
Decreased Chance of Success
 
Prior vaginal delivery
 
Maternal obesity
 
Prior VBAC
 
Short maternal stature
 
Spontaneous labor
 
Macrosomia
 
Favorable cervix
 
Increased maternal age (>40)
Nonrecurring indication (breech, previa, herpes)
 
Induction of labor
 
Preterm delivery
 
Recurring indication (cephalopelvic disproportion [CPD], failed second stage)
  Increased interpregnancy weight gain
  Latina or African-American race/ethnicity
  Gestational age ≥ 41 weeks
  Preconceptional or gestational diabetes mellitus


Maternal characteristics

Several studies examine prepregnancy weight and height to examine the effect on mode of delivery. Not surprising, women who are shorter and women who are obese are more likely to undergo cesarean delivery. Of note, not only increased prepregnancy weight, but increased gestational weight gain has been associated with cesarean delivery. In the setting of trial of labor after cesarean delivery, an increasing number of studies exist, all of which show that women in the morbidly obese range have a higher risk of failing a trial of labor. Interpregnancy weight gain has been shown to increase the risk of failure in a subsequent trial of labor, but unfortunately, interpregnancy weight loss has not demonstrated an improvement in VBAC success.

Maternal age has also been examined in several studies in VBAC literature. Adjusting for confounding factors, women older than 40 years who have had a prior cesarean delivery have an almost 3-fold higher risk for a failed trial of labor compared with women younger than 40 years. In one scoring system, women younger than 40 years were given an extra point as a predictor for successful VBAC.2

Maternal race and ethnicity have been examined as a predictor for VBAC in the setting of trial of labor and have not generally been noted to be a strong predictor. However, in the recent Maternal-Fetal Medicine Unit (MFMU) Cesarean Registry, both Hispanic ethnicity (odds ratio [OR] 0.65; 95% confidence interval [CI], 0.59-0.72) and African American ethnicity (OR 0.69; 95% CI, 0.63-0.75) were associated with lower rates of successful trial of labor. Whether this is due to actual biologic reasons or rather ethnicity acting as a proxy for some other factor or factors remains to be elucidated.

Birth weight

Birth weight greater than 4000 g is associated with an almost 4-fold higher risk of cesarean birth among nulliparous women (OR, 2.3-3.7). Several studies have demonstrated a difference in VBAC rates between patients with a birth weight greater than 4000 g and those with a lower birth weight. The odds ratio for this risk factor ranges from 1.2-1.9. Consistent with these findings, several studies have demonstrated a higher failure of a trial of labor with increasing birth weight.

Obstetric history

Obstetric history is enormously important in terms of risk factors for a successful trial of labor. Predictors for increased success include a nonrecurring indication for prior cesarean delivery (eg, breech presentation, placenta previa) and prior vaginal delivery. A history of cephalopelvic disproportion (CPD), failure to progress, no prior vaginal deliveries, or a prior cesarean delivery performed in the second stage of labor are negative predictors of success in a subsequent trial of labor.

Indications for prior cesarean delivery

Several studies have examined indications for prior cesarean delivery as a predictor of outcome in a subsequent trial of labor. In all studies, CPD had the lowest VBAC success rate (60-65%). Fetal distress (eg, nonreassuring fetal testing) had the second lowest success rate of VBAC (69-73%). Nonrecurrent indications, such as breech birth, herpes, and placenta previa, were associated with the highest rates of success (77-89%). Failure to progress, CPD, or dystocia as indications for prior cesarean delivery are also associated with a higher proportion of patients not attempting a trial of labor after cesarean birth. In a meta-analysis of the existing literature prior to 1990, Rosen et al demonstrated that women whose prior cesarean delivery was performed for CPD were twice as likely to have an unsuccessful trial of labor.3

Prior vaginal delivery

Patients with a prior vaginal delivery have higher rates of successful VBAC compared with patients without a prior vaginal birth. Furthermore, women with a successful VBAC have a higher success rate in a subsequent trial of labor compared with women whose vaginal delivery was prior to cesarean delivery. In an unadjusted comparison, patients with 1 prior vaginal delivery had an 89% VBAC success rate compared with a 70% success rate in patients without a prior vaginal delivery. In comparisons controlling for confounding factors, odds ratios of 0.3-0.5 for rate of cesarean delivery are found when comparing patients with a prior vaginal delivery with those without prior vaginal delivery. Among patients with a prior VBAC, the success rate is 93% compared with 85% in patients with a vaginal delivery prior to their cesarean birth but no prior VBAC. These findings have been repeatedly validated by multiple studies.

See Medscape CME activity Prior Successful Vaginal Birth After Cesarean Delivery Linked to Low Risk for Complications in Later Attempts .

Cervical dilation at prior cesarean delivery

Only one study carefully examines cervical dilation at prior cesarean delivery. In this study, the degree of cervical dilation in the prior delivery is directly associated with the likelihood of success in the subsequent trial of labor. For example, 67% of patients who were dilated 5 cm or less at the time of their delivery had a successful VBAC compared with 73% of patients who were dilated 6-9 cm. The success rate is much lower for patients whose labor arrested in the second stage; only 13% of patients who were fully dilated at the time of their prior delivery had a successful VBAC. In a similar study, patients who had their prior cesarean delivery in the first stage of labor had a lower rate of cesarean delivery than those who had their prior cesarean delivery in the second stage of labor. However, in this study, 66% of patients who had a cesarean delivery for dystocia in the second stage had a successful VBAC.

Induction of labor

Patients who undergo induction of labor are at a higher risk of cesarean delivery compared with women who experience spontaneous labor. This finding has also been observed in women with a prior cesarean delivery. Several studies have demonstrated that women who are induced in a trial of labor after cesarean delivery have a 2- to 3-fold increased risk of cesarean delivery compared with those who present with spontaneous labor. A recent study demonstrated that patients who were able to be induced with oxytocin had a significantly lower cesarean delivery rate compared with those induced with a Foley bulb.

Gestational age

Similar to studies of mode of delivery and gestational age in women without a prior cesarean delivery, increasing gestational age is associated with a decreased rate of successful VBAC. Three potential factors are related to the association of increasing gestational age with an increased rate of cesarean delivery: increasing birth weight, increased risk of fetal intolerance of labor, and increased need for induction of labor. However, in a recent study that controlled for both birth weight and induction/augmentation of labor, gestational age of greater than 41 weeks was still associated with failed VBAC.

Cervical examination on admission

Not surprisingly, patients who present to labor and delivery with advanced cervical examination findings have a greater success rate of vaginal birth. Several components of the cervical examination have been investigated, including cervical dilation and cervical effacement. Not surprisingly, the more advanced the cervical examination finding is upon initial presentation, the higher the rate of successful VBAC. A 1997 Flamm et al study demonstrated that patients presenting with dilation greater than or equal to 4 cm had an 86% rate of VBAC.

Interpregnancy interval

The timing between pregnancies has recently become an interesting predictor for a number of obstetric outcomes, VBAC success among them. In one analysis, women who had an interpregnancy interval of more than 18 months had an 86% chance of VBAC success, while women whose interpregnancy interval was less than 18 months had a VBAC success rate of 79%. This difference was not statistically significant, and whether interpregnancy interval does have any effect on success or rather only has an effect on the risk for uterine rupture is unclear.

Preterm delivery

Preterm labor and delivery is one of the factors that deserves attention as it should be considered an opportunity to recounsel women about the risks and benefits of a trial of labor after cesarean delivery. In one large study by Quinones et al, 12,463 attempted a trial of labor and the VBAC success rates for the term and preterm groups were 74% and 82%, respectively (P < .001) with an aOR of 1.54 (95% CI 1.27-1.86) for preterm delivery. Additionally, a trend toward decreased risk of uterine rupture among preterm delivery gestations was also found (aOR 0.28, 95% CI 0.07-1.17).4 These data can certainly be used to counsel women with a prior cesarean who are in preterm labor.

Gestational or pregestational diabetes

Only one study of patients undergoing a trial of labor after cesarean delivery has examined the rate of success in patients with diabetes mellitus (DM). This study demonstrated that patients with either gestational DM or pregestational DM had a lower rate of successful trial of labor. This is not particularly surprising; however, further studies are needed to sort out the differences between gestational and pregestational DM and the interaction between DM and birth weight.

Risk Factors for Uterine Rupture

One of the most significant risks women face when considering a trial of labor is that of uterine rupture. This potentially fatal event may have significant maternal and neonatal sequelae. A threshold of acceptable risk has been established between risk of women with 1 prior cesarean delivery (0.5-1%) and women with a history of a prior classic cesarean delivery (6-12%). These latter patients, along with women who have had metroplasty surgery for uterine anomalies or myomectomies that have entered the uterine cavity, are discouraged from attempting a VBAC. Other patients who are at increased risk for uterine rupture include those who have had 2 or more hysterotomies, those who are treated with prostaglandin agents, and those undergoing induction of labor (see Table 2 ).

Table 2: Predictors of Uterine Rupture

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Table
Increased Rate of Uterine Rupture
 
Decreased Rate of Uterine Rupture
 
Classical hysterotomy
 
Spontaneous labor
 
Two or more cesarean deliveries
 
Prior vaginal delivery
 
Single-layer closure
 
Longer interpregnancy interval
 
Induction of labor Preterm delivery
 
Use of prostaglandins  
 
Short interpregnancy interval  
 
Infection at prior cesarean delivery  
Increased Rate of Uterine Rupture
 
Decreased Rate of Uterine Rupture
 
Classical hysterotomy
 
Spontaneous labor
 
Two or more cesarean deliveries
 
Prior vaginal delivery
 
Single-layer closure
 
Longer interpregnancy interval
 
Induction of labor Preterm delivery
 
Use of prostaglandins  
 
Short interpregnancy interval  
 
Infection at prior cesarean delivery  


Classical hysterotomy

Unquestionably, practitioners do not feel safe allowing a patient who has had a prior classical hysterotomy (ie, a vertical incision that has extended above the insertion of the round ligaments) to undergo a trial of labor. Patients with a prior classical hysterotomy have a higher rate of uterine rupture in subsequent pregnancies. Because these patients can sustain a uterine rupture prior to labor, they are often delivered at 36-37 weeks' gestation. Although available data are limited, the risk of uterine rupture in this group of patients is estimated at 6-12%.

Low vertical (Krönig) hysterotomy

Retrospective cohort studies have demonstrated that the risk of uterine rupture is no greater for patients who have had a vertical incision in the lower uterine segment than those who have had a transverse incision. The rate of uterine rupture from these studies is 0.8-1.3%. When comparing patients with prior Krönig hysterotomies to patients with low transverse incisions, no statistical difference exists in either univariate or multivariate analyses controlling for the confounding factors of obstetrical history, induction of labor, birth weight, and length of labor.

Low transverse (Kerr) hysterotomy

Most babies delivered abdominally are delivered through a transverse incision in the lower uterine segment (Kerr hysterotomy). In several large retrospective cohort studies, the reported rate of uterine rupture is 0.3-1% (see Table 3 ). Rates of 0.5-1% (1 in 200 to 1 in 100) are commonly used to counsel patients with no other additional risk factors.

 

Table 3: Rates of Uterine Rupture

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Table
Study
 
Sample Size (N)
 
Rates
 
Miller, 1994
 
10,880
 
63 uterine ruptures (0.6%)*
 
Flamm, 1994
 
5,022
 
39 uterine ruptures (0.8%)
 
McMahon, 1996
 
3,249
 
10 uterine ruptures (0.3%)
 
Shipp, 1999
 
2,912
 
28 uterine ruptures (1%)
 
Landon, 2004
 
17,898
 
124 uterine ruptures (0.7 %)
 
Macones, 2005 13,331 128 uterine ruptures (0.9%)
Study
 
Sample Size (N)
 
Rates
 
Miller, 1994
 
10,880
 
63 uterine ruptures (0.6%)*
 
Flamm, 1994
 
5,022
 
39 uterine ruptures (0.8%)
 
McMahon, 1996
 
3,249
 
10 uterine ruptures (0.3%)
 
Shipp, 1999
 
2,912
 
28 uterine ruptures (1%)
 
Landon, 2004
 
17,898
 
124 uterine ruptures (0.7 %)
 
Macones, 2005 13,331 128 uterine ruptures (0.9%)


*Includes unknown

Unknown hysterotomy

When an obstetrician cannot obtain an operative report of a patient's prior cesarean delivery, obstetric history may be helpful in determining the type of uterine incision. For example, a patient who underwent a cesarean delivery for a breech presentation at 28 weeks' gestation has a much higher risk of a vertical uterine incision than the patient at term with arrest of dilation. Because most cesarean deliveries are via low transverse hysterotomies, the risk of uterine rupture for patients with an unknown uterine scar is usually similar to that of patients who have had a prior transverse incision. Several studies examining this issue have demonstrated that the rate of rupture for patients with an unknown uterine incision is approximately 0.6%. A case-control study of patients with and without uterine rupture did not find unknown hysterotomy to be a risk factor compared with low transverse hysterotomy.5

Number of prior cesarean deliveries

Patients with more than 1 prior cesarean delivery are at increased risk of uterine rupture. The unadjusted rate of uterine rupture for patients with 2 prior uterine incisions ranges from 1.8-3.7%. A recent analysis demonstrated that when potential confounding variables (eg, prior vaginal delivery) are controlled for, patients who have had 2 prior cesarean deliveries have 5 times the risk of uterine rupture compared with patients who have had only 1 prior cesarean delivery (aOR, 4.8). This finding contradicted several earlier studies that did not control for confounding factors, most importantly prior vaginal delivery. More recently, a study that examined major complications overall found that while there was a statistically significant increase, the aOR was only 1.6.

Single-layer uterine closure

While traditionally the uterine hysterotomy had been closed in several layers, in the 1990s, physicians at many institutions began closing the Kerr hysterotomy in a single layer. Because the lower uterine segment is quite thin, a single layer often afforded adequate hemostasis. Several recent studies have compared women whose hysterotomy was closed in a single layer with those whose hysterotomy was closed in 2 layers. Adjusted odds ratios of 3 to 4 for uterine rupture has been estimated for those women who only have a single-layer closure.

Prior vaginal delivery

Prior vaginal delivery appears to be protective for subsequent uterine rupture. A 2000 study by Zelop et al demonstrated that patients with a prior vaginal delivery had a 0.2% rate of rupture compared with 1.1% for patients with no prior vaginal delivery. An adjusted odds ratio controlling for confounding factors was 6.2.6 No studies have compared the rate of uterine rupture in patients with a prior VBAC with those with a vaginal delivery before their prior cesarean delivery. These findings have been validated in subsequent studies, though the effect size has not been quite as large.

Prior infection

A recent study demonstrated that women who had an infection at the time of the cesarean delivery have an increased rate of uterine rupture in a subsequent trial of labor. The assumed causal mechanism is poor healing of the hysterotomy secondary to the infection.

Labor

While labor appears to be a risk factor for uterine rupture, many patients experience a uterine rupture prior to the onset of labor. In a large study using birth certificate data, one study found that the rate of uterine rupture prior to the onset of labor was 0.5%. Patients at greatest risk are those with prior classical hysterotomies. As a result of this potential risk, these patients are usually scheduled for delivery at 36-37 weeks' gestation. When counseling this group of patients, however, mentioning that scheduling an early repeat cesarean delivery does not eliminate the risk of uterine rupture entirely is important.

Induction of labor

Induction of labor as a risk factor for uterine rupture has been examined over only the past 5 years. One large study, which did not control for confounding factors, demonstrated a uterine rupture rate of 2.3% in patients who had experienced induced labor. In several studies controlling for confounding factors, adjusted odds ratios were 2-4 for patients who were induced compared with those who presented in spontaneous labor. Despite these analyses, discerning whether induction of labor itself leads to uterine rupture or whether another risk factor (as yet unmeasured) is associated with both induction of labor and uterine rupture is difficult. When patients have an indication for induction of labor, the best course of management is to discuss the increase over their baseline risk of uterine rupture.

Use of oxytocin

In the only prospective randomized trial in women with a prior cesarean delivery, one study examined the use of oxytocin augmentation in early labor compared with expectant management. In this study, 5 uterine ruptures occurred in the augmentation group (5%) and none occurred in the expectant management group. Excessive use of oxytocin has been described as leading to an increased risk of uterine rupture. A 1993 study by Leung et al demonstrated an odds ratio of 2.7 for uterine rupture in patients who used oxytocin compared with those without oxytocin augmentation.5 However, this study included inductions and augmentation in both the latent and active phases. These confounding factors may have contributed to much of the difference because induction of labor alone has an increased risk.

In more recent studies, oxytocin augmentation was associated with uterine rupture.7 ,8 While the odds ratio was 2.3, it was not statistically significant in the former study (95% CI, 0.8-7.1); this is likely secondary to inadequate power. In the latter study, a similar odds ratio of 2.4 (95% CI, 1.5-3.9) existed. Because labor and delivery units use oxytocin widely, this oxytocin uterine rupture relationship deserves careful consideration; the relationship directly impacts management of patients. At this point, using oxytocin for induction and augmentation is probably advisable only when absolutely necessary.

Use of prostaglandins

Evidence regarding the use of prostaglandins for induction of labor remains scant. However, in the few trials that have been conducted, the trend is toward an increase in the rate of uterine rupture. In 1999, the use of prostaglandin E2 was demonstrated to have an adjusted odds ratio of 3.2 (95% CI, 0.9-10.9). This study controlled for induction of labor, which appears to be an independent risk factor. In 2001, Lydon-Rochelle et al demonstrated a 3-fold increase in the risk for uterine rupture when comparing patients induced with prostaglandins with those induced with oxytocin.9 In the 2004 study by Landon et al, this effect of prostaglandin induction versus other means was smaller—less than 2-fold (OR 3.95 with prostaglandin, 2.48 without prostaglandin).8

As in studies examining the risk of uterine rupture in patients undergoing induction of labor, patients who were treated with prostaglandins were likely to have other confounding variables that were not controlled. In particular, the prostaglandin misoprostol has been examined in small studies. In 1998, Wing et al reported a case series of 17 patients who were induced with misoprostol, in which 2 uterine ruptures occurred. These findings have led to the decreased use of prostaglandins for induction, particularly misoprostol.10

Foley bulb

Only one small study exists of patients with a prior cesarean being induced with the transcervical Foley bulb. In that study, the rate of uterine rupture was 1.1% with spontaneous labor, 1.2% with induction with amniotomy, and 1.6% with use of a transcervical Foley bulb. While this rate is lower than some of the reported rates with prostaglandins, whether the increase seen in patients requiring cervical ripening is due to the need for cervical ripening or the agents themselves is unclear.

Interpregnancy interval

Several studies have demonstrated that the shorter the amount of time between the cesarean delivery and the subsequent delivery, the higher the rate of uterine rupture. Commonly, thresholds of 18 and 24 months have been examined. Adjusted odds ratios range from 2.5-3 for an increased rate of uterine rupture in the women with less time between deliveries. The biologic plausibility here is related to the amount of time required for the uterine scar to heal completely.

Twin gestations

A recent study by Cahill et al revealed that while women with twin gestations are less likely to undergo a trial of labor after prior cesarean, they appear to be at no increased risk for uterine rupture.11 Other smaller studies examined the rate of uterine rupture in patients with twin gestation undergoing a trial of labor after cesarean delivery, and none of these studies demonstrated a frank rupture, although combining their data revealed 5 asymptomatic dehiscences in 151 patients.12 ,13 ,14 The rate of asymptomatic uterine dehiscence in patients undergoing a trial of labor after cesarean delivery is difficult to assess because it is not commonly investigated. Thus, while the overall power examining this issue in twins is not overwhelming, certainly no evidence suggests a higher risk of uterine rupture in these women.

Müllerian anomalies

In 1999, one small series by Ravasia et al examined patients with müllerian anomalies undergoing a trial of labor after cesarean delivery. In this series, 2 uterine ruptures occurred among 25 patients (8%). However, both patients with uterine rupture had undergone induction with prostaglandins; therefore, making any assessment about the relative risk of uterine rupture in this group of patients is difficult. The sample size in this study was certainly too small to consider particular types of uterine anomalies.15

Maternal and neonatal outcomes

When counseling regarding the tradeoffs between a trial of labor and an elective repeat cesarean delivery, several factors should be weighed. As discussed above, the rate of success is important as it has been demonstrated that maternal outcomes are better with a successful trial of labor than elective repeat cesarean delivery but worse with a cesarean delivery after a failed trial of labor. A 2004 study by Landon et al found that the overall measure of morbidity was higher among women who underwent a trial of labor. However, among the 15,801 women who elected to have a repeat cesarean delivery, 2 maternal deaths were reported. Among the 17,898 women who underwent a trial of labor, no maternal deaths were reported due to the trial of labor or uterine rupture. This difference was too small to be statistically significant; however, the risk of repeat cesarean delivery to maternal morbidity and mortality should be considered.8

The other important factor to consider is the neonatal outcomes in the setting of a trial of labor or a uterine rupture. In a large population-based study from Scotland, the authors found that among patients who underwent trial of labor after cesarean delivery, of 15,515 cases, 7 perinatal deaths occurred due to uterine rupture for a rate of 4.5 per 10,000 women. This was compared with no perinatal deaths due to uterine rupture among women undergoing elective repeat cesarean delivery and a rate of 0.5 per 10,000 among women laboring with no prior cesarean delivery. More recently, a study demonstrated that of 15,338 patients at term undergoing a trial of labor, 2 neonatal deaths and 7 cases of hypoxic-ischemic encephalopathy occurred for rates of 1.4 per 10,000 and 4.6 per 10,000 trials of labor, respectively.8 In their series, 114 uterine ruptures occurred among these patients, giving rates of 1.8% of neonatal death per uterine rupture and 6.2% of hypoxic-ischemic encephalopathy peruterinerupture.

Finally, one important individual characteristic that may tip the scales for many women making the decision about whether to undergo a trial of labor is whether they wish to have future pregnancies beyond the current one. As discussed above, once a vaginal birth has been achieved, the chances of future success and the risks of uterine rupture both improve. Further, with each subsequent cesarean delivery, the risks of maternal morbidity and, potentially, maternal mortality increase. Thus, for a woman who wants more children, taking the risk of a trial of labor in the current pregnancy may hold more long-term benefits than the woman who is planning on a tubal ligation after delivery.

Management of Patients With Prior Cesarean Deliveries

Patients with prior cesarean deliveries require special management, both antenatally and in labor and delivery. Early in their prenatal care, catalog patients' preexisting risk factors for both successful VBAC and uterine rupture. If uncertain about the prior hysterotomy facts, obtain the operative notes from patients' cesarean delivery. When all obstetric history is obtained, counsel patients regarding the risks and benefits of undergoing a trial of labor after cesarean delivery, and plan the particular mode of delivery with patients. Again, some providers and hospitals have particular consent forms that must be signed at this point regarding a trial of labor after cesarean delivery.

Once the patient presents to the labor and delivery unit and is in labor, going through the risks and benefits again of a trial of labor after cesarean delivery is advisable. Because of possible changes in the patient's status, these risks may have changed from the prenatal setting. For example, if she presents in active labor, it seems that both her chances of failed VBAC and risk of uterine rupture decrease. In contrast, if she is presenting for induction of labor, her chances of failed VBAC and uterine rupture both increase.

Regarding management on labor and delivery, several practices can help minimize the maternal and neonatal risk. Per ACOG guidelines, have an obstetrician, anesthesiologist, and operating room team immediately available to provide an emergent delivery. Clinically, observe the patient closely for signs of uterine rupture. Harbingers of uterine rupture include the following:

  • Acute abdominal pain, persistent beyond contractions
  • A popping sensation
  • Palpation of fetal parts outside the uterus upon Leopold maneuvers
  • Repetitive or prolonged fetal heart rate deceleration
  • High presenting part upon vaginal examination
  • Vaginal bleeding

Treat any of these findings as a possible uterine rupture until another source for the finding has been identified. Rupture requires immediate delivery.

Summary

Despite the risks (0.5-1% rate of uterine rupture), a trial of labor after cesarean delivery remains an attractive option for many patients and leads to a successful outcome in a high proportion of cases. In comparison, the alternative of elective repeat cesarean delivery is not without risks. In addition to the inherent risks that cesarean delivery has over vaginal delivery, patients may experience uterine rupture prior to the onset of labor.

Certainly, as mentioned above, one component of counseling should include whether patients are interested in subsequent pregnancies after the current pregnancy. As noted above, 2 prior cesarean deliveries further increase the risks of VBAC in a subsequent pregnancy, so for the future pregnancy, having had a successful VBAC offers protection after undergoing the risk in the current pregnancy.

The decision to undergo a trial of labor after cesarean delivery is an individual one that should be based on careful, thorough counseling. Maternal characteristics and obstetric history can provide a patient a rough estimate of her chance of a successful trial of labor. This same obstetric history can be used to estimate a patient's risk of uterine rupture. If possible, avoid induction of labor because induction of labor decreases the probability of success and increases the chance of uterine rupture in a trial of labor after cesarean delivery. Counsel patients who elect to undergo a trial of labor after cesarean delivery to be evaluated early in labor and to manage the pregnancy in a hospital setting in which uterine rupture can be both recognized and managed expediently.

Keywords

vaginal birth after cesarean delivery, VBAC, VBAC delivery, trial of labor after cesarean delivery, prior cesarean delivery, risks for uterine rupture, vaginal delivery, cesarean birth, abdominal delivery, cesarean section, caesarean delivery, caesarean section, C-section, C section, pregnancy complications, difficult pregnancy, trial of labor, hysterotomy, breech presentation, gestational diabetes, pregestational diabetes, induced labor, placenta previa, dystocia, cephalopelvic disproportion, CPD

References

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Wed, 21 Jul 2010 @15:31

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