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Does a higher dosage of oxytocin raise the risk of rupture in VBAC candidates?
EXPERT COMMENTARY
Numerous studies support the safety of a trial of labor after one low-transverse cesarean as an alternative to elective repeat cesarean delivery, with favorable maternal and perinatal outcomes expected for the vast majority of carefully selected patients. Although ACOG acknowledges that oxytocin appears to be relatively safe in patients attempting VBAC, some studies have shown an increased rate of uterine rupture with labor induction and augmentation than with spontaneous labor, suggesting that use of oxytocin may be a risk factor for rupture.1
A focus on maximum dosages
This retrospective study is one of several derived from a large cohort of women with at least one previous low-transverse cesarean delivery performed at one of 17 centers in the United States. Earlier studies from this cohort found that oxytocin alone was not associated with uterine rupture and that no single factor was sufficient to predict rupture.2,3 The majorobjective of this subanalysis was to determine whether higher maximum dosages of oxytocin increase the rate of rupture.
Findings are probably not useful
Despite the strengths of this large study, with observations adjusted for significant confounders, it is limited by its retrospective design, potential bias introduced by nonrandomization, and use of maximum dosage of oxytocin as the primary variable. Many factors are weighed by practitioners when they consider a patient for VBAC and for oxytocin administration, and not all of them could be accounted for in this study: Timing of oxytocin administration, dosing intervals, duration of oxytocin exposure, and total cumulative dosage of oxytocin were not assessed.
Maximum oxytocin dosage was only a fair predictor of uterine rupture, and the authors acknowledge that the maximum dosage of oxytocin is not sufficiently predictive to be clinically useful. Maximum oxytocin dosage is likely only one of the variables affecting the rate of rupture.
Counsel women about greater risk
Although this study contributes to our understanding of uterine rupture in VBAC, its findings do not warrant a change in current clinical practice. The absolute increase of uterine rupture with higher maximum oxytocin dosages was about 1%. Patients should be informed about the possible increased risk of rupture with higher dosages of oxytocin. However, ACOG’s existing recommendations on VBAC should still guide practitioners, and oxytocin should remain an option for properly selected patients in adequately staffed and monitored hospitals.1
Reference
1. American College of Obstetricians and Gynecologists. Vaginal birth after previous cesarean delivery. Practice Bulletin#54. Washington, DC: ACOG; July 2004.
2. Macones GA, Peipert J, Nelson DB, et al. Maternal complications with vaginal birth after cesarean delivery:a multicenter study. C Am J Obstet Gynecol. 2005;193:1656-1662.
3. Macones GA, Cahill AG, Stamilio DM, Odibo A, Peipert J, Stevens EJ. Can uterine rupture in patients attempting vaginal birth after cesarean delivery be predicted? Am J Obstet Gynecol. 2006;195:1148-1152.
EXPERT COMMENTARY
Numerous studies support the safety of a trial of labor after one low-transverse cesarean as an alternative to elective repeat cesarean delivery, with favorable maternal and perinatal outcomes expected for the vast majority of carefully selected patients. Although ACOG acknowledges that oxytocin appears to be relatively safe in patients attempting VBAC, some studies have shown an increased rate of uterine rupture with labor induction and augmentation than with spontaneous labor, suggesting that use of oxytocin may be a risk factor for rupture.1
A focus on maximum dosages
This retrospective study is one of several derived from a large cohort of women with at least one previous low-transverse cesarean delivery performed at one of 17 centers in the United States. Earlier studies from this cohort found that oxytocin alone was not associated with uterine rupture and that no single factor was sufficient to predict rupture.2,3 The majorobjective of this subanalysis was to determine whether higher maximum dosages of oxytocin increase the rate of rupture.
Findings are probably not useful
Despite the strengths of this large study, with observations adjusted for significant confounders, it is limited by its retrospective design, potential bias introduced by nonrandomization, and use of maximum dosage of oxytocin as the primary variable. Many factors are weighed by practitioners when they consider a patient for VBAC and for oxytocin administration, and not all of them could be accounted for in this study: Timing of oxytocin administration, dosing intervals, duration of oxytocin exposure, and total cumulative dosage of oxytocin were not assessed.
Maximum oxytocin dosage was only a fair predictor of uterine rupture, and the authors acknowledge that the maximum dosage of oxytocin is not sufficiently predictive to be clinically useful. Maximum oxytocin dosage is likely only one of the variables affecting the rate of rupture.
Counsel women about greater risk
Although this study contributes to our understanding of uterine rupture in VBAC, its findings do not warrant a change in current clinical practice. The absolute increase of uterine rupture with higher maximum oxytocin dosages was about 1%. Patients should be informed about the possible increased risk of rupture with higher dosages of oxytocin. However, ACOG’s existing recommendations on VBAC should still guide practitioners, and oxytocin should remain an option for properly selected patients in adequately staffed and monitored hospitals.1
EXPERT COMMENTARY
Numerous studies support the safety of a trial of labor after one low-transverse cesarean as an alternative to elective repeat cesarean delivery, with favorable maternal and perinatal outcomes expected for the vast majority of carefully selected patients. Although ACOG acknowledges that oxytocin appears to be relatively safe in patients attempting VBAC, some studies have shown an increased rate of uterine rupture with labor induction and augmentation than with spontaneous labor, suggesting that use of oxytocin may be a risk factor for rupture.1
A focus on maximum dosages
This retrospective study is one of several derived from a large cohort of women with at least one previous low-transverse cesarean delivery performed at one of 17 centers in the United States. Earlier studies from this cohort found that oxytocin alone was not associated with uterine rupture and that no single factor was sufficient to predict rupture.2,3 The majorobjective of this subanalysis was to determine whether higher maximum dosages of oxytocin increase the rate of rupture.
Findings are probably not useful
Despite the strengths of this large study, with observations adjusted for significant confounders, it is limited by its retrospective design, potential bias introduced by nonrandomization, and use of maximum dosage of oxytocin as the primary variable. Many factors are weighed by practitioners when they consider a patient for VBAC and for oxytocin administration, and not all of them could be accounted for in this study: Timing of oxytocin administration, dosing intervals, duration of oxytocin exposure, and total cumulative dosage of oxytocin were not assessed.
Maximum oxytocin dosage was only a fair predictor of uterine rupture, and the authors acknowledge that the maximum dosage of oxytocin is not sufficiently predictive to be clinically useful. Maximum oxytocin dosage is likely only one of the variables affecting the rate of rupture.
Counsel women about greater risk
Although this study contributes to our understanding of uterine rupture in VBAC, its findings do not warrant a change in current clinical practice. The absolute increase of uterine rupture with higher maximum oxytocin dosages was about 1%. Patients should be informed about the possible increased risk of rupture with higher dosages of oxytocin. However, ACOG’s existing recommendations on VBAC should still guide practitioners, and oxytocin should remain an option for properly selected patients in adequately staffed and monitored hospitals.1
Reference
1. American College of Obstetricians and Gynecologists. Vaginal birth after previous cesarean delivery. Practice Bulletin#54. Washington, DC: ACOG; July 2004.
2. Macones GA, Peipert J, Nelson DB, et al. Maternal complications with vaginal birth after cesarean delivery:a multicenter study. C Am J Obstet Gynecol. 2005;193:1656-1662.
3. Macones GA, Cahill AG, Stamilio DM, Odibo A, Peipert J, Stevens EJ. Can uterine rupture in patients attempting vaginal birth after cesarean delivery be predicted? Am J Obstet Gynecol. 2006;195:1148-1152.
Reference
1. American College of Obstetricians and Gynecologists. Vaginal birth after previous cesarean delivery. Practice Bulletin#54. Washington, DC: ACOG; July 2004.
2. Macones GA, Peipert J, Nelson DB, et al. Maternal complications with vaginal birth after cesarean delivery:a multicenter study. C Am J Obstet Gynecol. 2005;193:1656-1662.
3. Macones GA, Cahill AG, Stamilio DM, Odibo A, Peipert J, Stevens EJ. Can uterine rupture in patients attempting vaginal birth after cesarean delivery be predicted? Am J Obstet Gynecol. 2006;195:1148-1152.
VBAC: When is it safe?
- Selection criteria useful for identifying candidates for VBAC include: a limit of 1 prior low-transverse cesarean, clinically adequate pelvis, no other uterine scars or previous rupture, and no contraindications.
- Offer VBAC only if obstetric care and anesthesiology are available throughout active labor, in case emergency cesarean is necessary.
- Single-layer uterine closure may increase the risk of rupture during subsequent labors.
- Epidural anesthesia is safe for women undergoing a trial of labor.
The new bulletin reaffirms the previous recommendation that obstetric and anesthesia personnel be immediately available throughout active labor, in case emergency cesarean is necessary.
VBAC is still within the standard of care, but rates were declining even before the new bulletin was released: from a high of 28.3% in 1996 to 12.6% in 2002.2
Benefits of VBAC may outweigh the risks in most women with 1 previous low-transverse cesarean,3 but even with optimal facilities and personnel, numerous factors warrant special caution, according to recent studies I’ll review in this article.
Recent studies of risks and benefits
No randomized trials. ACOG notes,1 “Despite thousands of citations in the world’s literature, there are currently no randomized trials comparing maternal or neonatal outcomes for both repeat cesarean delivery and VBAC.”
Success rates are similar for gravidas with previous cesarean for a nonrecurring indication and those with no previous cesarean.4-6
Uterine rupture is more likely during a trial of labor, but the rate is usually below 1%.7-9
Other limiting factors may include labor augmentation and induction, maternal obesity, gestational age beyond 40 weeks, birth weight over 4,000 g, and an interdelivery interval of less than 19 months.10-17
When a trial of labor fails, women face a heightened risk of uterine rupture, hysterectomy, transfusion, and endometritis.3,4,9
Perinatal death is more likely during VBAC than planned repeat cesarean, although the death rate is usually less than 1%.3,8,9,18
Indications and contraindications
The TABLE outlines potential candidates, ineligible gravidas, resources needed, and situations that warrant caution.
Don’t assume: Check the previous operative note
It is all too easy to presume that a previous cesarean section at term was performed through a transverse incision in the lower uterine segment.
While this may be true in the majority of cases, the actual operative note may reveal information relevant to the delivery decision: an extensive tear of the uterine incision, previously unrecognized uterine anomalies, or the need to perform a classical or T-shaped incision to facilitate delivery of the infant.
For these reasons, review the actual operative report whenever possible before a trial of labor.
2 prior low-transverse incisions
While this is not an absolute contraindication to VBAC, in today’s cautious climate ACOG recommends VBAC proceed only when there is also a history of successful vaginal delivery.1,19 Otherwise, women with 2 or more previous cesareans should undergo repeat abdominal birth.
Prior low-vertical incision
Although successful VBACs have been reported in women with a prior low-vertical uterine incision, many experts feel that these incisions often extend superiorly into the upper uterus and thus increase the likelihood of uterine rupture in subsequent labors.20,21
Greater risk with single-layer closure
Single-layer uterine closure appears to increase the likelihood of rupture during subsequent labors.22 As a result, many physicians have returned to 2-layer closure of the lower transverse uterine incision. It is unclear whether single-layer closure is a contraindication to subsequent labor, but it does warrant caution due to a 4-fold increase in the risk of rupture.22
Discourage closely spaced gestations
The shorter the interval between deliveries, the more likely is uterine rupture during a trial of labor.23,24 For those considering a subsequent VBAC, I recommend trying to space their next delivery at least 18 months after cesarean birth.
Labor induction increases risk
Spontaneous labor leads to successful VBAC more often than does labor induction or augmentation. In addition, a recent study found 5 times the risk of uterine rupture when oxytocin was used to induce labor, compared with elective repeat cesarean—although the rate of rupture was less than 1% in both groups.25
The use of prostaglandins in labor induction greatly increases the risk of rupture, with rates of 24.5 per 1,000 reported, compared with 5.2 per 1,000 in women with spontaneous labor.26 ACOG strongly discourages the use of prostaglandin cervical ripening agents in labor inductions.26
Seek out other factors
Women who initially appear eligible may harbor other characteristics or conditions that warrant special attention.15,26-28
External cephalic version. Although 1 study29 concluded it is effective in women undergoing a trial of labor after cesarean, vigilance is recommended.
Twin gestations. Two retrospective studies involving a total of 45 women found VBAC to be safe in twin gestations. Because of the limited number of women studied and the lack of randomized, controlled trials, caution is strongly advised.30,31
Macrosomia. The rate of uterine rupture rises in women who have not had a previous vaginal delivery.27
Postdates. Although VBAC is less likely to succeed after 40 weeks’ gestation, the risk of uterine rupture increases only with induction of labor.11
Analgesia. Women undergoing a trial of labor can receive epidural anesthesia without increasing the risk of rupture or failed VBAC and without obscuring the signs and symptoms of uterine rupture.32,33 In fact, as ACOG notes, effective pain relief may encourage more women to try VBAC.1
Previous vaginal delivery. Women who have delivered vaginally are more likely to succeed at VBAC—by a factor of 9 to 28—than those who have not.34,35
Other conditions such as maternal obesity and advanced age should be evaluated in light of the patient’s overall risk-benefit profile. Although caution is recommended, definitive data are lacking.
TABLE
Criteria for trial of labor
| QUALIFICATIONS |
| 1 prior low-transverse cesarean section |
| Clinically adequate pelvis |
| No other uterine scars |
| DISQUALIFICATIONS |
| Prior classical or T-shaped uterine incision |
| Multiple uterine incisions |
| Previous uterine rupture |
| Contracted pelvis |
| Contraindications to vaginal birth |
| REQUIREMENTS THROUGHOUT ACTIVE LABOR |
| Obstetrician immediately available |
| Continuous electronic monitoring of the fetal heart rate |
| Personnel skilled in interpreting fetal tracings |
| Anesthesia for emergency cesarean |
| Physician qualified for emergency cesarean |
| PRECAUTIONS |
| Unknown uterine scars |
| Prior low vertical uterine incision |
| Uterine malformations |
| Prior single-layer uterine closure |
| Short interdelivery interval |
| Need for labor induction |
| Need for external cephalic version |
| Twin gestation |
| Suspected macrosomia |
| Maternal obesity |
| Postdates |
| Advanced maternal age |
| No prior vaginal delivery |
| Source: ACOG1 |
Prognostic formulas
One decision analysis36 concluded that VBAC is a reasonable option when the chance of success exceeds 50% and the desire for future pregnancy is 10% to 20% or more. Although scoring systems have been proposed to predict the likelihood of success, individualized assessment of each patient is ideal. (See “Case by case: Adding up the decisive factors”.)
CASE 1
A single cesarean and a healthy fetus
After her obstetrician encourages a repeat cesarean at 39 weeks’ gestation, a 39-year-old gravida seeks a second opinion. Her obstetric history includes a remote first-trimester miscarriage and a cesarean section, 2 years prior, of vertex-vertex twins at 36 weeks for arrest of labor at 8 cm. Tubal ligation is planned after delivery.
The previous operative report indicates that a low-transverse uterine incision was repaired in 2 layers. The patient plans to deliver at a local community hospital without full-time, in-hospital anesthesiology services.
This pregnancy has been uncomplicated, and ultrasound has confirmed a normally grown fetus in vertex presentation with a fundal placenta. The patient is considering vaginal birth after cesarean (VBAC).
Decision Multiple factors make VBAC unwise
This patient is a poor candidate due to advanced maternal age, no prior vaginal birth, and the previous cesarean for failure to progress. Lack of round-the-clock anesthesiology at her chosen hospital contraindicates trial of labor.1
Her request for postpartum sterilization also makes repeat cesarean wiser.
After these risks are explained, the patient accepts the recommendation for elective repeat cesarean.
CASE 2
Breech presentation, short interdelivery interval
A 28-year-old gravida has a breech presentation at 37 weeks. She has had 3 spontaneous vaginal deliveries and 1 cesarean section at term for a nonreassuring fetal tracing in labor. The cesarean was 14 months ago. The operative note is not available. She says she was told future vaginal deliveries would be possible.
She plans to have a large family.
Apart from the breech presentation, this pregnancy has been uneventful. The patient requests external cephalic version prior to a trial of labor.
Decision Take future plans into account
Placenta previa, accreta, adhesions, and intraoperative injuries are recognized risks in patients with a higher number of cesarean deliveries.
In this case, breech presentation, a short interdelivery interval, and an undocumented uterine incision warrant caution. Given that the patient’s cesarean section was performed at term in the United States, and that she was told she would be able to have a subsequent vaginal birth, she underwent a successful external cephalic version in the delivery room. She had an uneventful spontaneous vaginal delivery 3 weeks later.
CASE 3
Good candidate, nervous about risk
A 30-year-old woman with 1 uncomplicated vaginal delivery and 1 cesarean section 3 years prior presents in her third pregnancy for counseling about VBAC.
Her cesarean was performed through a transverse incision in the lower uterine segment for repetitive deep variable decelerations. A friend recently experienced uterine rupture during a trial of labor, resulting in a hysterectomy. She is undecided about future childbearing.
Decision Patient and physician agree on cesarean
With a prior vaginal delivery and a previous cesarean through a low-transverse uterine incision over 18 months ago for an indication that is unlikely to recur, the likelihood of VBAC success is high.
However, the patient was worried by potential risks for uterine rupture, adverse perinatal outcome, and loss of future reproductive potential. After considering the risks and benefits, she requested a repeat cesarean delivery.
After fully counseling the patient on the risks and benefits of VBAC versus elective repeat cesarean, a management plan was made and documented.
The patient underwent an uncomplicated cesarean section at 39 weeks and delivered a healthy baby.
VBAC is not an option where facilities fall short
Despite meeting VBAC criteria for previous incision or pelvic adequacy, many US women do not have the option of a trial of labor. The reason: the need for obstetric care providers throughout active labor and the ability to perform an emergency cesarean.1 As a result, many midwives and family practitioners can no longer care for VBAC patients independently.
Continuous monitoring is a must
It is the potential for uterine rupture that places patients at risk for unfavorable obstetric outcomes—and rupture can be hard to predict. A nonreassuring fetal heart rate is the most frequent sign.1 Others are uterine or abdominal pain, vaginal bleeding, loss of station of the presenting part, and hypovolemia.1
Continuous electronic monitoring of the fetal heart has the potential to detect nonreassuring events earlier than intermittent auscultation. Thus, continuous fetal heart rate monitoring has become the standard for women attempting VBAC. When it is unavailable, VBAC should not be offered.
Also crucial: Anesthesiology
ACOG recommends that anesthesia and other personnel be on hand in case emergency cesarean is warranted.1 While teaching hospitals and large referral centers are constantly staffed with obstetricians and anesthesiologists, birthing centers and smaller community-based hospitals often lack such coverage. As a result, some physicians and hospitals have withdrawn VBAC as an option
Reducing medicolegal risk
When a trial of labor results in uterine rupture or other adverse outcomes, the patient is more likely to sue. Informed consent and thorough documentation of the VBAC decision are crucial and should include37:
- Appropriate discussion of maternal and perinatal risks and benefits, and documentation of this exchange.
- A clear statement of the woman’s intention to undergo a trial of labor after cesarean delivery.
- If possible, documentation of previous uterine scar on the prenatal record.
- Appropriate counseling about the increased risk of rupture when labor is induced with oxytocin, and documentation of this discussion.
- Counseling about the increased risk of rupture when a trial of labor follows a previous cesarean by less than 19 months.
- Discussion about decreased likelihood of success if the woman is obese, is of advanced age, or has not had a prior vaginal birth.
Is VBAC availability better for health and happiness?
Many women want the option of a trial of labor after cesarean because it affords them the opportunity to experience vaginal delivery. Women who have undergone both cesarean and vaginal deliveries usually opt for a trial of labor in their next pregnancy.38 When a physician or hospital eliminates VBAC as an option, it can lead to patient dissatisfaction—as well as loss of revenue if a woman seeks care elsewhere.
Risk of placenta accreta
If elective repeat cesarean were the only option, the incidence of placenta accreta would increase over time.
Placenta accreta is strongly linked to placenta previa, a condition recognized to increase as the number of previous cesarean sections rises.39,40 A woman with 2 prior cesareans has a 2% incidence of placenta previa; nearly half of these cases are associated with placenta accreta.41 As a result, complications of accreta such as maternal death, need for substantial transfusion, postoperative infection, and intraoperative urinary tract injuries would be expected to increase if VBAC were abandoned.42
For this reason, it is important to ask about the patient’s childbearing goals. If a large family is planned, the potential risk of placenta accreta should be explained.
Assess for accreta. All patients with a prior cesarean section require careful evaluation of placental location and assessment for possible accreta should placenta previa or a low-lying placenta be identified prenatally.
I have found both ultrasound and magnetic resonance imaging useful in recognizing accreta, allowing for adequate preoperative preparation and more favorable outcomes. If accreta is not detected until the time of elective repeat cesarean, it can be life-threatening for the patient.
Should we abandon VBAC?
An unfortunate result of the initiatives promoting VBAC in the 1980s and 90s was a higher rate of uterine rupture, since many women with previous cesarean were strongly encouraged—even required—to undergo a trial of labor. Now that elective repeat cesareans are again on the rise, the risk of rupture should diminish due to better VBAC patient selection, but will probably remain substantially higher than for repeat cesarean.
What exactly is the risk of rupture?
In 1 population-based, retrospective cohort analysis25 involving 20,095 women with 1 previous cesarean section, researchers found a rate of uterine rupture of 5.2 per 1,000 women when labor was spontaneous, compared with 1.6 per 1,000 women who underwent elective repeat cesarean without labor. For women having labor induced with prostaglandins or by other means, the rates were 24.5 and 7.7 per 1,000, respectively.
In the same study, the relative risk of uterine rupture was 3.3 for women presenting in spontaneous labor, compared with those who underwent repeat cesarean without labor; it was 15.6 and 4.9 for women whose labor was induced with prostaglandins or by other means, respectively. The rate of infant mortality was 5.5% in cases involving uterine rupture, compared with 0.5% without rupture.25
Note that this study covered the years 1987 through 1996—and thus predated ACOG rules requiring round-the-clock obstetric and anesthesia care, and those barring prostaglandins for labor induction.
Perinatal death more likely with VBAC, but absolute risk is low
A separate population-based, retrospective, cohort study18 focused on different outcomes: intrapartum stillbirth or neonatal death. This study involved 313,238 singleton births at 37 to 43 weeks’ gestation with the fetus in a cephalic presentation.
Among the women opting for VBAC, the overall rate of delivery-related perinatal death was 12.9 per 10,000 women. This was approximately 11 times greater than the risk associated with planned repeat cesarean, more than twice the risk associated with labor in multiparous women, and similar to the risk among nulliparous women in labor. However, in absolute terms, the risk of perinatal death associated with a trial of labor and uterine rupture was low: 1 in 2,200.18
What’s the bottom line?
Are findings such as these reason to abandon VBAC? Not necessarily. VBAC success rates range from 60% to 80%, and a 1991 meta-analysis43 of more than 30 US studies found lower maternal febrile morbidity after a trial of labor than after repeat cesarean, and no differences between the 2 approaches in uterine dehiscence, rupture, or perinatal mortality.
A more recent meta-analysis9 of international studies involving 47,682 women found a uterine rupture rate of 0.4% for women undergoing a trial of labor versus 0.2% for those having elective repeat cesarean. A later meta-analysis, also international, found an overall uterine rupture rate of 6.2 per 1,000 women attempting VBAC, with a perinatal mortality rate of 0.4 per 1,000. Perinatal mortality was significantly lower among US studies.6
Nevertheless, when it comes to VBAC, absolute risks are low, and planned repeat cesarean does not eliminate them entirely. Elective cesarean carries a risk of maternal death up to 2.8 times that of vaginal delivery, though absolute risk is low.44
Thus, when patients are carefully selected and fully informed of benefits and risks, VBAC should remain an available option.
The author reports no relevant financial relationships.
1. American College of Obstetricians and Gynecologists. ACOG Practice Bulletin #54: Vaginal Birth After Previous Cesarean Delivery. Washington, DC: ACOG; July 2004.
2. Martin JA, Hamilton BE, Sutton PD, Ventura SJ, Menacker F, Munson ML. Births: final data for 2002. Natl Vital Stat Rep. 2003;52(10):1-113.
3. Rageth JC, Juzi C, Grossenbacher H. for the Swiss Working Group of Obstetric and Gynecologic Institutions. Delivery after previous cesarean: a risk evaluation. Obstet Gynecol. 1999;93:332-337.
4. Hibbard JU, Ismail MA, Wang Y, Te C, Karrison T, Ismail MA. Failed vaginal birth after a cesarean section: how risky is it? I. Maternal morbidity. Am J Obstet Gynecol. 2001;184:1365-1371;discussion 1371–1373.
5. Bujold E, Gauthier RJ. Should we allow a trial of labor after a previous cesarean for dystocia in the second stage of labor? Obstet Gynecol. 2001;98:652-655.
6. Chauhan SP, Martin JN, Jr, Henrichs CE, Morrison JC, Magann EF. Maternal and perinatal complications with uterine rupture in 142,075 patients who attempted vaginal birth after cesarean delivery: a review of the literature. Am J Obstet Gynecol. 2003;189:408-417.
7. Gregory KD, Korst LM, Cane P, Platt LD, Kahn K. Vaginal birth after cesarean and uterine rupture rates in California. Obstet Gynecol. 1999;94:985-989.
8. Kieser KE, Baskett TF. A 10-year population-based study of uterine rupture. Obstet Gynecol. 2002;100:749-753.
9. Mozurkewich EL, Hutton EK. Elective repeat cesarean delivery versus trial of labor: a meta-analysis of the literature from 1989 to 1999. Am J Obstet Gynecol. 2000;183:1187-1197.
10. Zelop CM, Shipp TD, Repke JT, Cohen A, Lieberman E. Outcomes of a trial of labor following previous cesarean delivery among women with fetuses weighing >4,000 g. Am J Obstet Gynecol. 2001;185:903-905.
11. Zelop CM, Shipp TD, Cohen A, Repke JT, Lieberman E. Trial of labor after 40 weeks’ gestation in women with prior cesarean. Obstet Gynecol. 2001;97:391-393.
12. Macones GA, Hausman N, Edelstein R, Stamilio DM, Marder SJ. Predicting outcomes of trials of labor in women attempting vaginal birth after cesarean delivery: a comparison of multivariate methods with neural networks. Am J Obstet Gynecol. 2001;184:409-413.
13. Ravasia DJ, Wood SL, Pollard JK. Uterine rupture during induced trial of labor among women with previous cesarean delivery. Am J Obstet Gynecol. 2000;183:1176-1179.
14. Sims EJ, Newman RB, Hulsey TC. Vaginal birth after cesarean: to induce or not to induce. Am J Obstet Gynecol. 2001;184:1122-1124.
15. Chauhan SP, Magann EF, Carroll CS, Barrilleaux PS, Scardo JA, Marttin JN, Jr. Mode of delivery for the morbidly obese with prior cesarean delivery: vaginal versus repeat cesarean section. Am J Obstet Gynecol. 2001;185:349-354.
16. Carroll CS, Sr, Magann EF, Chauhan SP, Klauser CK, Morrison JC. Vaginal birth after cesarean section versus elective repeat cesarean delivery: weight-based outcomes. Am J Obstet Gynecol. 2003;188:1516-1520;discussion 1520–1522.
17. Huang WH, Nakashima DK, Rumney PJ, Keegan KA, Jr, Chan K. Interdelivery interval and the success of vaginal birth after cesarean delivery. Obstet Gynecol. 2002;99:41-44.
18. Smith GC, Pell JP, Cameron AD, Dobbie R. Risk of perinatal death associated with labor after previous cesarean delivery in uncomplicated term pregnancies. JAMA. 2002;287:2684-2690.
19. Bretelle F, Cravello L, Shojai R, Roger V, D’Ercole C, Blanc B. Vaginal birth following two previous cesarean sections. Eur J Obstet Gynecol Reprod Biol. 2001;94:23-26.
20. Shipp TD, Zelop CM, Repke JT, Cohen A, Caughey AB, Lieberman E. Intrapartum uterine rupture and dehiscence in patients with prior lower uterine segment vertical and transverse incisions. Obstet Gynecol. 1999;94:735-740.
21. Naef RW, Ray MA, Chauhan SP, Roach H, Blake PG, Martin JN. Trial of labor after cesarean delivery with a lower-segment, vertical uterine incision: is it safe? Am J Obstet Gynecol. 1995;172:1666-1673.
22. Bujold E, Mehta SH, Bujold C, Gauthier RJ. Interdelivery interval and uterine rupture. Am J Obstet Gynecol. 2002;187:1199-1202.
23. Shipp TD, Zelop CM, Repke JT, Cohen A, Lieberman E. Interdelivery interval and risk of symptomatic uterine rupture. Obstet Gynecol. 2001;97:175-177.
24. Esposito MA, Menihan CA, Malee MP. Association of interpregnancy interval with uterine scar failure in labor: a case control study. Am J Obstet Gynecol. 2000;183:1180-1183.
25. Lydon-Rochelle M, Holt VL, Easterling TR, Martin DP. Risk of uterine rupture during labor among women with a prior cesarean delivery. N Engl J Med. 2001;345:3-8.
26. American College of Obstetricians and Gynecologists, Committee on Obstetric Practice. Committee Opinion: Induction of labor for vaginal birth after cesarean delivery. Obstet Gynecol. 2002;99:679-680.
27. Elkousy MA, Sammel M, Stevens E, Peipert JF, Macones G. The effect of birth weight on vaginal birth after cesarean delivery success rates. Am J Obstet Gynecol. 2003;188:824-830.
28. Zelop CM, Shipp TD, Repke JT, Cohen A, Lieberman E. Effects of previous vaginal delivery on the risk of uterine rupture during a subsequent trial of labor. Am J Obstet Gynecol. 2000;183:1184-1186.
29. Flamm BL, Fried MW, Lonky NM, Giles WS. External cephalic version after previous cesarean section. Am J Obstet Gynecol. 1991;165:370-372.
30. Myles T. Vaginal birth of twins after a previous cesarean section. J Matern Fetal Med. 2001;10:171-174.
31. Sansregret A, Bujold E, Gauthier RJ. Twin delivery after a previous cesarean: a 12-year experience. J Obstet Gynaecol Can. 2003;25:294-298.
32. Johnson C, Oriol N. The role of epidural anesthesia in trial of labor. Reg Anesth. 1990;15:304-308.
33. Sakala EP, Kaye S, Murray RD, Munson LJ. Epidural analgesia. Effect on the likelihood of a successful trial of labor after cesarean section. J Reprod Med. 1990;35:886-890.
34. Flamm BL. Once a cesarean, always a controversy. Obstet Gynecol. 1997;90:312-315.
35. McNally OM, Turner MJ. Induction of labor after 1 previous caesarean section. Aust N Z J Obstet Gynaecol. 1999;39:425-429.
36. Mankuta DD, Leshno MM, Menasche MM, Brezis MM. Vaginal birth after cesarean section: trial of labor or repeat cesarean section? A decision analysis. Am J Obstet Gynecol. 2003;189:714-719.
37. Martel MJ, MacKinnon CJ. Clinical Practice Obstetrics Committee of the Society of Obstetricians and Gynaecologists of Canada. Guidelines for vaginal birth after previous Caesarean birth. J Obstet Gynaecol Can. 2004;26:660-683.
38. McMahon MJ, Luther ER, Bowes WA, Olshan AF. Comparison of a trial of labor with an elective second section. N Engl J Med. 1996;335:689-695.
39. Ananth CV, Smulian JC, Vintzileos AM. The association of placenta previa with history of cesarean delivery and abortion: a metaanalysis. Am J Obstet Gynecol. 1997;177:1071-1078.
40. Miller DA, Chollet JA, Goodwin TM. Clinical risk factors for placenta previa-placenta accreta. Am J Obstet Gynecol. 1997;177:210-214.
41. Clark SL, Koonings PP, Phelan JP. Placenta previa/accreta and prior cesarean section. Obstet Gynecol. 1985;66:89-92.
42. O’Brien JM, Barton JR, Donaldson ES. The management of placenta percreta: conservative and operative strategies. Am J Obstet Gynecol. 1996;175:1632-1638.
43. Rosen MG, Dickinson JC, Westhoff CL. Vaginal birth after cesarean: a meta-analysis of morbidity and mortality. Obstet Gynecol. 1991;77:465-470.
44. Hall MH, Bewley S. Maternal mortality and mode of delivery. Lancet. 1999;354:776.-
- Selection criteria useful for identifying candidates for VBAC include: a limit of 1 prior low-transverse cesarean, clinically adequate pelvis, no other uterine scars or previous rupture, and no contraindications.
- Offer VBAC only if obstetric care and anesthesiology are available throughout active labor, in case emergency cesarean is necessary.
- Single-layer uterine closure may increase the risk of rupture during subsequent labors.
- Epidural anesthesia is safe for women undergoing a trial of labor.
The new bulletin reaffirms the previous recommendation that obstetric and anesthesia personnel be immediately available throughout active labor, in case emergency cesarean is necessary.
VBAC is still within the standard of care, but rates were declining even before the new bulletin was released: from a high of 28.3% in 1996 to 12.6% in 2002.2
Benefits of VBAC may outweigh the risks in most women with 1 previous low-transverse cesarean,3 but even with optimal facilities and personnel, numerous factors warrant special caution, according to recent studies I’ll review in this article.
Recent studies of risks and benefits
No randomized trials. ACOG notes,1 “Despite thousands of citations in the world’s literature, there are currently no randomized trials comparing maternal or neonatal outcomes for both repeat cesarean delivery and VBAC.”
Success rates are similar for gravidas with previous cesarean for a nonrecurring indication and those with no previous cesarean.4-6
Uterine rupture is more likely during a trial of labor, but the rate is usually below 1%.7-9
Other limiting factors may include labor augmentation and induction, maternal obesity, gestational age beyond 40 weeks, birth weight over 4,000 g, and an interdelivery interval of less than 19 months.10-17
When a trial of labor fails, women face a heightened risk of uterine rupture, hysterectomy, transfusion, and endometritis.3,4,9
Perinatal death is more likely during VBAC than planned repeat cesarean, although the death rate is usually less than 1%.3,8,9,18
Indications and contraindications
The TABLE outlines potential candidates, ineligible gravidas, resources needed, and situations that warrant caution.
Don’t assume: Check the previous operative note
It is all too easy to presume that a previous cesarean section at term was performed through a transverse incision in the lower uterine segment.
While this may be true in the majority of cases, the actual operative note may reveal information relevant to the delivery decision: an extensive tear of the uterine incision, previously unrecognized uterine anomalies, or the need to perform a classical or T-shaped incision to facilitate delivery of the infant.
For these reasons, review the actual operative report whenever possible before a trial of labor.
2 prior low-transverse incisions
While this is not an absolute contraindication to VBAC, in today’s cautious climate ACOG recommends VBAC proceed only when there is also a history of successful vaginal delivery.1,19 Otherwise, women with 2 or more previous cesareans should undergo repeat abdominal birth.
Prior low-vertical incision
Although successful VBACs have been reported in women with a prior low-vertical uterine incision, many experts feel that these incisions often extend superiorly into the upper uterus and thus increase the likelihood of uterine rupture in subsequent labors.20,21
Greater risk with single-layer closure
Single-layer uterine closure appears to increase the likelihood of rupture during subsequent labors.22 As a result, many physicians have returned to 2-layer closure of the lower transverse uterine incision. It is unclear whether single-layer closure is a contraindication to subsequent labor, but it does warrant caution due to a 4-fold increase in the risk of rupture.22
Discourage closely spaced gestations
The shorter the interval between deliveries, the more likely is uterine rupture during a trial of labor.23,24 For those considering a subsequent VBAC, I recommend trying to space their next delivery at least 18 months after cesarean birth.
Labor induction increases risk
Spontaneous labor leads to successful VBAC more often than does labor induction or augmentation. In addition, a recent study found 5 times the risk of uterine rupture when oxytocin was used to induce labor, compared with elective repeat cesarean—although the rate of rupture was less than 1% in both groups.25
The use of prostaglandins in labor induction greatly increases the risk of rupture, with rates of 24.5 per 1,000 reported, compared with 5.2 per 1,000 in women with spontaneous labor.26 ACOG strongly discourages the use of prostaglandin cervical ripening agents in labor inductions.26
Seek out other factors
Women who initially appear eligible may harbor other characteristics or conditions that warrant special attention.15,26-28
External cephalic version. Although 1 study29 concluded it is effective in women undergoing a trial of labor after cesarean, vigilance is recommended.
Twin gestations. Two retrospective studies involving a total of 45 women found VBAC to be safe in twin gestations. Because of the limited number of women studied and the lack of randomized, controlled trials, caution is strongly advised.30,31
Macrosomia. The rate of uterine rupture rises in women who have not had a previous vaginal delivery.27
Postdates. Although VBAC is less likely to succeed after 40 weeks’ gestation, the risk of uterine rupture increases only with induction of labor.11
Analgesia. Women undergoing a trial of labor can receive epidural anesthesia without increasing the risk of rupture or failed VBAC and without obscuring the signs and symptoms of uterine rupture.32,33 In fact, as ACOG notes, effective pain relief may encourage more women to try VBAC.1
Previous vaginal delivery. Women who have delivered vaginally are more likely to succeed at VBAC—by a factor of 9 to 28—than those who have not.34,35
Other conditions such as maternal obesity and advanced age should be evaluated in light of the patient’s overall risk-benefit profile. Although caution is recommended, definitive data are lacking.
TABLE
Criteria for trial of labor
| QUALIFICATIONS |
| 1 prior low-transverse cesarean section |
| Clinically adequate pelvis |
| No other uterine scars |
| DISQUALIFICATIONS |
| Prior classical or T-shaped uterine incision |
| Multiple uterine incisions |
| Previous uterine rupture |
| Contracted pelvis |
| Contraindications to vaginal birth |
| REQUIREMENTS THROUGHOUT ACTIVE LABOR |
| Obstetrician immediately available |
| Continuous electronic monitoring of the fetal heart rate |
| Personnel skilled in interpreting fetal tracings |
| Anesthesia for emergency cesarean |
| Physician qualified for emergency cesarean |
| PRECAUTIONS |
| Unknown uterine scars |
| Prior low vertical uterine incision |
| Uterine malformations |
| Prior single-layer uterine closure |
| Short interdelivery interval |
| Need for labor induction |
| Need for external cephalic version |
| Twin gestation |
| Suspected macrosomia |
| Maternal obesity |
| Postdates |
| Advanced maternal age |
| No prior vaginal delivery |
| Source: ACOG1 |
Prognostic formulas
One decision analysis36 concluded that VBAC is a reasonable option when the chance of success exceeds 50% and the desire for future pregnancy is 10% to 20% or more. Although scoring systems have been proposed to predict the likelihood of success, individualized assessment of each patient is ideal. (See “Case by case: Adding up the decisive factors”.)
CASE 1
A single cesarean and a healthy fetus
After her obstetrician encourages a repeat cesarean at 39 weeks’ gestation, a 39-year-old gravida seeks a second opinion. Her obstetric history includes a remote first-trimester miscarriage and a cesarean section, 2 years prior, of vertex-vertex twins at 36 weeks for arrest of labor at 8 cm. Tubal ligation is planned after delivery.
The previous operative report indicates that a low-transverse uterine incision was repaired in 2 layers. The patient plans to deliver at a local community hospital without full-time, in-hospital anesthesiology services.
This pregnancy has been uncomplicated, and ultrasound has confirmed a normally grown fetus in vertex presentation with a fundal placenta. The patient is considering vaginal birth after cesarean (VBAC).
Decision Multiple factors make VBAC unwise
This patient is a poor candidate due to advanced maternal age, no prior vaginal birth, and the previous cesarean for failure to progress. Lack of round-the-clock anesthesiology at her chosen hospital contraindicates trial of labor.1
Her request for postpartum sterilization also makes repeat cesarean wiser.
After these risks are explained, the patient accepts the recommendation for elective repeat cesarean.
CASE 2
Breech presentation, short interdelivery interval
A 28-year-old gravida has a breech presentation at 37 weeks. She has had 3 spontaneous vaginal deliveries and 1 cesarean section at term for a nonreassuring fetal tracing in labor. The cesarean was 14 months ago. The operative note is not available. She says she was told future vaginal deliveries would be possible.
She plans to have a large family.
Apart from the breech presentation, this pregnancy has been uneventful. The patient requests external cephalic version prior to a trial of labor.
Decision Take future plans into account
Placenta previa, accreta, adhesions, and intraoperative injuries are recognized risks in patients with a higher number of cesarean deliveries.
In this case, breech presentation, a short interdelivery interval, and an undocumented uterine incision warrant caution. Given that the patient’s cesarean section was performed at term in the United States, and that she was told she would be able to have a subsequent vaginal birth, she underwent a successful external cephalic version in the delivery room. She had an uneventful spontaneous vaginal delivery 3 weeks later.
CASE 3
Good candidate, nervous about risk
A 30-year-old woman with 1 uncomplicated vaginal delivery and 1 cesarean section 3 years prior presents in her third pregnancy for counseling about VBAC.
Her cesarean was performed through a transverse incision in the lower uterine segment for repetitive deep variable decelerations. A friend recently experienced uterine rupture during a trial of labor, resulting in a hysterectomy. She is undecided about future childbearing.
Decision Patient and physician agree on cesarean
With a prior vaginal delivery and a previous cesarean through a low-transverse uterine incision over 18 months ago for an indication that is unlikely to recur, the likelihood of VBAC success is high.
However, the patient was worried by potential risks for uterine rupture, adverse perinatal outcome, and loss of future reproductive potential. After considering the risks and benefits, she requested a repeat cesarean delivery.
After fully counseling the patient on the risks and benefits of VBAC versus elective repeat cesarean, a management plan was made and documented.
The patient underwent an uncomplicated cesarean section at 39 weeks and delivered a healthy baby.
VBAC is not an option where facilities fall short
Despite meeting VBAC criteria for previous incision or pelvic adequacy, many US women do not have the option of a trial of labor. The reason: the need for obstetric care providers throughout active labor and the ability to perform an emergency cesarean.1 As a result, many midwives and family practitioners can no longer care for VBAC patients independently.
Continuous monitoring is a must
It is the potential for uterine rupture that places patients at risk for unfavorable obstetric outcomes—and rupture can be hard to predict. A nonreassuring fetal heart rate is the most frequent sign.1 Others are uterine or abdominal pain, vaginal bleeding, loss of station of the presenting part, and hypovolemia.1
Continuous electronic monitoring of the fetal heart has the potential to detect nonreassuring events earlier than intermittent auscultation. Thus, continuous fetal heart rate monitoring has become the standard for women attempting VBAC. When it is unavailable, VBAC should not be offered.
Also crucial: Anesthesiology
ACOG recommends that anesthesia and other personnel be on hand in case emergency cesarean is warranted.1 While teaching hospitals and large referral centers are constantly staffed with obstetricians and anesthesiologists, birthing centers and smaller community-based hospitals often lack such coverage. As a result, some physicians and hospitals have withdrawn VBAC as an option
Reducing medicolegal risk
When a trial of labor results in uterine rupture or other adverse outcomes, the patient is more likely to sue. Informed consent and thorough documentation of the VBAC decision are crucial and should include37:
- Appropriate discussion of maternal and perinatal risks and benefits, and documentation of this exchange.
- A clear statement of the woman’s intention to undergo a trial of labor after cesarean delivery.
- If possible, documentation of previous uterine scar on the prenatal record.
- Appropriate counseling about the increased risk of rupture when labor is induced with oxytocin, and documentation of this discussion.
- Counseling about the increased risk of rupture when a trial of labor follows a previous cesarean by less than 19 months.
- Discussion about decreased likelihood of success if the woman is obese, is of advanced age, or has not had a prior vaginal birth.
Is VBAC availability better for health and happiness?
Many women want the option of a trial of labor after cesarean because it affords them the opportunity to experience vaginal delivery. Women who have undergone both cesarean and vaginal deliveries usually opt for a trial of labor in their next pregnancy.38 When a physician or hospital eliminates VBAC as an option, it can lead to patient dissatisfaction—as well as loss of revenue if a woman seeks care elsewhere.
Risk of placenta accreta
If elective repeat cesarean were the only option, the incidence of placenta accreta would increase over time.
Placenta accreta is strongly linked to placenta previa, a condition recognized to increase as the number of previous cesarean sections rises.39,40 A woman with 2 prior cesareans has a 2% incidence of placenta previa; nearly half of these cases are associated with placenta accreta.41 As a result, complications of accreta such as maternal death, need for substantial transfusion, postoperative infection, and intraoperative urinary tract injuries would be expected to increase if VBAC were abandoned.42
For this reason, it is important to ask about the patient’s childbearing goals. If a large family is planned, the potential risk of placenta accreta should be explained.
Assess for accreta. All patients with a prior cesarean section require careful evaluation of placental location and assessment for possible accreta should placenta previa or a low-lying placenta be identified prenatally.
I have found both ultrasound and magnetic resonance imaging useful in recognizing accreta, allowing for adequate preoperative preparation and more favorable outcomes. If accreta is not detected until the time of elective repeat cesarean, it can be life-threatening for the patient.
Should we abandon VBAC?
An unfortunate result of the initiatives promoting VBAC in the 1980s and 90s was a higher rate of uterine rupture, since many women with previous cesarean were strongly encouraged—even required—to undergo a trial of labor. Now that elective repeat cesareans are again on the rise, the risk of rupture should diminish due to better VBAC patient selection, but will probably remain substantially higher than for repeat cesarean.
What exactly is the risk of rupture?
In 1 population-based, retrospective cohort analysis25 involving 20,095 women with 1 previous cesarean section, researchers found a rate of uterine rupture of 5.2 per 1,000 women when labor was spontaneous, compared with 1.6 per 1,000 women who underwent elective repeat cesarean without labor. For women having labor induced with prostaglandins or by other means, the rates were 24.5 and 7.7 per 1,000, respectively.
In the same study, the relative risk of uterine rupture was 3.3 for women presenting in spontaneous labor, compared with those who underwent repeat cesarean without labor; it was 15.6 and 4.9 for women whose labor was induced with prostaglandins or by other means, respectively. The rate of infant mortality was 5.5% in cases involving uterine rupture, compared with 0.5% without rupture.25
Note that this study covered the years 1987 through 1996—and thus predated ACOG rules requiring round-the-clock obstetric and anesthesia care, and those barring prostaglandins for labor induction.
Perinatal death more likely with VBAC, but absolute risk is low
A separate population-based, retrospective, cohort study18 focused on different outcomes: intrapartum stillbirth or neonatal death. This study involved 313,238 singleton births at 37 to 43 weeks’ gestation with the fetus in a cephalic presentation.
Among the women opting for VBAC, the overall rate of delivery-related perinatal death was 12.9 per 10,000 women. This was approximately 11 times greater than the risk associated with planned repeat cesarean, more than twice the risk associated with labor in multiparous women, and similar to the risk among nulliparous women in labor. However, in absolute terms, the risk of perinatal death associated with a trial of labor and uterine rupture was low: 1 in 2,200.18
What’s the bottom line?
Are findings such as these reason to abandon VBAC? Not necessarily. VBAC success rates range from 60% to 80%, and a 1991 meta-analysis43 of more than 30 US studies found lower maternal febrile morbidity after a trial of labor than after repeat cesarean, and no differences between the 2 approaches in uterine dehiscence, rupture, or perinatal mortality.
A more recent meta-analysis9 of international studies involving 47,682 women found a uterine rupture rate of 0.4% for women undergoing a trial of labor versus 0.2% for those having elective repeat cesarean. A later meta-analysis, also international, found an overall uterine rupture rate of 6.2 per 1,000 women attempting VBAC, with a perinatal mortality rate of 0.4 per 1,000. Perinatal mortality was significantly lower among US studies.6
Nevertheless, when it comes to VBAC, absolute risks are low, and planned repeat cesarean does not eliminate them entirely. Elective cesarean carries a risk of maternal death up to 2.8 times that of vaginal delivery, though absolute risk is low.44
Thus, when patients are carefully selected and fully informed of benefits and risks, VBAC should remain an available option.
The author reports no relevant financial relationships.
- Selection criteria useful for identifying candidates for VBAC include: a limit of 1 prior low-transverse cesarean, clinically adequate pelvis, no other uterine scars or previous rupture, and no contraindications.
- Offer VBAC only if obstetric care and anesthesiology are available throughout active labor, in case emergency cesarean is necessary.
- Single-layer uterine closure may increase the risk of rupture during subsequent labors.
- Epidural anesthesia is safe for women undergoing a trial of labor.
The new bulletin reaffirms the previous recommendation that obstetric and anesthesia personnel be immediately available throughout active labor, in case emergency cesarean is necessary.
VBAC is still within the standard of care, but rates were declining even before the new bulletin was released: from a high of 28.3% in 1996 to 12.6% in 2002.2
Benefits of VBAC may outweigh the risks in most women with 1 previous low-transverse cesarean,3 but even with optimal facilities and personnel, numerous factors warrant special caution, according to recent studies I’ll review in this article.
Recent studies of risks and benefits
No randomized trials. ACOG notes,1 “Despite thousands of citations in the world’s literature, there are currently no randomized trials comparing maternal or neonatal outcomes for both repeat cesarean delivery and VBAC.”
Success rates are similar for gravidas with previous cesarean for a nonrecurring indication and those with no previous cesarean.4-6
Uterine rupture is more likely during a trial of labor, but the rate is usually below 1%.7-9
Other limiting factors may include labor augmentation and induction, maternal obesity, gestational age beyond 40 weeks, birth weight over 4,000 g, and an interdelivery interval of less than 19 months.10-17
When a trial of labor fails, women face a heightened risk of uterine rupture, hysterectomy, transfusion, and endometritis.3,4,9
Perinatal death is more likely during VBAC than planned repeat cesarean, although the death rate is usually less than 1%.3,8,9,18
Indications and contraindications
The TABLE outlines potential candidates, ineligible gravidas, resources needed, and situations that warrant caution.
Don’t assume: Check the previous operative note
It is all too easy to presume that a previous cesarean section at term was performed through a transverse incision in the lower uterine segment.
While this may be true in the majority of cases, the actual operative note may reveal information relevant to the delivery decision: an extensive tear of the uterine incision, previously unrecognized uterine anomalies, or the need to perform a classical or T-shaped incision to facilitate delivery of the infant.
For these reasons, review the actual operative report whenever possible before a trial of labor.
2 prior low-transverse incisions
While this is not an absolute contraindication to VBAC, in today’s cautious climate ACOG recommends VBAC proceed only when there is also a history of successful vaginal delivery.1,19 Otherwise, women with 2 or more previous cesareans should undergo repeat abdominal birth.
Prior low-vertical incision
Although successful VBACs have been reported in women with a prior low-vertical uterine incision, many experts feel that these incisions often extend superiorly into the upper uterus and thus increase the likelihood of uterine rupture in subsequent labors.20,21
Greater risk with single-layer closure
Single-layer uterine closure appears to increase the likelihood of rupture during subsequent labors.22 As a result, many physicians have returned to 2-layer closure of the lower transverse uterine incision. It is unclear whether single-layer closure is a contraindication to subsequent labor, but it does warrant caution due to a 4-fold increase in the risk of rupture.22
Discourage closely spaced gestations
The shorter the interval between deliveries, the more likely is uterine rupture during a trial of labor.23,24 For those considering a subsequent VBAC, I recommend trying to space their next delivery at least 18 months after cesarean birth.
Labor induction increases risk
Spontaneous labor leads to successful VBAC more often than does labor induction or augmentation. In addition, a recent study found 5 times the risk of uterine rupture when oxytocin was used to induce labor, compared with elective repeat cesarean—although the rate of rupture was less than 1% in both groups.25
The use of prostaglandins in labor induction greatly increases the risk of rupture, with rates of 24.5 per 1,000 reported, compared with 5.2 per 1,000 in women with spontaneous labor.26 ACOG strongly discourages the use of prostaglandin cervical ripening agents in labor inductions.26
Seek out other factors
Women who initially appear eligible may harbor other characteristics or conditions that warrant special attention.15,26-28
External cephalic version. Although 1 study29 concluded it is effective in women undergoing a trial of labor after cesarean, vigilance is recommended.
Twin gestations. Two retrospective studies involving a total of 45 women found VBAC to be safe in twin gestations. Because of the limited number of women studied and the lack of randomized, controlled trials, caution is strongly advised.30,31
Macrosomia. The rate of uterine rupture rises in women who have not had a previous vaginal delivery.27
Postdates. Although VBAC is less likely to succeed after 40 weeks’ gestation, the risk of uterine rupture increases only with induction of labor.11
Analgesia. Women undergoing a trial of labor can receive epidural anesthesia without increasing the risk of rupture or failed VBAC and without obscuring the signs and symptoms of uterine rupture.32,33 In fact, as ACOG notes, effective pain relief may encourage more women to try VBAC.1
Previous vaginal delivery. Women who have delivered vaginally are more likely to succeed at VBAC—by a factor of 9 to 28—than those who have not.34,35
Other conditions such as maternal obesity and advanced age should be evaluated in light of the patient’s overall risk-benefit profile. Although caution is recommended, definitive data are lacking.
TABLE
Criteria for trial of labor
| QUALIFICATIONS |
| 1 prior low-transverse cesarean section |
| Clinically adequate pelvis |
| No other uterine scars |
| DISQUALIFICATIONS |
| Prior classical or T-shaped uterine incision |
| Multiple uterine incisions |
| Previous uterine rupture |
| Contracted pelvis |
| Contraindications to vaginal birth |
| REQUIREMENTS THROUGHOUT ACTIVE LABOR |
| Obstetrician immediately available |
| Continuous electronic monitoring of the fetal heart rate |
| Personnel skilled in interpreting fetal tracings |
| Anesthesia for emergency cesarean |
| Physician qualified for emergency cesarean |
| PRECAUTIONS |
| Unknown uterine scars |
| Prior low vertical uterine incision |
| Uterine malformations |
| Prior single-layer uterine closure |
| Short interdelivery interval |
| Need for labor induction |
| Need for external cephalic version |
| Twin gestation |
| Suspected macrosomia |
| Maternal obesity |
| Postdates |
| Advanced maternal age |
| No prior vaginal delivery |
| Source: ACOG1 |
Prognostic formulas
One decision analysis36 concluded that VBAC is a reasonable option when the chance of success exceeds 50% and the desire for future pregnancy is 10% to 20% or more. Although scoring systems have been proposed to predict the likelihood of success, individualized assessment of each patient is ideal. (See “Case by case: Adding up the decisive factors”.)
CASE 1
A single cesarean and a healthy fetus
After her obstetrician encourages a repeat cesarean at 39 weeks’ gestation, a 39-year-old gravida seeks a second opinion. Her obstetric history includes a remote first-trimester miscarriage and a cesarean section, 2 years prior, of vertex-vertex twins at 36 weeks for arrest of labor at 8 cm. Tubal ligation is planned after delivery.
The previous operative report indicates that a low-transverse uterine incision was repaired in 2 layers. The patient plans to deliver at a local community hospital without full-time, in-hospital anesthesiology services.
This pregnancy has been uncomplicated, and ultrasound has confirmed a normally grown fetus in vertex presentation with a fundal placenta. The patient is considering vaginal birth after cesarean (VBAC).
Decision Multiple factors make VBAC unwise
This patient is a poor candidate due to advanced maternal age, no prior vaginal birth, and the previous cesarean for failure to progress. Lack of round-the-clock anesthesiology at her chosen hospital contraindicates trial of labor.1
Her request for postpartum sterilization also makes repeat cesarean wiser.
After these risks are explained, the patient accepts the recommendation for elective repeat cesarean.
CASE 2
Breech presentation, short interdelivery interval
A 28-year-old gravida has a breech presentation at 37 weeks. She has had 3 spontaneous vaginal deliveries and 1 cesarean section at term for a nonreassuring fetal tracing in labor. The cesarean was 14 months ago. The operative note is not available. She says she was told future vaginal deliveries would be possible.
She plans to have a large family.
Apart from the breech presentation, this pregnancy has been uneventful. The patient requests external cephalic version prior to a trial of labor.
Decision Take future plans into account
Placenta previa, accreta, adhesions, and intraoperative injuries are recognized risks in patients with a higher number of cesarean deliveries.
In this case, breech presentation, a short interdelivery interval, and an undocumented uterine incision warrant caution. Given that the patient’s cesarean section was performed at term in the United States, and that she was told she would be able to have a subsequent vaginal birth, she underwent a successful external cephalic version in the delivery room. She had an uneventful spontaneous vaginal delivery 3 weeks later.
CASE 3
Good candidate, nervous about risk
A 30-year-old woman with 1 uncomplicated vaginal delivery and 1 cesarean section 3 years prior presents in her third pregnancy for counseling about VBAC.
Her cesarean was performed through a transverse incision in the lower uterine segment for repetitive deep variable decelerations. A friend recently experienced uterine rupture during a trial of labor, resulting in a hysterectomy. She is undecided about future childbearing.
Decision Patient and physician agree on cesarean
With a prior vaginal delivery and a previous cesarean through a low-transverse uterine incision over 18 months ago for an indication that is unlikely to recur, the likelihood of VBAC success is high.
However, the patient was worried by potential risks for uterine rupture, adverse perinatal outcome, and loss of future reproductive potential. After considering the risks and benefits, she requested a repeat cesarean delivery.
After fully counseling the patient on the risks and benefits of VBAC versus elective repeat cesarean, a management plan was made and documented.
The patient underwent an uncomplicated cesarean section at 39 weeks and delivered a healthy baby.
VBAC is not an option where facilities fall short
Despite meeting VBAC criteria for previous incision or pelvic adequacy, many US women do not have the option of a trial of labor. The reason: the need for obstetric care providers throughout active labor and the ability to perform an emergency cesarean.1 As a result, many midwives and family practitioners can no longer care for VBAC patients independently.
Continuous monitoring is a must
It is the potential for uterine rupture that places patients at risk for unfavorable obstetric outcomes—and rupture can be hard to predict. A nonreassuring fetal heart rate is the most frequent sign.1 Others are uterine or abdominal pain, vaginal bleeding, loss of station of the presenting part, and hypovolemia.1
Continuous electronic monitoring of the fetal heart has the potential to detect nonreassuring events earlier than intermittent auscultation. Thus, continuous fetal heart rate monitoring has become the standard for women attempting VBAC. When it is unavailable, VBAC should not be offered.
Also crucial: Anesthesiology
ACOG recommends that anesthesia and other personnel be on hand in case emergency cesarean is warranted.1 While teaching hospitals and large referral centers are constantly staffed with obstetricians and anesthesiologists, birthing centers and smaller community-based hospitals often lack such coverage. As a result, some physicians and hospitals have withdrawn VBAC as an option
Reducing medicolegal risk
When a trial of labor results in uterine rupture or other adverse outcomes, the patient is more likely to sue. Informed consent and thorough documentation of the VBAC decision are crucial and should include37:
- Appropriate discussion of maternal and perinatal risks and benefits, and documentation of this exchange.
- A clear statement of the woman’s intention to undergo a trial of labor after cesarean delivery.
- If possible, documentation of previous uterine scar on the prenatal record.
- Appropriate counseling about the increased risk of rupture when labor is induced with oxytocin, and documentation of this discussion.
- Counseling about the increased risk of rupture when a trial of labor follows a previous cesarean by less than 19 months.
- Discussion about decreased likelihood of success if the woman is obese, is of advanced age, or has not had a prior vaginal birth.
Is VBAC availability better for health and happiness?
Many women want the option of a trial of labor after cesarean because it affords them the opportunity to experience vaginal delivery. Women who have undergone both cesarean and vaginal deliveries usually opt for a trial of labor in their next pregnancy.38 When a physician or hospital eliminates VBAC as an option, it can lead to patient dissatisfaction—as well as loss of revenue if a woman seeks care elsewhere.
Risk of placenta accreta
If elective repeat cesarean were the only option, the incidence of placenta accreta would increase over time.
Placenta accreta is strongly linked to placenta previa, a condition recognized to increase as the number of previous cesarean sections rises.39,40 A woman with 2 prior cesareans has a 2% incidence of placenta previa; nearly half of these cases are associated with placenta accreta.41 As a result, complications of accreta such as maternal death, need for substantial transfusion, postoperative infection, and intraoperative urinary tract injuries would be expected to increase if VBAC were abandoned.42
For this reason, it is important to ask about the patient’s childbearing goals. If a large family is planned, the potential risk of placenta accreta should be explained.
Assess for accreta. All patients with a prior cesarean section require careful evaluation of placental location and assessment for possible accreta should placenta previa or a low-lying placenta be identified prenatally.
I have found both ultrasound and magnetic resonance imaging useful in recognizing accreta, allowing for adequate preoperative preparation and more favorable outcomes. If accreta is not detected until the time of elective repeat cesarean, it can be life-threatening for the patient.
Should we abandon VBAC?
An unfortunate result of the initiatives promoting VBAC in the 1980s and 90s was a higher rate of uterine rupture, since many women with previous cesarean were strongly encouraged—even required—to undergo a trial of labor. Now that elective repeat cesareans are again on the rise, the risk of rupture should diminish due to better VBAC patient selection, but will probably remain substantially higher than for repeat cesarean.
What exactly is the risk of rupture?
In 1 population-based, retrospective cohort analysis25 involving 20,095 women with 1 previous cesarean section, researchers found a rate of uterine rupture of 5.2 per 1,000 women when labor was spontaneous, compared with 1.6 per 1,000 women who underwent elective repeat cesarean without labor. For women having labor induced with prostaglandins or by other means, the rates were 24.5 and 7.7 per 1,000, respectively.
In the same study, the relative risk of uterine rupture was 3.3 for women presenting in spontaneous labor, compared with those who underwent repeat cesarean without labor; it was 15.6 and 4.9 for women whose labor was induced with prostaglandins or by other means, respectively. The rate of infant mortality was 5.5% in cases involving uterine rupture, compared with 0.5% without rupture.25
Note that this study covered the years 1987 through 1996—and thus predated ACOG rules requiring round-the-clock obstetric and anesthesia care, and those barring prostaglandins for labor induction.
Perinatal death more likely with VBAC, but absolute risk is low
A separate population-based, retrospective, cohort study18 focused on different outcomes: intrapartum stillbirth or neonatal death. This study involved 313,238 singleton births at 37 to 43 weeks’ gestation with the fetus in a cephalic presentation.
Among the women opting for VBAC, the overall rate of delivery-related perinatal death was 12.9 per 10,000 women. This was approximately 11 times greater than the risk associated with planned repeat cesarean, more than twice the risk associated with labor in multiparous women, and similar to the risk among nulliparous women in labor. However, in absolute terms, the risk of perinatal death associated with a trial of labor and uterine rupture was low: 1 in 2,200.18
What’s the bottom line?
Are findings such as these reason to abandon VBAC? Not necessarily. VBAC success rates range from 60% to 80%, and a 1991 meta-analysis43 of more than 30 US studies found lower maternal febrile morbidity after a trial of labor than after repeat cesarean, and no differences between the 2 approaches in uterine dehiscence, rupture, or perinatal mortality.
A more recent meta-analysis9 of international studies involving 47,682 women found a uterine rupture rate of 0.4% for women undergoing a trial of labor versus 0.2% for those having elective repeat cesarean. A later meta-analysis, also international, found an overall uterine rupture rate of 6.2 per 1,000 women attempting VBAC, with a perinatal mortality rate of 0.4 per 1,000. Perinatal mortality was significantly lower among US studies.6
Nevertheless, when it comes to VBAC, absolute risks are low, and planned repeat cesarean does not eliminate them entirely. Elective cesarean carries a risk of maternal death up to 2.8 times that of vaginal delivery, though absolute risk is low.44
Thus, when patients are carefully selected and fully informed of benefits and risks, VBAC should remain an available option.
The author reports no relevant financial relationships.
1. American College of Obstetricians and Gynecologists. ACOG Practice Bulletin #54: Vaginal Birth After Previous Cesarean Delivery. Washington, DC: ACOG; July 2004.
2. Martin JA, Hamilton BE, Sutton PD, Ventura SJ, Menacker F, Munson ML. Births: final data for 2002. Natl Vital Stat Rep. 2003;52(10):1-113.
3. Rageth JC, Juzi C, Grossenbacher H. for the Swiss Working Group of Obstetric and Gynecologic Institutions. Delivery after previous cesarean: a risk evaluation. Obstet Gynecol. 1999;93:332-337.
4. Hibbard JU, Ismail MA, Wang Y, Te C, Karrison T, Ismail MA. Failed vaginal birth after a cesarean section: how risky is it? I. Maternal morbidity. Am J Obstet Gynecol. 2001;184:1365-1371;discussion 1371–1373.
5. Bujold E, Gauthier RJ. Should we allow a trial of labor after a previous cesarean for dystocia in the second stage of labor? Obstet Gynecol. 2001;98:652-655.
6. Chauhan SP, Martin JN, Jr, Henrichs CE, Morrison JC, Magann EF. Maternal and perinatal complications with uterine rupture in 142,075 patients who attempted vaginal birth after cesarean delivery: a review of the literature. Am J Obstet Gynecol. 2003;189:408-417.
7. Gregory KD, Korst LM, Cane P, Platt LD, Kahn K. Vaginal birth after cesarean and uterine rupture rates in California. Obstet Gynecol. 1999;94:985-989.
8. Kieser KE, Baskett TF. A 10-year population-based study of uterine rupture. Obstet Gynecol. 2002;100:749-753.
9. Mozurkewich EL, Hutton EK. Elective repeat cesarean delivery versus trial of labor: a meta-analysis of the literature from 1989 to 1999. Am J Obstet Gynecol. 2000;183:1187-1197.
10. Zelop CM, Shipp TD, Repke JT, Cohen A, Lieberman E. Outcomes of a trial of labor following previous cesarean delivery among women with fetuses weighing >4,000 g. Am J Obstet Gynecol. 2001;185:903-905.
11. Zelop CM, Shipp TD, Cohen A, Repke JT, Lieberman E. Trial of labor after 40 weeks’ gestation in women with prior cesarean. Obstet Gynecol. 2001;97:391-393.
12. Macones GA, Hausman N, Edelstein R, Stamilio DM, Marder SJ. Predicting outcomes of trials of labor in women attempting vaginal birth after cesarean delivery: a comparison of multivariate methods with neural networks. Am J Obstet Gynecol. 2001;184:409-413.
13. Ravasia DJ, Wood SL, Pollard JK. Uterine rupture during induced trial of labor among women with previous cesarean delivery. Am J Obstet Gynecol. 2000;183:1176-1179.
14. Sims EJ, Newman RB, Hulsey TC. Vaginal birth after cesarean: to induce or not to induce. Am J Obstet Gynecol. 2001;184:1122-1124.
15. Chauhan SP, Magann EF, Carroll CS, Barrilleaux PS, Scardo JA, Marttin JN, Jr. Mode of delivery for the morbidly obese with prior cesarean delivery: vaginal versus repeat cesarean section. Am J Obstet Gynecol. 2001;185:349-354.
16. Carroll CS, Sr, Magann EF, Chauhan SP, Klauser CK, Morrison JC. Vaginal birth after cesarean section versus elective repeat cesarean delivery: weight-based outcomes. Am J Obstet Gynecol. 2003;188:1516-1520;discussion 1520–1522.
17. Huang WH, Nakashima DK, Rumney PJ, Keegan KA, Jr, Chan K. Interdelivery interval and the success of vaginal birth after cesarean delivery. Obstet Gynecol. 2002;99:41-44.
18. Smith GC, Pell JP, Cameron AD, Dobbie R. Risk of perinatal death associated with labor after previous cesarean delivery in uncomplicated term pregnancies. JAMA. 2002;287:2684-2690.
19. Bretelle F, Cravello L, Shojai R, Roger V, D’Ercole C, Blanc B. Vaginal birth following two previous cesarean sections. Eur J Obstet Gynecol Reprod Biol. 2001;94:23-26.
20. Shipp TD, Zelop CM, Repke JT, Cohen A, Caughey AB, Lieberman E. Intrapartum uterine rupture and dehiscence in patients with prior lower uterine segment vertical and transverse incisions. Obstet Gynecol. 1999;94:735-740.
21. Naef RW, Ray MA, Chauhan SP, Roach H, Blake PG, Martin JN. Trial of labor after cesarean delivery with a lower-segment, vertical uterine incision: is it safe? Am J Obstet Gynecol. 1995;172:1666-1673.
22. Bujold E, Mehta SH, Bujold C, Gauthier RJ. Interdelivery interval and uterine rupture. Am J Obstet Gynecol. 2002;187:1199-1202.
23. Shipp TD, Zelop CM, Repke JT, Cohen A, Lieberman E. Interdelivery interval and risk of symptomatic uterine rupture. Obstet Gynecol. 2001;97:175-177.
24. Esposito MA, Menihan CA, Malee MP. Association of interpregnancy interval with uterine scar failure in labor: a case control study. Am J Obstet Gynecol. 2000;183:1180-1183.
25. Lydon-Rochelle M, Holt VL, Easterling TR, Martin DP. Risk of uterine rupture during labor among women with a prior cesarean delivery. N Engl J Med. 2001;345:3-8.
26. American College of Obstetricians and Gynecologists, Committee on Obstetric Practice. Committee Opinion: Induction of labor for vaginal birth after cesarean delivery. Obstet Gynecol. 2002;99:679-680.
27. Elkousy MA, Sammel M, Stevens E, Peipert JF, Macones G. The effect of birth weight on vaginal birth after cesarean delivery success rates. Am J Obstet Gynecol. 2003;188:824-830.
28. Zelop CM, Shipp TD, Repke JT, Cohen A, Lieberman E. Effects of previous vaginal delivery on the risk of uterine rupture during a subsequent trial of labor. Am J Obstet Gynecol. 2000;183:1184-1186.
29. Flamm BL, Fried MW, Lonky NM, Giles WS. External cephalic version after previous cesarean section. Am J Obstet Gynecol. 1991;165:370-372.
30. Myles T. Vaginal birth of twins after a previous cesarean section. J Matern Fetal Med. 2001;10:171-174.
31. Sansregret A, Bujold E, Gauthier RJ. Twin delivery after a previous cesarean: a 12-year experience. J Obstet Gynaecol Can. 2003;25:294-298.
32. Johnson C, Oriol N. The role of epidural anesthesia in trial of labor. Reg Anesth. 1990;15:304-308.
33. Sakala EP, Kaye S, Murray RD, Munson LJ. Epidural analgesia. Effect on the likelihood of a successful trial of labor after cesarean section. J Reprod Med. 1990;35:886-890.
34. Flamm BL. Once a cesarean, always a controversy. Obstet Gynecol. 1997;90:312-315.
35. McNally OM, Turner MJ. Induction of labor after 1 previous caesarean section. Aust N Z J Obstet Gynaecol. 1999;39:425-429.
36. Mankuta DD, Leshno MM, Menasche MM, Brezis MM. Vaginal birth after cesarean section: trial of labor or repeat cesarean section? A decision analysis. Am J Obstet Gynecol. 2003;189:714-719.
37. Martel MJ, MacKinnon CJ. Clinical Practice Obstetrics Committee of the Society of Obstetricians and Gynaecologists of Canada. Guidelines for vaginal birth after previous Caesarean birth. J Obstet Gynaecol Can. 2004;26:660-683.
38. McMahon MJ, Luther ER, Bowes WA, Olshan AF. Comparison of a trial of labor with an elective second section. N Engl J Med. 1996;335:689-695.
39. Ananth CV, Smulian JC, Vintzileos AM. The association of placenta previa with history of cesarean delivery and abortion: a metaanalysis. Am J Obstet Gynecol. 1997;177:1071-1078.
40. Miller DA, Chollet JA, Goodwin TM. Clinical risk factors for placenta previa-placenta accreta. Am J Obstet Gynecol. 1997;177:210-214.
41. Clark SL, Koonings PP, Phelan JP. Placenta previa/accreta and prior cesarean section. Obstet Gynecol. 1985;66:89-92.
42. O’Brien JM, Barton JR, Donaldson ES. The management of placenta percreta: conservative and operative strategies. Am J Obstet Gynecol. 1996;175:1632-1638.
43. Rosen MG, Dickinson JC, Westhoff CL. Vaginal birth after cesarean: a meta-analysis of morbidity and mortality. Obstet Gynecol. 1991;77:465-470.
44. Hall MH, Bewley S. Maternal mortality and mode of delivery. Lancet. 1999;354:776.-
1. American College of Obstetricians and Gynecologists. ACOG Practice Bulletin #54: Vaginal Birth After Previous Cesarean Delivery. Washington, DC: ACOG; July 2004.
2. Martin JA, Hamilton BE, Sutton PD, Ventura SJ, Menacker F, Munson ML. Births: final data for 2002. Natl Vital Stat Rep. 2003;52(10):1-113.
3. Rageth JC, Juzi C, Grossenbacher H. for the Swiss Working Group of Obstetric and Gynecologic Institutions. Delivery after previous cesarean: a risk evaluation. Obstet Gynecol. 1999;93:332-337.
4. Hibbard JU, Ismail MA, Wang Y, Te C, Karrison T, Ismail MA. Failed vaginal birth after a cesarean section: how risky is it? I. Maternal morbidity. Am J Obstet Gynecol. 2001;184:1365-1371;discussion 1371–1373.
5. Bujold E, Gauthier RJ. Should we allow a trial of labor after a previous cesarean for dystocia in the second stage of labor? Obstet Gynecol. 2001;98:652-655.
6. Chauhan SP, Martin JN, Jr, Henrichs CE, Morrison JC, Magann EF. Maternal and perinatal complications with uterine rupture in 142,075 patients who attempted vaginal birth after cesarean delivery: a review of the literature. Am J Obstet Gynecol. 2003;189:408-417.
7. Gregory KD, Korst LM, Cane P, Platt LD, Kahn K. Vaginal birth after cesarean and uterine rupture rates in California. Obstet Gynecol. 1999;94:985-989.
8. Kieser KE, Baskett TF. A 10-year population-based study of uterine rupture. Obstet Gynecol. 2002;100:749-753.
9. Mozurkewich EL, Hutton EK. Elective repeat cesarean delivery versus trial of labor: a meta-analysis of the literature from 1989 to 1999. Am J Obstet Gynecol. 2000;183:1187-1197.
10. Zelop CM, Shipp TD, Repke JT, Cohen A, Lieberman E. Outcomes of a trial of labor following previous cesarean delivery among women with fetuses weighing >4,000 g. Am J Obstet Gynecol. 2001;185:903-905.
11. Zelop CM, Shipp TD, Cohen A, Repke JT, Lieberman E. Trial of labor after 40 weeks’ gestation in women with prior cesarean. Obstet Gynecol. 2001;97:391-393.
12. Macones GA, Hausman N, Edelstein R, Stamilio DM, Marder SJ. Predicting outcomes of trials of labor in women attempting vaginal birth after cesarean delivery: a comparison of multivariate methods with neural networks. Am J Obstet Gynecol. 2001;184:409-413.
13. Ravasia DJ, Wood SL, Pollard JK. Uterine rupture during induced trial of labor among women with previous cesarean delivery. Am J Obstet Gynecol. 2000;183:1176-1179.
14. Sims EJ, Newman RB, Hulsey TC. Vaginal birth after cesarean: to induce or not to induce. Am J Obstet Gynecol. 2001;184:1122-1124.
15. Chauhan SP, Magann EF, Carroll CS, Barrilleaux PS, Scardo JA, Marttin JN, Jr. Mode of delivery for the morbidly obese with prior cesarean delivery: vaginal versus repeat cesarean section. Am J Obstet Gynecol. 2001;185:349-354.
16. Carroll CS, Sr, Magann EF, Chauhan SP, Klauser CK, Morrison JC. Vaginal birth after cesarean section versus elective repeat cesarean delivery: weight-based outcomes. Am J Obstet Gynecol. 2003;188:1516-1520;discussion 1520–1522.
17. Huang WH, Nakashima DK, Rumney PJ, Keegan KA, Jr, Chan K. Interdelivery interval and the success of vaginal birth after cesarean delivery. Obstet Gynecol. 2002;99:41-44.
18. Smith GC, Pell JP, Cameron AD, Dobbie R. Risk of perinatal death associated with labor after previous cesarean delivery in uncomplicated term pregnancies. JAMA. 2002;287:2684-2690.
19. Bretelle F, Cravello L, Shojai R, Roger V, D’Ercole C, Blanc B. Vaginal birth following two previous cesarean sections. Eur J Obstet Gynecol Reprod Biol. 2001;94:23-26.
20. Shipp TD, Zelop CM, Repke JT, Cohen A, Caughey AB, Lieberman E. Intrapartum uterine rupture and dehiscence in patients with prior lower uterine segment vertical and transverse incisions. Obstet Gynecol. 1999;94:735-740.
21. Naef RW, Ray MA, Chauhan SP, Roach H, Blake PG, Martin JN. Trial of labor after cesarean delivery with a lower-segment, vertical uterine incision: is it safe? Am J Obstet Gynecol. 1995;172:1666-1673.
22. Bujold E, Mehta SH, Bujold C, Gauthier RJ. Interdelivery interval and uterine rupture. Am J Obstet Gynecol. 2002;187:1199-1202.
23. Shipp TD, Zelop CM, Repke JT, Cohen A, Lieberman E. Interdelivery interval and risk of symptomatic uterine rupture. Obstet Gynecol. 2001;97:175-177.
24. Esposito MA, Menihan CA, Malee MP. Association of interpregnancy interval with uterine scar failure in labor: a case control study. Am J Obstet Gynecol. 2000;183:1180-1183.
25. Lydon-Rochelle M, Holt VL, Easterling TR, Martin DP. Risk of uterine rupture during labor among women with a prior cesarean delivery. N Engl J Med. 2001;345:3-8.
26. American College of Obstetricians and Gynecologists, Committee on Obstetric Practice. Committee Opinion: Induction of labor for vaginal birth after cesarean delivery. Obstet Gynecol. 2002;99:679-680.
27. Elkousy MA, Sammel M, Stevens E, Peipert JF, Macones G. The effect of birth weight on vaginal birth after cesarean delivery success rates. Am J Obstet Gynecol. 2003;188:824-830.
28. Zelop CM, Shipp TD, Repke JT, Cohen A, Lieberman E. Effects of previous vaginal delivery on the risk of uterine rupture during a subsequent trial of labor. Am J Obstet Gynecol. 2000;183:1184-1186.
29. Flamm BL, Fried MW, Lonky NM, Giles WS. External cephalic version after previous cesarean section. Am J Obstet Gynecol. 1991;165:370-372.
30. Myles T. Vaginal birth of twins after a previous cesarean section. J Matern Fetal Med. 2001;10:171-174.
31. Sansregret A, Bujold E, Gauthier RJ. Twin delivery after a previous cesarean: a 12-year experience. J Obstet Gynaecol Can. 2003;25:294-298.
32. Johnson C, Oriol N. The role of epidural anesthesia in trial of labor. Reg Anesth. 1990;15:304-308.
33. Sakala EP, Kaye S, Murray RD, Munson LJ. Epidural analgesia. Effect on the likelihood of a successful trial of labor after cesarean section. J Reprod Med. 1990;35:886-890.
34. Flamm BL. Once a cesarean, always a controversy. Obstet Gynecol. 1997;90:312-315.
35. McNally OM, Turner MJ. Induction of labor after 1 previous caesarean section. Aust N Z J Obstet Gynaecol. 1999;39:425-429.
36. Mankuta DD, Leshno MM, Menasche MM, Brezis MM. Vaginal birth after cesarean section: trial of labor or repeat cesarean section? A decision analysis. Am J Obstet Gynecol. 2003;189:714-719.
37. Martel MJ, MacKinnon CJ. Clinical Practice Obstetrics Committee of the Society of Obstetricians and Gynaecologists of Canada. Guidelines for vaginal birth after previous Caesarean birth. J Obstet Gynaecol Can. 2004;26:660-683.
38. McMahon MJ, Luther ER, Bowes WA, Olshan AF. Comparison of a trial of labor with an elective second section. N Engl J Med. 1996;335:689-695.
39. Ananth CV, Smulian JC, Vintzileos AM. The association of placenta previa with history of cesarean delivery and abortion: a metaanalysis. Am J Obstet Gynecol. 1997;177:1071-1078.
40. Miller DA, Chollet JA, Goodwin TM. Clinical risk factors for placenta previa-placenta accreta. Am J Obstet Gynecol. 1997;177:210-214.
41. Clark SL, Koonings PP, Phelan JP. Placenta previa/accreta and prior cesarean section. Obstet Gynecol. 1985;66:89-92.
42. O’Brien JM, Barton JR, Donaldson ES. The management of placenta percreta: conservative and operative strategies. Am J Obstet Gynecol. 1996;175:1632-1638.
43. Rosen MG, Dickinson JC, Westhoff CL. Vaginal birth after cesarean: a meta-analysis of morbidity and mortality. Obstet Gynecol. 1991;77:465-470.
44. Hall MH, Bewley S. Maternal mortality and mode of delivery. Lancet. 1999;354:776.-