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VBAC Guidelines: Who is a Candidate for a Trial of Labor after Cesarean Delivery?

While trial of labor after cesarean delivery (TOLAC) may be considered after previous cesarean delivery, it is critical that a thorough review of risks and benefits be undertaken. Decision making should incorporate a woman’s preferences and desires. Key highlights from the most recent ACOG guidance include the following:


Candidates for TOLAC (Level A)

  • Singleton:  One previous low transverse cesarean should be counseled and offered TOLAC
  • Individualize
    • Even if patient not a good candidate but admitted to labor floor in active labor, clinical judgement may be used
    • Good candidates are those where balance of risk (low) and chance of success (high) are acceptable to patient and provider
    • Decisions surrounding TOLAC should include discussion of future pregnancies

NOT Candidates for TOLAC (Level B)

  • Previous classical or “T” incision
  • Prior uterine rupture
    • ACOG states

“…similar to a history of a prior classical cesarean, the suggested timing of delivery between 36 0/7 weeks and 37 0/7 weeks of gestation should be considered but can be individualized based on the clinical situation”

  • Extensive transfundal uterine surgery
  • Contraindication for vaginal delivery (e.g. placenta previa)

More than One Previous Cesarean Section (Level B)

  • Two previous low transverse cesarean should be counseled and offered TOLAC
  • Data limited on >2 previous cesarean sections

Macrosomia (birth weight >4,000 g or 4,500 g)

  • Less likelihood of VBAC but data on rupture inconclusive
  • Isolated macrosomia does ‘not preclude’ TOLAC

Gestational Age > 40 Weeks

  • Less likelihood of VBAC but data on rupture conflicting
  • Gestational age > 40 alone does ‘not preclude’ TOLAC

Previous (documented) Low-Vertical incision (Level B)

  • The few studies on this topic demonstrate similar rate of VBAC success and no consistent evidence of rupture/morbidities
  • Consider limited data but provider and patient may elect TOLAC

Unknown Prior Uterine Incision (Level B)

  • Previous case series reported VBAC success and rupture rates similar to known low transverse scars
  • Women with one previous cesarean, unknown scar, may be candidates for TOLAC if no clinical suspicion for classical incision is apparent (e.g., early preterm)

Twin Gestation

  • Consistent evidence that outcomes are similar to singletons
  • Women with twin gestation and one previous low transverse scar cesarean section are candidates for TOLAC


  • BMI alone is not an absolute contraindication but should be considered an additional risk factor that may lower chance of VBAC
  • Obese women have increased risk related to cesarean section
  • Individualize care

Induction and Augmentation of Labor

  • Induction of labor an option (Level B)
  • Augmentation with oxytocin separate from induction may be used
    • While data does support a dose/response relationship between oxytocin use and rupture, no threshold has been identified and therefore “an upper limit for oxytocin dosage with TOLAC has not been established”
  • Literature review indicates increased risk of rupture with induction or augmentation of labor, although ACOG guidance notes issues related to study design, including a large multi-centered trial (33,699 women)
    • 1.4% risk of rupture for prostaglandins +/- oxytocin
    • 1.1% oxytocin alone
    • 0.9% augmented labor
    • 0.4% spontaneous labor (expectant management and not spontaneous labor is the preferable control group and not available in this study)
    • Secondary analysis
      • Increased risk only in women without a prior vaginal delivery
      • Favorability of cervix unrelated to outcome
      • Dose-response with oxytocin use but no clear threshold for rupture


While there are risks to TOLAC, most are related to complications, such as hemorrhage, that may arise from cesarean section in the setting of an unsuccessful trial of labor. However, TOLAC is still offered to patients as an option due to the significant risks associated with multiple repeat cesarean deliveries. Risks of placenta accreta, cystotomy, bowel injury, ureteral injury, and ileus, the need for postoperative ventilation, intensive care unit admission, hysterectomy, and blood transfusion requiring 4 or more units, and the duration of operative time and hospital stay significantly increase with increasing number of cesarean deliveries. In the NICHD MFMU study (Obstetrics and Gynecology 2006), Placenta accreta was present in 0.24% (1st cesarean sections [CS]) 0.31% (2nd CS), 0.57% (3rd CS), 2.13% (4th CS), 2.33% (5th CS), 6.74% (6 or more CS). Hysterectomy was required in 0.65% (1st CS) 0.42% (2nd CS) (0.90% (3rd CS) 2.41% (4th CS) 3.49% (5th CS) and 8.99% (6 or more CS). In  723 women who had previa in this study, risk for placenta accreta was 3% (1st CS), 11% (2nd CS), 40% (3rd CS) 61% (4th CS), and 67% (5 or more CS).


Clinical Factors and Probability of Success

  • The following factors increase the probability of TOLAC success
    • Prior vaginal delivery
    • Spontaneous labor
  • The following factors decrease the probability of TOLAC success
    • Labor dystocia as the indication for primary cesarean section
    • Increased maternal age
    • Non-white ethnicity
    • Gestational age greater than 40 weeks
    • Maternal obesity
    • Preeclampsia
    • Short inter-pregnancy interval
    • Increased neonatal birthweight
  • VBAC predictive caculators
    • The MFMU Network VBAC calculator has been updated and no longer includes race or ethnicity | The calculator can be found in ‘Learn More – Primary Sources’ 
    • Data derived from Grobman et al. (AJOG, 2021) 
    • The calculator should not be used as the only measure for determining patient management

Note: ACOG addresses the use of VBAC calculators and stresses the importance of shared decision making, highlighting the point that a VBAC calculator is just one aspect of the discussion

Currently, there is no evidence demonstrating improved patient outcomes and therefore

A VBAC calculator score should not be used as a barrier to TOLAC

…some patients and clinicians may prefer to utilize a calculator while others may prefer a more general discussion of options for mode of delivery, review of overall VBAC rates of 60–80% with TOLAC, and consideration of an individual’s obstetric risk factors along with their preferences and goals


  • Cervical Ripening
    • Mechanical dilation and transcervical catheters may be an option
    • Misoprostol should not be used in pregnancies at term for cervical ripening or labor induction in patients who have had a cesarean delivery or major uterine surgery (Level A)
    • Prostaglandins can be considered during 2nd trimester
    • Insufficient evidence to make a definitive recommendation for prostaglandin E2
  • External cephalic version for breech presentation is not contraindicated in women with a prior low transverse uterine scar (Level B)
  • Epidural analgesia for labor may be used as part of TOLAC (Level A)| Not considered necessary
  • No difference in labor curves in women undergoing TOLAC
    • Use similar standards to gauge progress of labor
  • The decision to undergo TOLAC or repeat cesarean section, following counseling, should be made by the patient in consultation with her providers
  • Continuous FHR monitoring recommended (Level B)
    • Evidence lacking that IUPC or fetal scalp electrodes are better than external forms of continuous monitoring
    • IUPC may not help diagnose uterine rupture
  • Document and include in the medical record
    • Review of the counseling session
      • Include the potential risks and benefits of both TOLAC and elective repeat cesarean section
    • Management plan

Additional Highlights from the Canadian Evidence Review and Guidelines (2019)

  • Risk of uterine rupture
    • Baseline risk with TOLAC is 0.47%
    • With induction (not contraindicated), risk of rupture highest >40 weeks gestation
    • Prostaglandin E2 not recommended due to increased risk of rupture
  • Continuous electronic fetal monitoring
    • “Is necessary” because changes in the tracing are “one of the key indicators of the presence of a uterine rupture”
  • Breech presentation
    • Not an absolute contraindication
    • Advise that there is insufficient information to assess TOLAC risks
  • Lower uterine thickness measurements
    • There is relationship between lower uterine thickness and risk of uterine rupture
    • Absolute cut-offs not known at this time
    • Ultrasonographic measurements of the lower uterine segment can not be used to counsel regarding TOLAC
  • Previous surgery with single layer uterine closure
    • Women should be made aware that their is an increased risk of uterine rupture with single vs double uterine closure

Learn More – Primary Sources:

ACOG Practice Bulletin 205:  Vaginal birth after previous cesarean delivery

Maternal morbidity associated with multiple repeat cesarean deliveries

MFMU Network Calculator for VBAC

ACOG Practice Advisory: Counseling Regarding Approach to Delivery After Cesarean and the Use of a Vaginal Birth After Cesarean Calculator

Prediction of vaginal birth after cesarean in term gestations: A calculator without race and ethnicity