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:
CLINICAL ACTIONS:
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
Obesity
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
SYNOPSIS:
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).
KEY POINTS:
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
CLINICAL CONSIDERATIONS:
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
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