VBAC
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VBAC vaginal birth after cesarean eligibility criteria contraindications
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VBAC uterine rupture risk management outcomes trial of labor
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VBAC — Vaginal Birth After Cesarean
Definition
VBAC refers to delivering vaginally after a prior cesarean section. The process of attempting vaginal delivery is called a Trial of Labor After Cesarean (TOLAC). VBAC is the successful outcome of a TOLAC.
Candidacy: Who Is Eligible for TOLAC?
Favorable Criteria
| Factor | Detail |
|---|---|
| Prior uterine incision | Low transverse (low segment) cesarean — the standard recommendation |
| Number of prior cesareans | 1 prior CS (strongest evidence); 2 prior CS (selected candidates, higher risk) |
| Pelvis | Clinically adequate |
| No other uterine scars | No prior classical or T-incision |
| Institution | Ability to perform emergency cesarean (personnel + OR availability) |
| Spontaneous labor | Higher success rate than induced |
VBAC Success Prediction (MFMU Nomogram)
Key predictors of successful VBAC:
- Prior vaginal delivery (especially prior VBAC) — strongest predictor, success rate >85–90%
- Favorable cervical exam on admission
- Spontaneous onset of labor
- Non-recurrent indication for prior CS (e.g., breech, not cephalopelvic disproportion)
- BMI <30
- White or Hispanic ethnicity (per MFMU model — statistical, not used in isolation)
Absolute Contraindications to TOLAC
- Prior classical (vertical) uterine incision or prior uterine rupture
- Prior T-shaped or inverted-T incision
- Prior transmyometrial surgery (e.g., myomectomy entering the cavity)
- Inability to perform emergency cesarean at the delivery site
- Placenta previa or other contraindication to vaginal delivery
Risks
Uterine Rupture — The Central Concern
- Overall risk: ~0.5–0.9% with one prior low transverse CS
- Increases with:
- Prior classical incision: 4–9%
- Oxytocin augmentation: slightly increased risk
- Misoprostol (PGE1) use: contraindicated — significantly increases rupture risk
- Prior uterine rupture: risk up to 6% for lower segment, higher for upper segment rupture
- Short interpregnancy interval (<18 months)
- Single-layer uterine closure (debated)
Signs of Uterine Rupture
- Sudden fetal bradycardia or category III FHR tracing
- Loss of fetal station
- Abrupt cessation of uterine contractions
- Severe abdominal pain (may persist between contractions)
- Maternal hemodynamic instability
Benefits of VBAC
- Avoids repeat cesarean morbidity: placenta accreta spectrum, bowel/bladder injury, adhesions, surgical complications
- Shorter recovery, earlier return to activity
- Reduced risk in future pregnancies (fewer cesareans = fewer placenta accreta spectrum complications)
- No abdominal scar complications
Management of TOLAC
Antepartum
- Thorough counseling with documentation of informed consent
- Review operative report of prior CS to confirm incision type (if available)
- Discuss at 36 weeks; finalize birth plan
Intrapartum
- Continuous electronic fetal monitoring — mandatory
- IV access maintained
- Delivery in a facility with immediate cesarean capability (anesthesia, surgical team)
- Oxytocin augmentation: acceptable but used cautiously
- Misoprostol: contraindicated
- Epidural: not contraindicated; may be offered
- Avoid uterine hyperstimulation
Special Populations
- Twin gestation + TOLAC: not contraindicated per ACOG; selected patients
- Unknown uterine scar: generally treated as low transverse if no records available — institution-dependent
- HIV: VBAC can be offered where viral load <50 copies/mL in absence of obstetric contraindications (Management of HIV in Pregnancy and the Postpartum Period, p. 120)
Success Rates
| Scenario | Approximate VBAC Success |
|---|---|
| Overall TOLAC | 60–80% |
| Prior vaginal delivery | 85–90%+ |
| Prior VBAC | >90% |
| No prior vaginal delivery | ~50–60% |
| Induction of labor | ~50–60% |
Repeat Cesarean vs. TOLAC: Comparative Risks
| Outcome | TOLAC | Elective Repeat CS |
|---|---|---|
| Uterine rupture | ~0.7% | ~0.03% |
| Transfusion | ~1.7% | ~1.0% |
| Hysterectomy | ~0.2% | ~0.3% |
| Maternal mortality | Low, similar | Low, similar |
| NICU admission | Similar | Slightly higher (transient tachypnea) |
| Placenta accreta (future pregnancies) | Lower (fewer CS) | Increases with each CS |
ACOG Position (Practice Bulletin 205, 2019 — reaffirmed)
- TOLAC is a safe and appropriate option for most women with one prior low transverse CS
- Strongly recommends shared decision-making
- Notes that the best outcomes occur at facilities capable of immediate cesarean
- Acknowledges that access disparities exist (many hospitals no longer offer TOLAC)
Key Takeaway
VBAC is a viable, evidence-supported option for appropriately selected patients. The critical variables are the type of prior uterine incision, facility capability, and individual risk factors. Prior vaginal delivery is the single strongest predictor of success. Uterine rupture — though uncommon — is the primary catastrophic risk and mandates continuous intrapartum surveillance.
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