VBAC
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VBAC vaginal birth after cesarean candidacy criteria management
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VBAC uterine rupture risk factors outcomes trial of labor
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VBAC — Vaginal Birth After Cesarean
Definition
VBAC refers to a vaginal delivery in a patient with a prior uterine scar from cesarean section. A Trial of Labor After Cesarean (TOLAC) is the planned attempt to achieve VBAC.
Candidacy — Who Is Eligible for TOLAC?
Favorable Factors
| Factor | Detail |
|---|---|
| Prior cesarean incision | Low transverse uterine incision |
| Number of prior cesareans | 1 (possibly 2 — see below) |
| Indication for prior cesarean | Non-recurring (e.g., breech, fetal distress) |
| Prior vaginal delivery | Especially prior VBAC — most favorable predictor |
| Adequate pelvis | Clinical assessment |
| Gestational age | < 40 weeks (lower success after 41 weeks) |
| Spontaneous labor onset | Higher success than induction |
Contraindications to TOLAC
| Absolute | Relative |
|---|---|
| Prior classic (vertical) uterine incision | ≥ 2 prior cesareans (no prior vaginal delivery) |
| Prior T-shaped or J-shaped incision | Short inter-delivery interval (< 18 months) |
| Prior uterine rupture | Macrosomia (> 4,000–4,500 g) |
| Prior transmyometrial surgery (e.g., myomectomy through cavity) | Unknown uterine scar type |
| Placenta previa / other delivery contraindication | Labor induction (especially prostaglandins) |
Success Rates
- Overall VBAC success rate: 60–80% in properly selected candidates
- Prior vaginal delivery: success rate ~85–90%
- Prior VBAC specifically: success rate ~90%+
- No prior vaginal delivery + unfavorable cervix + induction: success rate ~50% or lower
VBAC Prediction Score (Flamm & Geiger / MFMU model)
Key predictors of success:
- Age < 40
- Prior vaginal delivery (especially prior VBAC)
- Non-recurrent indication for prior cesarean
- Favorable cervical exam on admission
- Spontaneous labor
The Critical Risk: Uterine Rupture
| Parameter | Value |
|---|---|
| Risk with TOLAC (low transverse scar) | 0.5–0.9% (~1 in 150–200) |
| Risk with elective repeat cesarean (ERCS) | ~0.02% (scar dehiscence, not true rupture) |
| Risk with prior classic incision | 4–9% |
| Risk with prior uterine rupture | 6–32% |
Signs of Uterine Rupture
- Sudden loss of fetal station
- Fetal bradycardia / category III FHR tracing
- Loss of uterine contractions
- Maternal tachycardia, hypotension
- Sudden cessation of previously effective contractions
- Abdominal pain (variable — may be masked by epidural)
Induction / Augmentation Risk Modifiers
- Oxytocin: modestly increased rupture risk (~1–1.5%)
- Misoprostol (PGE1): contraindicated in TOLAC — significantly increases rupture risk (2–6×)
- Dinoprostone (PGE2): use with caution; some guidelines advise avoidance
- Mechanical cervical ripening (Foley balloon): generally considered safer than prostaglandins
VBAC vs. Elective Repeat Cesarean (ERCS) — Comparative Risks
| Outcome | Successful VBAC | Failed TOLAC | ERCS |
|---|---|---|---|
| Maternal mortality | Lowest | Higher | Intermediate |
| Uterine rupture | 0.5–0.9% | Included above | ~0.02% |
| Transfusion | Low | Higher | Intermediate |
| Hysterectomy | Low | Higher | Low |
| Neonatal respiratory morbidity | Low (benefit) | — | Higher (transient tachypnea) |
| NICU admission | Low | Higher | Intermediate |
| Perinatal death (attributable) | Very low | ~0.1% | Very low |
| Future pregnancy placenta accreta spectrum | Lowest | — | Increases with each cesarean |
Intrapartum Management
Requirements for TOLAC (ACOG / RCOG)
- Setting: Facility capable of emergency cesarean within 30 minutes ("immediately available" surgical team)
- Continuous electronic fetal monitoring throughout labor
- IV access established
- Informed consent documenting VBAC and ERCS risks
- Blood type and screen (crossmatch if high risk)
- Anesthesia availability
Monitoring Points
- Closely monitor for rupture signs (above)
- Epidural analgesia is not contraindicated — does not mask rupture signs reliably, but is safe and does not reduce VBAC success
- No need to routinely palpate the uterine scar (not predictive)
If Rupture is Suspected
- Immediate laparotomy
- Neonatal resuscitation team at delivery
- Repair vs. hysterectomy depending on extent
Special Situations
Two Prior Cesareans
- ACOG (2019) states TOLAC is not contraindicated with 2 prior low transverse incisions if no other contraindications
- Success rate ~70%; rupture risk ~1.5–3.6%
- Requires thorough counseling
Twin Gestation
- TOLAC with twins is acceptable in selected patients (per ACOG); success rates ~70–75%
Macrosomia
- Estimated fetal weight > 4,000–4,500 g — relative contraindication; lower success and increased rupture risk
Gestational Age > 40 Weeks
- Success rates decline; induction increases risk further — individualize
Unknown Scar Type
- If operative report unavailable and no clinical suspicion of classic incision, low transverse is assumed — TOLAC may be offered with counseling
Counseling Framework
Patients should be counseled on:
- Probability of VBAC success (use prediction tools / individual factors)
- Risk of uterine rupture and its consequences (fetal death, hysterectomy)
- Benefits of vaginal delivery (faster recovery, lower morbidity in subsequent pregnancies)
- Risks of ERCS (surgical complications, placenta accreta spectrum in future pregnancies)
- Facility requirements — delivery must occur at an appropriately equipped hospital
ACOG recommends that VBAC be offered as a reasonable option to most women with one prior low transverse cesarean, and that the decision should be individualized through shared decision-making.
Key References: ACOG Practice Bulletin No. 205 (2019) — Vaginal Birth After Cesarean Delivery; RCOG Green-top Guideline No. 45 — Birth After Previous Caesarean Birth.
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