7.6 TOLAC, VBAC & Uterine Rupture
Key Takeaways
- Uterine rupture risk is 0.5 to 0.9 percent with one prior low transverse cesarean and 4 to 9 percent or higher with a prior classical or T-shaped incision, which is an absolute contraindication to trial of labor.
- An acute abnormal fetal heart rate pattern is the earliest and most sensitive sign of uterine rupture, present in more than 70 percent of cases.
- Sudden loss of fetal station, with a previously engaged head retracting to a high floating position, is a hallmark of uterine rupture.
- Prostaglandins are absolutely prohibited for cervical ripening in a scarred uterus, and the transcervical Foley catheter is the ripening method of choice.
- Epidural analgesia is safe and encouraged in trial of labor after cesarean because it does not mask rupture, which presents first with fetal heart rate change and with pain that breaks through the block.
Trial of Labor After Cesarean (TOLAC) & VBAC Management
Trial of labor after cesarean (TOLAC) refers to a planned attempt to labor by a woman who has previously given birth via cesarean delivery, with the goal of achieving a vaginal birth after cesarean (VBAC).
Candidate Eligibility Criteria (ACOG Guidelines)
- One or Two Prior Low Transverse Cesarean Deliveries: Documented transverse incision in the lower uterine segment.
- Clinically Adequate Maternal Pelvis: Clinically evaluated as adequate for the estimated fetal size.
- No Prior Uterine Scars: No history of classical, vertical, T-shaped, or inverted-T hysterotomy incisions, and no history of prior uterine rupture or extensive transmural myomectomy entering the uterine cavity.
- Immediate Surgical Capability: Labor must take place in a facility equipped for emergency cesarean delivery with immediate availability of anesthesia, surgical personnel, and neonatal resuscitation throughout active labor.
Predictors of VBAC Success
Overall, 60% to 80% of women who undergo TOLAC achieve successful vaginal delivery.
- Strongest Positive Predictor: A prior successful vaginal delivery (especially a prior successful VBAC). Women with a prior vaginal birth have an > 85% to 90% VBAC success rate and a significantly lower incidence of uterine rupture.
- Other Favorable Factors: Spontaneous labor onset, prior cesarean performed for a non-recurring indication (e.g., breech presentation, herpes lesion, fetal heart rate abnormality), maternal age < 35, normal BMI, and spontaneous cervical dilation upon admission.
- Unfavorable Predictors: Recurring indication for prior cesarean (arrest of dilation or arrest of descent), labor induction or augmentation, maternal obesity (BMI ≥ 30), advanced maternal age, gestational age > 40 weeks, fetal macrosomia (> 4,000 g), and short inter-pregnancy interval (< 18 months from prior cesarean to next conception).
Uterine Rupture Risks by Incision Type
| Previous Uterine Incision Type | Risk of Uterine Rupture during Labor | TOLAC Eligibility |
|---|---|---|
| One Prior Low Transverse Cesarean (LTCS) | 0.5% to 0.9% (~1 in 100 to 200) | Eligible Candidate |
| Two Prior Low Transverse Cesareans | 0.9% to 1.8% | Eligible Candidate |
| Prior Low Vertical Incision | 1.0% to 2.0% | Candidate only if scar did not extend into fundus |
| Prior Classical (High Vertical) Incision | 4.0% to 9.0%+ | STRICTLY CONTRAINDICATED (Repeat Cesarean at 36–37w) |
| Prior T-Shaped or Inverted-T Incision | 4.0% to 9.0%+ | STRICTLY CONTRAINDICATED |
| Prior Documented Uterine Rupture | 5.0% to 32.0% | STRICTLY CONTRAINDICATED |
Uterine Rupture: Pathophysiology, Clinical Presentation & Intrapartum Care
Uterine rupture is an acute tearing separation of all myometrial layers, including the overlying visceral peritoneum (complete rupture), often resulting in extrusion of the fetus, placenta, or umbilical cord into the maternal peritoneal cavity.
Clinical Presentation & Hallmark Signs
- Acute Abnormal Fetal Heart Rate Pattern: The earliest, most consistent, and most sensitive sign of uterine rupture, present in > 70% of cases. Typically manifests as sudden, profound, persistent bradycardia, recurrent late decelerations, or deep prolonged decelerations.
- Acute, Constant, Severe Abdominal Pain: Sharp, tearing lower abdominal pain that persists between contractions and often "breaks through" an otherwise fully functioning epidural analgesia block.
- Sudden Loss of Fetal Station: The fetal presenting part that was previously engaged (+1 or +2 station) retracts upward and floats away (–2 or –3 station) on digital examination as the fetus is extruded through the hysterotomy tear into the abdominal cavity.
- Cessation of Uterine Contractions: Contractions abruptly stop, or the baseline intrauterine resting tone suddenly drops on the intrauterine pressure catheter (IUPC).
- Maternal Hemodynamic Collapse: Tachycardia, hypotension, cool clammy extremities, syncope, and maternal hypovolemic shock secondary to massive intra-abdominal hemorrhage.
- Vaginal Bleeding & Hematuria: Frank vaginal bleeding may be present (though bleeding is predominantly internal/intra-abdominal); gross hematuria may occur if the rupture extends into the bladder base.
Intrapartum TOLAC Management Guidelines
- Continuous Electronic Fetal Monitoring (EFM): Continuous cardiotocography is mandatory from the onset of labor. Intermittent auscultation is unsafe in TOLAC.
- Vascular Access & Blood Banking: Establish functioning large-bore intravenous access (16- or 18-gauge) on admission; draw type and antibody screen; confirm blood bank availability.
- Cervical Ripening in TOLAC:
- Mechanical Ripening is Safe: Transcervical Foley bulb catheter (30 to 60 mL) is the ripening modality of choice. It achieves cervical change mechanically without increasing the risk of uterine rupture.
- PROSTAGLANDINS ARE ABSOLUTELY CONTRAINDICATED: Both misoprostol (PGE1) and dinoprostone (PGE2) are strictly prohibited for cervical ripening in TOLAC due to a 5- to 10-fold increase in uterine rupture rates.
- Oxytocin Usage: Oxytocin may be used for induction or augmentation of labor in TOLAC candidates with careful titration, but requires extreme vigilance. Avoid excessive doses and prevent uterine tachysystole, as high doses are associated with an increased rupture risk (up to 1% to 2%).
- Epidural Analgesia: Epidural analgesia is safe, appropriate, and encouraged in TOLAC. It does not mask the signs of uterine rupture (abnormal FHR patterns occur first, and severe peritoneal pain typically breaks through regional neuraxial blockade).
A 31-year-old G2P1 at 39 weeks gestation with one prior low transverse cesarean delivery is undergoing a trial of labor after cesarean (TOLAC). She has received epidural analgesia and is currently in active labor at 8 cm dilation with the fetal vertex at +1 station. Suddenly, the fetal heart rate drops from 140 bpm to 60 bpm and remains at this rate for 4 minutes. The patient reports acute, sharp lower abdominal pain that persists between contractions, and on repeat digital examination, the fetal vertex is now high and floating at –3 station. What is the definitive diagnosis and primary clinical action?
A 29-year-old G2P1 at 40 weeks gestation with one prior low transverse cesarean delivery presents desiring a trial of labor after cesarean (TOLAC). On examination, her cervix is 1 cm dilated, 20% effaced, firm, and posterior, with an unfavorable Bishop score of 2. Which method of cervical ripening is clinically indicated and safe for this patient?