Residency · Residency · Obstetrics Gynecology

Vaginal Birth After Cesarean (VBAC) and Trial of Labor

Overview

VBAC refers to successful vaginal delivery after a prior cesarean, while TOLAC refers to the trial of labor after cesarean, which is the process of attempting vaginal delivery. The VBAC rate in the United States is approximately 13 to 14% among eligible women. The overall TOLAC success rate ranges from 60 to 80%, varying by patient selection. VBAC avoids major abdominal surgery and reduces morbidity in both the current and future pregnancies.

Patient Selection and Counseling

Candidates for TOLAC

Appropriate candidates include women with one prior low transverse cesarean delivery, no contraindications to vaginal delivery, a clinically adequate pelvis, and access to appropriate institutional resources with the ability to perform emergent cesarean delivery.

Contraindications to TOLAC

TOLAC is contraindicated in women with a prior classical (vertical) or T-shaped uterine incision, prior uterine rupture, active contraindications to labor (placenta previa, vasa previa, or malpresentation), and prior full-thickness myomectomy with entry into the uterine cavity (relative, with institution-dependent practice).

Factors Favoring Success

Prior vaginal delivery is the strongest predictor of TOLAC success, with success rates exceeding 85 to 90%. Other favorable factors include prior VBAC, spontaneous labor onset (as opposed to induction), a favorable cervical exam (higher Bishop score), a non-recurrent indication for the prior cesarean (such as breech or previa rather than arrest disorder), maternal age below 35, BMI below 30, interpregnancy interval greater than 18 months, and estimated birth weight below 4,000 g.

Factors Associated with Lower Success / Higher Rupture Risk

A prior cesarean for arrest disorder is associated with lower success (approximately 50 to 60%). Other unfavorable factors include induction of labor, no prior vaginal delivery, obesity (BMI above 30), gestational age beyond 40 weeks, a short interpregnancy interval (less than 18 months, which also increases rupture risk), and an increasing number of prior cesareans.

VBAC Calculator (MFMU Network)

The Maternal-Fetal Medicine Units Network provides entry-to-care and admission prediction models that estimate the likelihood of successful VBAC based on maternal characteristics. The calculator is available online and serves as a useful counseling tool, but it should not be the sole basis for decision-making. Some concerns have been raised about racial bias, as race was included as a variable in the original model.

<image>Counseling framework diagram for TOLAC showing success factors on one side (prior vaginal delivery, spontaneous labor, favorable cervix, non-recurrent indication) and risk factors on the other (arrest disorder indication, induction, obesity, no prior vaginal delivery), with overall success rates for each combination</image>

Risks and Benefits

Benefits of Successful VBAC (vs. Repeat Cesarean)

Successful VBAC offers shorter recovery time, lower infection rates, less blood loss, avoidance of major abdominal surgery, lower risk of placenta previa and accreta in future pregnancies, lower VTE risk, and potential psychological and emotional benefits.

Risks of TOLAC

The most serious risk is uterine rupture, which occurs in 0.5 to 0.7% of women with one prior low transverse cesarean. This is a catastrophic event involving fetal extrusion into the peritoneal cavity and massive hemorrhage. Fetal mortality with complete rupture is 5 to 10%, and maternal hysterectomy is required in 14 to 33% of rupture cases. Failed TOLAC requiring emergency cesarean carries higher morbidity than a planned repeat cesarean, with increased infection, hemorrhage, and transfusion rates, as well as higher neonatal morbidity compared to either successful VBAC or planned cesarean. Uterine dehiscence, an incomplete separation with an intact serosal layer, is less catastrophic than true rupture and may be found incidentally at repeat cesarean.

Risks of Repeat Cesarean (Especially Multiple)

Repeat cesarean carries increasing surgical complications with each subsequent procedure, including adhesions and risks of bladder and bowel injury. The risk of placenta previa and accreta increases exponentially with each additional cesarean. Operative times and recovery periods are longer.

Two or More Prior Cesareans

TOLAC with two prior cesareans has a success rate of 60 to 75% in selected patients. The uterine rupture risk is slightly higher, at approximately 0.9 to 1.8%. ACOG does not contraindicate TOLAC with two prior cesareans but emphasizes careful counseling. Patient selection is critical, and prior vaginal delivery remains the strongest positive predictor.

Intrapartum Management

Institutional Requirements

The institution must have the capability to perform emergent cesarean delivery. ACOG recommends "immediately available" personnel, including the surgeon, anesthesiologist, nursing staff, and operating room, though this language has limited TOLAC access at smaller hospitals. ACOG acknowledges that institutions may develop their own risk-management protocols. Continuous electronic fetal monitoring is mandatory. IV access is established and a type and screen is obtained on admission.

Labor Augmentation and Induction

Spontaneous labor has the highest success rate and is preferred. Oxytocin augmentation is acceptable but should be titrated carefully. There is no clear evidence that oxytocin increases rupture risk beyond the baseline TOLAC risk, though high doses may. For cervical ripening, the Foley catheter is acceptable. Misoprostol is contraindicated because it significantly increases uterine rupture risk to 2 to 5%. Dinoprostone is generally avoided, though some institutions allow it with caution. Induction with an unfavorable cervix has the lowest success rate in TOLAC.

Recognizing Uterine Rupture

Signs of uterine rupture include sudden, severe abdominal pain (which may occur between contractions), fetal heart rate abnormalities (prolonged decelerations and bradycardia, which are the most common and most reliable sign), loss of fetal station (recession of the presenting part), cessation of contractions, vaginal bleeding (which may be absent if hemorrhage is intraperitoneal), and maternal tachycardia and hypotension (late signs). Management involves emergent cesarean delivery with decision-to-delivery as fast as possible, laparotomy with assessment of the rupture site, repair of the uterine defect if possible or hysterectomy if irreparable, massive transfusion protocol activation if needed, and presence of the neonatal resuscitation team.

<image>Intraoperative illustration comparing uterine dehiscence (thinning and separation of the scar with intact serosa and minimal bleeding) versus complete uterine rupture (full-thickness defect with fetal parts visible through the defect and significant hemorrhage)</image>

After Successful VBAC

After successful VBAC, the cervix and vagina are inspected for lacerations, and routine postpartum care is provided. Uterine exploration is not needed unless clinical concern exists. The subsequent VBAC success rate is very high, exceeding 90%. Each successful VBAC further improves the safety profile of subsequent TOLAC.

After Failed TOLAC

Failed TOLAC results in cesarean delivery with standard technique. Operative findings (uterine scar integrity and adhesions) are documented. The complication rate is higher than elective repeat cesarean, though most failed TOLACs are straightforward. Counseling regarding future delivery options is provided, and emotional support is important because failed TOLAC can be psychologically difficult.

Special Situations

VBAC with Unknown Uterine Scar Type

When the operative report is unavailable and clinical history suggests a low transverse incision (term delivery with a low transverse skin incision), TOLAC may be offered. If a classical incision cannot be excluded, repeat cesarean is recommended.

External Cephalic Version with Prior Cesarean

External cephalic version is not contraindicated in women with a prior cesarean. Success rates are similar to patients without prior cesarean.

Twin Gestation with Prior Cesarean

Data are limited, but TOLAC may be considered in selected cases with a presenting vertex twin and one prior low transverse cesarean. Individualized counseling is required.

Clinical Pearls

Prior vaginal delivery is the single strongest predictor of TOLAC success. It virtually doubles the success rate.

Misoprostol is absolutely contraindicated in TOLAC patients due to unacceptably high uterine rupture risk.

Fetal bradycardia or prolonged decelerations are the most common and earliest sign of uterine rupture.

Failed TOLAC carries more morbidity than either successful VBAC or planned repeat cesarean. Proper patient selection is critical.

Each additional cesarean increases the risk of placenta accreta spectrum exponentially. This long-term consequence should be included in counseling.

The "immediately available" surgical capability requirement has limited TOLAC access in rural and community settings. ACOG acknowledges institutional flexibility in interpreting this requirement.

TOLAC with two prior cesareans is not contraindicated but requires careful selection and counseling.

References

• ACOG Practice Bulletin No. 205: Vaginal Birth After Cesarean Delivery (2019)
• Landon MB et al. Maternal and perinatal outcomes associated with a trial of labor after prior cesarean delivery (MFMU Cesarean Registry). N Engl J Med. 2004;351:2581-2589
• Grobman WA et al. Development of a nomogram for prediction of VBAC. Obstet Gynecol. 2007;109:806-812
• ACOG/SMFM Obstetric Care Consensus No. 1: Safe Prevention of the Primary Cesarean Delivery (2014)
• Macones GA et al. Predicting outcomes of trials of labor in women attempting VBAC. Am J Obstet Gynecol. 2005
• Tahseen S, Griffiths M. Vaginal birth after two caesarean sections: a systematic review. BJOG. 2010;117:5-19

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