VBAC: When is it safe?
When do risks outweigh benefits, in light of ACOG’s newly cautious advisory? What conditions call for extra concern?
The use of prostaglandins in labor induction greatly increases the risk of rupture, with rates of 24.5 per 1,000 reported, compared with 5.2 per 1,000 in women with spontaneous labor.26 ACOG strongly discourages the use of prostaglandin cervical ripening agents in labor inductions.26
Seek out other factors
Women who initially appear eligible may harbor other characteristics or conditions that warrant special attention.15,26-28
External cephalic version. Although 1 study29 concluded it is effective in women undergoing a trial of labor after cesarean, vigilance is recommended.
Twin gestations. Two retrospective studies involving a total of 45 women found VBAC to be safe in twin gestations. Because of the limited number of women studied and the lack of randomized, controlled trials, caution is strongly advised.30,31
Macrosomia. The rate of uterine rupture rises in women who have not had a previous vaginal delivery.27
Postdates. Although VBAC is less likely to succeed after 40 weeks’ gestation, the risk of uterine rupture increases only with induction of labor.11
Analgesia. Women undergoing a trial of labor can receive epidural anesthesia without increasing the risk of rupture or failed VBAC and without obscuring the signs and symptoms of uterine rupture.32,33 In fact, as ACOG notes, effective pain relief may encourage more women to try VBAC.1
Previous vaginal delivery. Women who have delivered vaginally are more likely to succeed at VBAC—by a factor of 9 to 28—than those who have not.34,35
Other conditions such as maternal obesity and advanced age should be evaluated in light of the patient’s overall risk-benefit profile. Although caution is recommended, definitive data are lacking.
TABLE
Criteria for trial of labor
| QUALIFICATIONS |
| 1 prior low-transverse cesarean section |
| Clinically adequate pelvis |
| No other uterine scars |
| DISQUALIFICATIONS |
| Prior classical or T-shaped uterine incision |
| Multiple uterine incisions |
| Previous uterine rupture |
| Contracted pelvis |
| Contraindications to vaginal birth |
| REQUIREMENTS THROUGHOUT ACTIVE LABOR |
| Obstetrician immediately available |
| Continuous electronic monitoring of the fetal heart rate |
| Personnel skilled in interpreting fetal tracings |
| Anesthesia for emergency cesarean |
| Physician qualified for emergency cesarean |
| PRECAUTIONS |
| Unknown uterine scars |
| Prior low vertical uterine incision |
| Uterine malformations |
| Prior single-layer uterine closure |
| Short interdelivery interval |
| Need for labor induction |
| Need for external cephalic version |
| Twin gestation |
| Suspected macrosomia |
| Maternal obesity |
| Postdates |
| Advanced maternal age |
| No prior vaginal delivery |
| Source: ACOG1 |
Prognostic formulas
One decision analysis36 concluded that VBAC is a reasonable option when the chance of success exceeds 50% and the desire for future pregnancy is 10% to 20% or more. Although scoring systems have been proposed to predict the likelihood of success, individualized assessment of each patient is ideal. (See “Case by case: Adding up the decisive factors”.)
CASE 1
A single cesarean and a healthy fetus
After her obstetrician encourages a repeat cesarean at 39 weeks’ gestation, a 39-year-old gravida seeks a second opinion. Her obstetric history includes a remote first-trimester miscarriage and a cesarean section, 2 years prior, of vertex-vertex twins at 36 weeks for arrest of labor at 8 cm. Tubal ligation is planned after delivery.
The previous operative report indicates that a low-transverse uterine incision was repaired in 2 layers. The patient plans to deliver at a local community hospital without full-time, in-hospital anesthesiology services.
This pregnancy has been uncomplicated, and ultrasound has confirmed a normally grown fetus in vertex presentation with a fundal placenta. The patient is considering vaginal birth after cesarean (VBAC).
Decision Multiple factors make VBAC unwise
This patient is a poor candidate due to advanced maternal age, no prior vaginal birth, and the previous cesarean for failure to progress. Lack of round-the-clock anesthesiology at her chosen hospital contraindicates trial of labor.1
Her request for postpartum sterilization also makes repeat cesarean wiser.
After these risks are explained, the patient accepts the recommendation for elective repeat cesarean.
CASE 2
Breech presentation, short interdelivery interval
A 28-year-old gravida has a breech presentation at 37 weeks. She has had 3 spontaneous vaginal deliveries and 1 cesarean section at term for a nonreassuring fetal tracing in labor. The cesarean was 14 months ago. The operative note is not available. She says she was told future vaginal deliveries would be possible.
She plans to have a large family.
Apart from the breech presentation, this pregnancy has been uneventful. The patient requests external cephalic version prior to a trial of labor.
Decision Take future plans into account
Placenta previa, accreta, adhesions, and intraoperative injuries are recognized risks in patients with a higher number of cesarean deliveries.
In this case, breech presentation, a short interdelivery interval, and an undocumented uterine incision warrant caution. Given that the patient’s cesarean section was performed at term in the United States, and that she was told she would be able to have a subsequent vaginal birth, she underwent a successful external cephalic version in the delivery room. She had an uneventful spontaneous vaginal delivery 3 weeks later.
CASE 3
Good candidate, nervous about risk
A 30-year-old woman with 1 uncomplicated vaginal delivery and 1 cesarean section 3 years prior presents in her third pregnancy for counseling about VBAC.
Her cesarean was performed through a transverse incision in the lower uterine segment for repetitive deep variable decelerations. A friend recently experienced uterine rupture during a trial of labor, resulting in a hysterectomy. She is undecided about future childbearing.
Decision Patient and physician agree on cesarean
With a prior vaginal delivery and a previous cesarean through a low-transverse uterine incision over 18 months ago for an indication that is unlikely to recur, the likelihood of VBAC success is high.
However, the patient was worried by potential risks for uterine rupture, adverse perinatal outcome, and loss of future reproductive potential. After considering the risks and benefits, she requested a repeat cesarean delivery.
After fully counseling the patient on the risks and benefits of VBAC versus elective repeat cesarean, a management plan was made and documented.
The patient underwent an uncomplicated cesarean section at 39 weeks and delivered a healthy baby.
