No randomized trials comparing outcomes in VBAC vs. repeat c/s as of 1999. However, "benefits of VBAC outweight the risks in most women with a prior low-transverse cesarean delivery (ACOG 1999)

I. Risks of "trial of labor" for VBAC:

  1. Uterine Rupture
    1. Presents with non-reassuring fetal heart rate and sometimes uterine or abdominal pain, loss of station of presenting part, vaginal bleeding, or hypovolemia
    2. May reseult in maternal and fetal death
    3. Meta-analyses of published trials confirm that pts with prior cesarian (or uterine incisions of any kind) have a higher risk of uterine rupture in labor than other women (e.g. 0.47% vs. 0.026%; See Evid. Rep. TEchnol. Assess 191:1, 2010-AFP)
    4. Risk ass'd with particular types of uterine incision
      1. "Classical" uterine scar: 4-9%
      2. T-shaped incision: 4-9%
      3. Low vertical incision: 1-7%
      4. Low transverse incision: 0.2-1.5%
      5. Past ruptured lower segment incision: 6%
      6. Past ruptured upper segment incision: 32%
    5. Prospective trial of 6137 women with h/o one prev. c/s and no contraindications to trial of labor. Mat. morbidity 8.1%; 1.3% had major complications (hysterectomy, ut. rupture, "operative injury"). Among women who had trial of labor vs. elective c/s, similar overall complication rates but twice the rate of major complications (hysterectomy, uterine rupture, or operative injury; 1.6% vs. 0.8%; incl. 10 vs 1 uterine ruptures). 60% of the 3249 women who had a trial of labor had successful vaginal deliveries. No deaths and no diff. in neonatal outcomes. (NEJM 335:689, 1996-JW)
    6. In a retrospective study of 20,095 deliveries of second infants in women with prior h/o c/s, incidence of uterine rupture was as follows for different groups (NEJM 345:3, 2001--JW)
      1. Repeat c/s: .16%
      2. Spontaneous labor: .52%
      3. Induction w/o prostaglandins: .77%
      4. Induction with prostaglandins: 2.45%
    7. In a prospective study of 162 women, the size of scar defects on transvaginal ultrasound done 6-9mos after cesarian delivery, there was a nonsig. association between larger scar defects and risk of rupture or dehiscence with subsequent deliveries (Obs. Gyn. 117:525, 2011-JW)
    8. In a systematic review of 21 studies of risk of uterine rupture during trial of labor for VBAC, overall excess risk of uterine rupture and perinatal infant death, compared with elective repeat cesarian, was 2.7/1000 births and 1.4/10,000 births, respectively (BMJ 329:19, 2004--JW)
  2. Overall risks
    1. In a prospective study of 17,898 women with singleton gestations and prior cesarean deliveries attempting vaginal delivery, overall success rate was 73.4% and overall incidence of uterine rupture was 0.7%. Risk for stillbirth, neonatal death, or hypoxic-ischemic encephalopathy was sig. higher w/trials of labor than with elective cesarean (0.38% vs. 0.13%), as were risks for maternal complications (5.5% vs. 3.6%) (NEJM 351:2581, 2004--JW)
  1. Those who end up having cesarian have increased risk of maternal and neonatal infection than women who have elective repeat c/s
  2. Risk of perinatal death (though < 1%) with VBAC is more likely than with elective repeat cesarian (AFP 70:1397, 2004)

II. Benefits of trial of labor for VBAC:

  1. When successful, ass'd with fewer blood transfusions, fewer postpartum infections, and shorter hospital stays

III. Success rates

  1. In published case series, 60-80% of pts attempting VBAC were able to deliver vaginally
  2. Success rate is higher among women who:
    1. Have had a successful vaginal delivery before or after her previous c/s
    2. Are at < 40wks gestation
    3. Have spontaneous rather than induced or augmented labor
    4. Are < 40yo
    5. Have favorable cervical exam findings
    6. Have estimated birth weight < 4kg
  3. In a cohort study of 2,000 women with h/o prior c/s undergoing a trial of labor, the incidence of repeat c/s was as follows (Obs. Gyn. 95:913, 2000--AFP):

IV. Criteria for candidacy for VBAC per ACOG 2004:

  1. No more than 2 prior cesarian sections (must both have been with low-transverse incisions)--note, per ACOG if has had 2, then only those pts with a previous vaginal delivery should be considered for trial of labor
  2. , No other uterine scars or previous rupture
  3. "Clinically adequate" pelvis
  4. Physician capable of monitoring labor & performing emergent c/s "immediately available throughout active labor"
  5. Personnel & anesthesia available for emergent c/s

V. Contraindications for VBAC per ACOG 2004:

  1. Prior classical or T-shaped c/s incision or other transfundal uterine surgery
  2. Contracted pelvis
  3. "Medical or obstetric complication that precludes vaginal delivery"

VI. Management of "trial of labor" for VBAC, per ACOG 1999:

  1. External cephalic version for breech presentation is not contraindicated
  2. Epidural anesthesia is not contraindicated
  3. Continuous electronic fetal monitoring
  4. "Persons who are familiar with the potential complications of VBAC should be present to watch for nonreassuring FHR patterns and inadequate progress in labor"
  5. No specific guidelines re: use of oxytocin, but implies that high rates of oxytocin infusion may increase risk of uterine rupture
  6. "The need to explore the uterus after successful vaginal delivery [for asymptomatic dehiscence of the uterine scar] is controversial"
  7. Prostaglandin-derived cervical ripening agents are associated with increased risk of uterine rupture during VBAC and ACOG (as of 2004) discourages their use in that setting.