Predictors and Considerations for Vaginal Birth After Cesarean Section

Key Predictors of VBAC Success

The American Academy of Family Physicians notes that having had a previous vaginal birth is the single most important predictor of successful vaginal birth after cesarean section (VBAC) 1, 2
About 74% of U.S. women who attempt labor after cesarean (LAC) have a successful vaginal birth 1

Higher Bishop scores and more progression in labor at admission increase the likelihood of successful VBAC 1
The likelihood of successful VBAC decreases when labor is induced using oxytocin 1
The likelihood of successful VBAC also decreases when the estimated fetal weight is ≥4,000g (8 lb, 13 oz) 1

Labor induction carries varying risks of uterine rupture depending on the method used, with oxytocin carrying a 1.1% risk (95% CI, 0.9% to 1.5%) 3
Prostaglandin E2 carries a 2% risk (95% CI, 1.1% to 3.5%) of uterine rupture 3
Misoprostol should not be used for cervical preparation or induction of labor in women with a previous cesarean delivery, as it carries a significant risk of uterine rupture 1, 4
While short-term maternal outcomes are as good or better with VBAC compared to repeat cesarean delivery, perinatal mortality is slightly higher 1, 5

For most women who have had one or two cesarean deliveries, attempting VBAC is practical and safe 1
Physicians should discuss the possibility of VBAC early in prenatal care, considering each patient's risk factors 1
Physicians should reevaluate the labor plan when patients present in labor, considering factors that may affect the chance of delivering vaginally 1

Failing to recognize the significance of previous vaginal delivery as the strongest predictor of VBAC success 1, 2
Using misoprostol for cervical ripening or induction in women with previous cesarean delivery 1, 4

Misoprostol should not be used for cervical ripening or labor induction in women attempting VBAC because it is associated with a uterine rupture risk of approximately 13 %【6】.
Prostaglandin E₂ is also contraindicated for induction in VBAC candidates, carrying a uterine rupture risk of about 2 %【6】.
Oxytocin may be used for labor augmentation during VBAC only with careful titration and continuous fetal monitoring, as it is linked to a uterine rupture risk of roughly 1.1 %【6】.

Facilities offering VBAC must be equipped to perform an emergency cesarean delivery within 30 minutes of decision to intervene【6】.
In the event of suspected uterine rupture, surgical intervention (laparotomy) should be initiated within 18 minutes to optimize maternal outcomes【6】.

Successful VBAC is associated with a lower maternal mortality rate compared with elective repeat cesarean delivery【6】.
Perinatal mortality is modestly higher for trial of labor after cesarean (TOLAC) than for scheduled repeat cesarean delivery【6】.
Short‑term maternal morbidity after VBAC is comparable to or better than after repeat cesarean, with reduced infection rates, decreased blood loss, and shorter hospital stays【6】.

Misoprostol should never be used for cervical preparation or induction of labor in women with a prior cesarean delivery during the third trimester, due to a uterine rupture risk of approximately 13 % in this population. 7
Prostaglandin E₂ (dinoprostone) carries a uterine rupture risk of about 2 % (95 % CI 1.1 %–3.5 %) in women with a previous cesarean, with at least one documented rupture in comparative studies. 7

A Foley catheter balloon is the safest mechanical cervical ripening option for TOLAC patients, with no reported uterine ruptures in the cited evidence. 7
When mechanical methods are exhausted and induction is medically necessary, low‑dose oxytocin may be used, but it still carries a rupture risk of 1.1 % (95 % CI 0.9 %–1.5 %) and reduces the likelihood of successful VBAC compared with spontaneous labor. 7

First‑line cervical ripening for TOLAC should be a Foley catheter (no reported ruptures). 7
If induction remains necessary after mechanical methods fail, oxytocin can be considered with continuous monitoring. 7
Misoprostol (13 % rupture risk) and prostaglandin E₂ (2 % rupture risk) must be avoided. 7

An inter‑delivery interval shorter than 18 months significantly increases uterine rupture risk. 7
A classic (vertical) uterine scar is an absolute contraindication to TOLAC regardless of ripening method. 7
Estimated fetal weight of ≥ 4000 g lowers the probability of successful VBAC. 7

Short‑term maternal outcomes are comparable or better with a successful VBAC versus a repeat cesarean delivery. [7][8]
Perinatal mortality is higher with TOLAC compared with a scheduled repeat cesarean delivery. [7][8]
A prior vaginal delivery is the strongest predictor of VBAC success, with an overall success rate of roughly 74 %. 8