A Trial of Labor After Cesarean (TOLAC) is a planned attempt to achieve a Vaginal Birth After Cesarean (VBAC). Medical induction, which uses medications or mechanical means to stimulate labor, introduces complexity to the TOLAC process. Combining induction with a TOLAC alters the risk profile compared to waiting for spontaneous labor. This combination requires careful patient selection and shared decision-making.
The primary concern associated with any TOLAC, especially an induced one, is uterine rupture. This is the complete separation of the uterine muscle wall, most often occurring at the site of the previous cesarean scar. This event can lead to severe maternal hemorrhage, fetal distress, and require an immediate emergency cesarean delivery and potentially a hysterectomy.
Inducing labor significantly increases the likelihood of this complication compared to a spontaneous TOLAC. The rate of uterine rupture for women experiencing spontaneous labor is low, around 0.4% to 0.7%. In the setting of induced labor, this risk increases substantially, with reported rates ranging from 1.4% up to 2.2%.
This elevated risk stems from the increased stress placed on the old scar site by chemically or mechanically stimulated contractions. Artificial stimulation may cause contractions to become stronger, more frequent, or less coordinated than those in spontaneous labor. The relative increase in risk is significant and must be carefully weighed when considering induction.
Strict Criteria for Induced TOLAC Eligibility
A patient must meet specific, rigorous criteria to be considered a candidate for an induced TOLAC. The most fundamental requirement relates to the type of incision used in the previous cesarean delivery. Only a prior low-transverse uterine incision is accepted, as this horizontal cut heals with the strongest scar.
A prior classical incision, a vertical cut in the upper uterine muscle, is an absolute contraindication for any TOLAC due to the high risk of rupture. Similarly, a history of prior uterine rupture or extensive transfundal uterine surgery excludes a patient. Patients with an unknown prior incision type may still be candidates if there is no clinical suspicion of a high-risk classical scar.
The number of previous cesarean deliveries is a major factor. Most guidelines focus on patients with only one prior low-transverse cesarean. Offering TOLAC after two prior cesareans nearly doubles the risk of uterine rupture, placing the patient in a higher-risk category. The original reason for the previous cesarean should ideally be a non-recurring indication, such as a fetal presentation issue.
The condition of the cervix at the time of induction is a significant predictor of success and safety. Clinicians use the Bishop Score to assess the favorability of the cervix for induction. A higher, more favorable Bishop Score indicates the cervix is soft, partially dilated, and thinned, making induction more likely to succeed. Conversely, a low Bishop Score is associated with a four-fold increase in the risk of uterine rupture during an induced TOLAC.
Permitted and Prohibited Induction Methods
The choice of induction method is important in patients attempting a TOLAC, as certain pharmacological agents are strictly avoided due to their effect on the scarred uterus. Prostaglandins, a class of drugs used for cervical ripening and labor induction, are generally prohibited. Specifically, Misoprostol (Cytotec) should not be used for third-trimester induction in a patient with a prior cesarean or major uterine surgery.
These medications cause intense and unpredictable uterine contractions, significantly increasing the risk of uterine rupture. Other prostaglandins, such as Dinoprostone, are also associated with increased rupture risk in a scarred uterus and are generally not recommended for TOLAC candidates.
Safer alternatives focus on mechanical methods, which gently dilate the cervix without the risk of uterine overstimulation. Mechanical dilators, such as a transcervical balloon catheter, are viable options even with an unfavorable Bishop Score. These devices are inserted and inflated, applying pressure to help the cervix open.
Once the cervix is favorable, the use of intravenous Oxytocin (Pitocin) may be considered. Oxytocin is administered to stimulate contractions, but it must be used with caution and at a low dose. Continuous fetal heart rate monitoring is necessary to watch for signs of fetal distress, which can indicate uterine rupture.
The preferred strategy for induced TOLAC is the sequential use of a mechanical method followed by low-dose Oxytocin. This balances the necessity of induction with minimizing the risk of scar separation.