A Trial of Labor (TOL) is a managed attempt for a person to deliver vaginally after a prior surgical birth. This decision is almost always discussed in the context of a previous Cesarean section, where the attempt is formally known as a Trial of Labor After Cesarean (TOLAC). TOLAC is an active effort to achieve a vaginal delivery under controlled supervision, contrasting with the alternative choice of a scheduled repeat Cesarean delivery. The process requires extensive counseling, a rigorous assessment of maternal and fetal health, and the hospital’s immediate readiness to perform emergency surgery.
Defining a Trial of Labor (TOLAC)
A Trial of Labor After Cesarean (TOLAC) is the planned attempt for a vaginal delivery by an individual who has previously given birth via Cesarean section. The objective is to achieve a Vaginal Birth After Cesarean (VBAC), which avoids the risks associated with major abdominal surgery and multiple subsequent Cesarean deliveries. This decision is typically made when the current pregnancy is healthy and the reasons for the previous surgical delivery are not expected to recur. The success rate for a TOLAC attempt ranges between 60% and 80% for well-selected candidates.
TOLAC differs from an Elective Repeat Cesarean Section (ERCS), which involves scheduling a surgical delivery before labor begins. The term TOLAC reflects the attempt itself, regardless of the outcome. A successful attempt results in a VBAC, while a failed attempt leads to a repeat surgical birth. The choice to attempt a TOLAC is a shared decision between the patient and the healthcare provider, requiring a detailed discussion of the risks and benefits of both options.
Essential Factors for Determining Candidacy
The selection of a good candidate for a TOLAC is governed by specific medical criteria that predict a high likelihood of a successful vaginal birth and a low risk of complications. The most important factor relates to the type of incision made in the uterus during the previous Cesarean delivery. A low transverse uterine incision, which involves a cut across the non-contractile lower segment of the uterus, is considered the ideal and safest type for a TOLAC attempt.
Individuals with a prior classical or T-shaped uterine incision are generally not candidates because these cuts involve the contractile upper part of the uterus, substantially increasing the risk of rupture during labor. Most guidelines recommend TOLAC for those with a single prior low transverse C-section, but it may be considered for some patients with two prior low transverse incisions. A history of a previous vaginal delivery, even before the Cesarean section, is one of the strongest positive predictors for a successful VBAC.
Maternal health factors also play a substantial role in determining candidacy. Conditions like a high maternal Body Mass Index (BMI) or advanced maternal age reduce the probability of success. The fetus must be in a favorable position, specifically head-down (vertex presentation), as other presentations complicate the attempt. Furthermore, an estimated fetal weight (EFW) above 4,000 grams (macrosomia) is associated with a lower success rate and may be a factor against attempting a TOLAC.
Institutional readiness is a requirement for a safe TOLAC attempt. The hospital must have the capability to perform an emergency Cesarean delivery within a short timeframe, typically within 30 minutes, to address urgent complications. This requires the immediate availability of an obstetrician, an anesthesiologist, and a surgical team on the labor and delivery unit. Without this immediate support, the risks of a TOLAC are considered too high.
The Process of Labor Monitoring and Management
Once a qualified candidate begins a trial of labor, the management protocol is distinct. Continuous electronic fetal monitoring (EFM) is mandatory throughout the active labor process. This close observation allows the care team to detect subtle changes in the baby’s heart rate pattern, which can be the earliest sign of a developing complication, such as uterine rupture.
Spontaneous onset of labor is generally preferred for a TOLAC because the induction or augmentation of labor carries an increased risk of uterine rupture. If labor assistance is necessary, the use of labor-inducing medications, particularly high-dose oxytocin, is carefully limited compared to a typical labor scenario. Certain medications used for cervical ripening are often avoided entirely due to their association with higher rupture rates in scarred uteri.
The labor progress is meticulously tracked to ensure it is advancing appropriately, and the care team remains vigilant for signs that the trial is failing. Criteria for converting the TOLAC to an emergency Cesarean section include signs of non-reassuring fetal status, such as prolonged fetal bradycardia, or a failure of the cervix to dilate or the baby to descend. These decision points are acted upon rapidly to ensure the best possible outcomes for both the parent and the baby.
Potential Outcomes and Associated Specific Risks
A TOLAC attempt has two potential outcomes: a successful VBAC or a failed trial resulting in a repeat Cesarean section. Achieving a VBAC is associated with decreased maternal morbidity, a quicker recovery time, and a lower risk of complications in future pregnancies compared to multiple Cesarean deliveries. However, a failed TOLAC that converts to an emergency C-section is associated with the highest overall risk of maternal and neonatal complications.
The most specific risk associated with attempting a TOLAC is uterine rupture, which occurs when the prior Cesarean scar tears open during labor contractions. The risk of this event is low, estimated to be less than 1%, typically cited in the range of 0.4% to 0.8% for well-selected candidates. If a rupture occurs, it can cause severe maternal hemorrhage and interrupt the oxygen supply to the baby, requiring an immediate emergency Cesarean delivery.
Uterine rupture necessitates rapid surgical intervention, often including a laparotomy to deliver the baby and repair the uterine tear. While the absolute risk of severe neonatal neurological injury remains low, it is slightly higher during a TOLAC than with a planned ERCS. The decision to pursue a TOLAC involves balancing the benefits of a successful vaginal birth against the serious risk of uterine rupture and the higher risks associated with a failed attempt.