Chapter 23: Trial of Labor After Previous Cesarean Section

INTRODUCTION

Trial of labor after cesarean delivery (TOLAC) refers to a planned attempt for a vaginal delivery by someone who has had a previous cesarean delivery, with the goal of having a successful vaginal birth after cesarean delivery (VBAC).

VBAC was first reported in 1923. Between 1970 and 2016, cesarean section rates in the United States increased from 5 to 31.9 percent due to several practice changes including the use of electronic fetal monitoring (EFM) and decreased operative and breech vaginal deliveries. TOLAC was reconsidered in the 1970s and supported as a reasonable approach in select pregnancies, which increased VBAC rates from approximately 5 percent in 1985 to 28.3 percent by 1996.

TOLAC should be considered for all women with one previous cesarean section presenting for prenatal care, provided there are no contraindications to TOLAC. In particular, women who are planning more than two children may be more motivated to consider TOLAC after their first cesarean due to the increased maternal risks associated with having three or more cesarean sections. Care providers and their patients should discuss the risks and benefits of both TOLAC and elective repeat cesarean section (ERCS) in a shared decision-making process while planning the birth. This discussion should be well documented in the prenatal record. TOLAC may be contraindicated in some situations and in those cases, a repeat cesarean section would be advised.

SUCCESS RATE

The success rate of TOLAC ranges from 50 to 85 percent. Factors that increase the likelihood of a VBAC include:

1. Previous vaginal birth and/or previous VBAC

2. Nonrecurring indication for the previous cesarean section such as malpresentation

3. Spontaneous labor

4. Favourable cervix on admission to the birthing unit (cervical dilation ≥4 cm)

5. No history of dystocia

6. Epidural use

7. Birthweight less than 4000 g

Although some factors decrease the likelihood of a VBAC, TOLAC may still be considered. However, these patients should be informed that they have a lower chance of VBAC and an increased risk of requiring a cesarean section and other complications. Factors that decrease the likelihood of a VBAC:

1. Increasing maternal age

2. High maternal BMI (>30 kg/m²)

3. Previous dystocia

4. Induction of labor

5. Delivery more than 40 weeks’ gestation

6. Birthweight more than 4000 g

Decision aids and prediction models for TOLAC success have been developed and can be used in antenatal counselling and shared decision-making. Prediction models have high predictive values for predicting VBAC but are poorer at predicting unsuccessful TOLAC.

PREREQUISITES FOR TOLAC

1. Patient understands and accepts the risks

2. Undertaken in an institution capable of performing an emergency cesarean section

Although it is ideal to have in-house obstetrics, anaesthesia, and surgical staff to optimize timely access to surgical management, this may not be a possibility in all birthing units. However, immediate mobilization of a ...