Chapter 23: Trial of Labor After Previous Cesarean Section

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.

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.

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 surgical team is necessary when risk factors or signs of uterine rupture are identified. The woman and her care provider must be aware of the availability of obstetrics, anesthesia, pediatrics, and operating room staff at the center where she chooses to deliver and the center must have a plan for managing obstetrical emergencies, including a uterine rupture.

1. Previous fundal, classical, inverted T, or low vertical uterine incision

2. Previous major uterine reconstruction (e.g., full-thickness repair for myomectomy, repair of Mullerian anomaly, cornual resection)

3. Previous uterine rupture

4. Unknown previous uterine incision

5. Advice against TOLAC after prior cesarean section

6. Any other obstetrical contraindications for vaginal delivery

7. Unavailable timely access to the operating room for emergency cesarean section

8. Patient requests ERCS and declines TOLAC

The benefits and risks of TOLAC versus ERCS must be presented to the patient. The balance of risks and the chances of VBAC must be acceptable to the patient. The overall risk of a TOLAC resulting in a VBAC are lower than the risks of surgery associated with an ERCS; however, TOLAC has the chance of resulting in an emergency cesarean section, and a chance of uterine rupture with their associated increase in maternal morbidity and mortality. Although the risk of maternal mortality, uterine rupture, and serious maternal morbidity is higher in TOLAC, the absolute risks of these outcomes are low. Similarly, the relative risk of perinatal morbidity and mortality and serious morbidity is higher for TOLAC compared to ERCS but the absolute risk is low.

Uterine Rupture

Uterine rupture is defined as a full thickness disruption of the myometrium and overlying serosa. Uterine “dehiscence” is an incomplete disruption (or uterine window) that does not include the serosa. The risk of uterine rupture with TOLAC and a history of one prior low transverse cesarean section is approximately 0.47 percent. Management of uterine rupture includes stabilizing hemodynamically unstable patients with fluids and blood transfusions as required and urgent cesarean delivery. The choice of a midline or Pfannenstiel incision will depend on the clinical scenario and provider preference. Repair of the uterine defect at the time of laparotomy after delivery may be possible but depends on the extent of the rupture, maternal hemodynamic stabilty, and the surgeon. Uterine rupture is associated with an increased risk of hysterectomy (14-33%), particularly if the rupture is lateral or very large. The overall risk of perinatal mortality related to uterine rupture is 6.2 percent, although reports range from 5 to 26 percent.

Factors That Increase the Risk of Uterine Rupture

• Previous uterine rupture

• Previous fundal, classical, inverted T, or low vertical uterine incision; previous myomectomy

• Induction of labor (IOL) with pharmacologic cervical ripening agents, for example, prostaglandins

• Oxytocin for IOL or augmentation

• Two or more previous cesarean sections

• Short interpregnancy interval, especially less than 18 months

• Thin lower uterine segment (although there is no agreed upon threshold value to use to predict the risk of uterine rupture)

• Longer second stage

A prior vaginal delivery either before or after the prior cesarean delivery significantly reduces the risk of uterine rupture with TOLAC but does not eliminate it.

I. Preadmission

1. The risks and benefits of TOLAC versus ERCS should be discussed prior to the onset of labor. The discussion is part of a shared decision-making process and should be documented in the patient chart

2. Patient should present to hospital immediately for:

   1. Suspected labor

   2. Suspected rupture of the membranes

   3. Vaginal bleeding

   4. Any other obstetrical concerns

II. Evaluation

1. Evaluation of maternal status:

   1. Physical examination

   2. Cervical assessment

   3. Initiation of intravenous line and infusion

   4. Bloodwork for complete blood count, type, and screen

2. Evaluation of fetal status:

   1. EFM

   2. Fetal presentation: vaginal examination and/or ultrasound

III. Intrapartum

1. Monitoring of fetal well-being: Continuous EFM is recommended because it is the best marker of uterine rupture. FHR tracing abnormalities, especially complicated variable or late decelerations, are the most commonly observed signs of uterine rupture and may present up to 1 hour prior to rupture

2. Monitoring of maternal well-being. Maternal mobility does not need to be restricted (telemetry can be used)

3. Intravenous access: Recommended in case of cesarean section or blood product administrations

4. Monitoring of labor progress: usual uterine contraction pattern does not change in TOLAC, and usual standards should be used to assess labor progress. Lack of progress in 2 to 3 hours in the presence of adequate contractions requires reassessment of the method of delivery

5. Epidural or other pain management as normally indicated. These are not expected to mask signs or symptoms of uterine rupture, because the most common sign of rupture is fetal heart tracing abnormalities

IV. Postpartum

Exploration of the uterine cavity is not routinely indicated unless there are concerning signs or symptoms

Delivery prior to the onset of spontaneous labor may be required for medical reasons in women with a previous cesarean section. IOL is not contraindicated for women wanting a TOLAC, but IOL has implications for the chance of a VBAC and the risk of uterine rupture.

1. Uterine rupture rates increase with IOL (0.7-2.7%). The highest risk is more than 40 weeks’ gestation (3.2%). Uterine rupture risks differ with the type of induction method used

2. With IOL, vaginal birth rates with TOLAC are lower and cesarean section rates are higher

3. Mechanical induction with a balloon (Foley) catheter is not contraindicated. It is associated with VBAC rates of 54 to 58 percent

4. Oxytocin is not contraindicated for either induction or augmentation. It is associated with an increased risk of uterine rupture (1.1%, approximately double that of baseline risk)

5. Women induced with either artificial rupture of membranes (ARM) or oxytocin with a favourable cervix have VBAC rates similar to spontaneous labor (74%)

6. Prostaglandin E₂ (dinoprostone) is not recommended. It is associated with increased risk of uterine rupture (2%)

7. Prostaglandin E_l (misoprostol) is contraindicated and is associated with a high risk of uterine rupture (6-19%)

Early recognition of uterine rupture and a facility that can provide rapid intervention are essential components of TOLAC. Failure of either of these may result in poor outcomes.

1. Abnormal fetal heart rate (most common sign)

2. Abdominal pain

3. Vaginal bleeding

4. Acute onset of scar pain or tenderness

5. Hematuria

6. Maternal tachycardia, hypotension, or hypovolemic shock

7. Palpation of fetal parts abdominally

8. Elevation of the presenting part unexpectedly (i.e., loss of station)

9. Chest pain, shoulder tip pain, and/or sudden shortness of breath

10. A change in uterine activity (decrease or increase) may occur but no consistent change has been identified

There is no single sign that reliably indicates a uterine rupture has occurred. FHR abnormalities (uncomplicated or complicated variable decelerations, late decelerations), persistent abdominal pain, and tachsystole may be an indicator of the initiation of uterine scar separation and frequently precede uterine rupture during TOLAC. When confronted with significant FHR abnormalities and a birth that is not imminent, a cesarean section should be considered to avoid a terminal bradycardia. The classic triad—abdominal pain, vaginal bleeding, and abnormal fetal heart rate—is seen only in 9 percent of the cases.

When a uterine rupture is suspected, an emergency cesarean section should be performed immediately in order to decrease maternal and neonatal morbidity and mortality. Maternal and fetal outcomes worsen as the interval between decision to delivery increases and every minute counts. Centers that offer TOLAC should have a plan for managing obstetrical emergencies, including urgent cesarean sections.

1. TOLAC success rates in patients with more than one previous cesarean are similar to women with only one previous cesarean section; however, they have a higher risk of uterine rupture (1.1-1.6%), blood transfusion, and hysterectomy

2. External cephalic version (ECV) is not contraindicated with previous cesarean section

3. Multiple gestation, diabetes, or fetal macrosomia are not contraindications for TOLAC

4. Interdelivery intervals do not appear to affect VBAC rates. However, the risk of uterine rupture increases with shorter interdelivery intervals. An interval of less than 18 months between deliveries is associated with an increased risk of uterine rupture for TOLAC. The best estimate of the uterine rupture rate for an interval of less than 12 months is 4.8 percent, while estimates of rates of rupture between 18 and 24 months and more than 24 months are 1.9 and 1.3 percent, respectively

5. Breech presentation is not an absolute contraindication for TOLAC; however, there is insufficient data to inform the discussion about possible additional risks

6. A single-layer locked uterine closure may increase the risk of uterine rupture with TOLAC compared to a double-layer closure of the uterus (3.1% vs. 0.5%)

7. Lower uterine thickness and uterine rupture are related; however, there is no clear cutoff for consideration of safe TOLAC. Routine ultrasound measurement of the lower uterine segment is not indicated for planning TOLAC

8. Previous operative reports should be obtained when possible to determine the type of prior uterine incision. If the information cannot be obtained but there is a high likelihood of a previous lower segment transverse uterine incision based on history and clinical circumstances of the previous surgery, a TOLAC may be offered

9. A maternal BMI >30 is associated with lower rates of VBAC, an increased risk of uterine rupture, increased maternal morbidity (compared to an ERCS), and possibly a longer decision-to delivery time. This should be addressed when considering TOLAC

10. There is a lack of data regarding previous uterine extensions, postpartum fever after prior cesarean section, Müllerian anomalies, and type of suture material used at surgery to make recommendations for risks/safety in TOLAC

11. The risk of placenta previa and placenta accreta, and their associated maternal morbidities, increases as the number of cesarean sections that a woman has had increases