Vaginal Birth After Cesarean Delivery

Etiology

As the cesarean delivery rate has increased, so has the number of patients becoming pregnant who have experienced cesarean section in a prior pregnancy. Patients may undergo vaginal birth after cesarean section either as a planned procedure or due to precipitant labor.

Epidemiology

Since 1970, the cesarean delivery rate has increased dramatically from 5% in 1970 to 32.1% in 2022.[1] In the early 1970s, when the cesarean delivery rate first began to rise, it was generally felt that if a patient had had a cesarean section, they should deliver all future babies by this route. Healthcare professionals began to question the dictum, "once a cesarean, always a cesarean," and subsequently, the number of patients undergoing VBAC delivery began to increase. From the mid-1980s to the mid-1990s, TOLAC was encouraged, and an increase in VBAC delivery was seen, along with a concomitant decrease in the cesarean delivery rate. Between 1985 and 1995, the VBAC rate increased by over 20%, which was associated with reduced cesarean section rates. As VBAC became more common over this time, so did the number of reported significant complications and related malpractice suits, leading to TOLAC again becoming less prevalent in the early 2000s, with a rate reported at 9.2% in 2006.[2] Since 2016, the VBAC rate seems to be increasing once again, with a rate reported at 14.2% in 2021.[3]

Complications in patients undergoing TOLAC can occur; however, appropriately selected patients can benefit from attempting a vaginal delivery in the appropriate setting. When successful, VBAC is associated with a decrease in maternal morbidity and a decreased risk of complications in future pregnancies. Patients who have undergone successful VBAC benefit from the avoidance of surgical recovery in the postpartum period. An increase in VBAC deliveries will also decrease the overall cesarean delivery rate. More recently, experts recognized that as the number of cesarean sections a patient undergoes increases, so does the risk of significant obstetrical complications, including massive postpartum hemorrhage, placenta previa, and complications related to placenta accreta spectrum disorders.[4] By avoiding multiple cesarean deliveries, patients planning large families may particularly stand to benefit from undergoing vaginal birth after cesarean section.

History and Physical

Clinical History

All pregnant patients should have a comprehensive history and physical exam at the initial prenatal visit and on admission to labor and delivery. History should include a detailed obstetric history consisting of the year of any prior pregnancies and pregnancy outcome (ie, abortion, ectopic, or delivery). The weight and gestational age of the infant at delivery should be recorded. Complications with prior pregnancies should be noted, and pertinent details should be described. In some cases, obtaining records from prior prenatal care clinicians or the hospital where the patient was previously delivered will be beneficial.

Concerning mode of delivery, noting if prior babies were delivered vaginally or by cesarean section is essential. For patients who have undergone previous operative delivery (either operative vaginal delivery or cesarean section), details about the indications for operative delivery should be obtained. Ideally, the operative notes of any prior delivery should be reviewed, and a copy should be available in the patient's chart.

Physical Examination

A general prenatal exam of a patient with a prior cesarean section should include a pelvic exam. This exam may also include clinical pelvimetry, which is a series of assessments designed to predict the likelihood of vaginal delivery. While clinical pelvimetry may be performed, this assessment is not highly predictive of successful VBAC or vaginal delivery. It should not be used as a sole predictor to determine if a patient can undergo a trial of labor.

For patients planning a trial of labor after cesarean section, a pelvic exam close to delivery may provide additional guidance regarding delivery planning. Ripening of the cervix (ie, softening and effacement) and low station of the fetal head give some encouragement that the patient may be more likely to enter labor spontaneously. A near-term attempt should be made to estimate the fetal weight by physical exam or ultrasonographic assessment. This information should be considered but should not be used singularly to determine if a trial of labor should be attempted, as no methods for the determination of fetal birth weight are highly accurate.

Evaluation

Candidates and Contraindications for Trial of Labor After Cesarean Delivery

Some patients will not be candidates for TOLAC. Patients having had prior classical cesarean section or prior incision into the contractile portion of the uterus have higher rates of uterine rupture, and thus, a planned repeat cesarean section (PRCD) is the recommended mode of delivery. Ideally, operative reports from prior surgeries should be obtained and reviewed to ascertain the type of previous uterine incision. When this is not possible, for example, when prior surgery was performed in another country, the patient is considered to have an "unknown scar." Because the vast majority of cesarean sections are performed with a low transverse uterine incision, it is reasonable to query the patient about the circumstances surrounding her delivery. If the history does not suggest a scenario in which a vertical incision would have been likely, allowing TOL is reasonable. The rate of uterine rupture in this situation is similar to the rate for patients with prior low transverse cesarean section.[5]

Patients with other conditions involving incision into the upper or contractile portion of the uterus are generally felt not to be candidates for TOLAC as the rate of uterine rupture is unacceptably high in these situations. In addition to prior classical uterine incision, such conditions would include prior "T" or "J" type incision at cesarean delivery or prior transmyometrial incisions to resect uterine fibroids or to facilitate open fetal surgery. Patients with a prior history of uterine rupture also have a high rate of uterine rupture, and planned repeat cesarean delivery is recommended before the onset of labor at an estimated gestational age of 36 to 37 0/7 weeks.[6]

Impact of Prior Cesarean Deliveries on Uterine Rupture Risk

Likewise, the rate of uterine rupture is felt to increase with increasing number of prior cesarean sections. With 1 prior low transverse cesarean section, the rate of uterine rupture is <1%, whereas the rate is slightly higher with 2 previous cesarean sections at 1% to 2%. Most practitioners, as well as ACOG, consider patients with up to 2 prior cesarean deliveries to be candidates for TOLAC.[5]

Facility Preparedness and Resource Availability

Facilities offering TOLAC should be able to perform emergency cesarean deliveries. While the availability of such resources seems prudent, concern has been raised that this requirement limits some patients, such as those living in rural areas, from having the option of vaginal delivery after cesarean section. In the most recent ACOG Practice Bulletin on this topic, consideration of referring such patients to sites that offer TOLAC when appropriate is recommended. Notably, with careful counseling, some patients might choose TOLAC despite limited resources.[5]

Likelihood of Successful Vaginal Birth After Cesarean Delivery

In considering TOLAC versus PRCD, patients may also benefit from counseling regarding the likelihood of vaginal delivery. The rate of successful vaginal delivery after a prior cesarean section is found to be 60% to 80%.[7] Many factors that may increase the likelihood of successful VBAC and decrease the risk of significant complications from attempted TOLAC have been studied. These factors include demographic characteristics, antenatal obstetric conditions, and intrapartum conditions. In general, patients with non-recurring indications for cesarean section, for example, breech presentation, are thought to have a higher likelihood of vaginal delivery. Patients with prior vaginal delivery also are found to have higher success rates of vaginal delivery. Patients entering labor spontaneously have higher success rates as well when compared to patients undergoing induction of labor. Some factors associated with a lower likelihood of success include maternal hypertension, gestational age greater than 40 weeks, maternal obesity, and maternal age older than 35.[8]

Vaginal Birth After Cesarean Delivery Calculators

VBAC calculators, eg, the one developed by the Maternal-Fetal Medicine Units Network, are also available to estimate success.[9] This calculator is widely used and asks for information including age, current and prepregnancy weight, birth history, and chronic conditions (eg, high blood pressure). The updated version of the calculator published by the Society for Maternal-Fetal Medicine (SMFM) does not consider race or ethnicity, as these factors do not contribute to the riskiness of a VBAC. Notably, the results provided by VBAC calculators should be used as guidelines but not definitive predictors of possible successful VBAC. A retrospective study by Wycoff et al found that calculators "consistently underestimated successful VBAC at their institutions."[10] Another pitfall of VBAC calculators is that they are not able to incorporate an individual patient's values and preferences, and the use of such calculators has not been shown to result in improved patient outcomes.[5]

Treatment / Management

Prenatal Care for Trial of Labor After Cesarean Delivery

Patients planning a trial of labor after cesarean section require typical prenatal care with additional counseling regarding the option of TOLAC versus PRCD. Additionally, an early ultrasound to confirm gestational age can be helpful if a cesarean section is scheduled.

Labor Management for Vaginal Birth After Cesarean Delivery

With regards to labor management, spontaneous entry into labor is preferred as spontaneous labor carries a higher risk of successful vaginal delivery and a lower risk of uterine rupture.[11] Induction of labor remains an option when indicated. If labor induction is undertaken, the use of prostaglandins for cervical ripening is contraindicated as several studies have demonstrated increased risks of uterine rupture when prostaglandins (eg, misoprostol or dinoprostone) are used for cervical ripening. Use of low-dose oxytocin or mechanical dilation with intracervical balloons may be used to facilitate induction in patients undergoing TOLAC with an unripe cervix. Studies of the use of mechanical dilators in VBAC settings are limited and show mixed results.[5]

While not required, epidural analgesia may be useful in improving patient comfort with the benefit of providing a rapid option for anesthesia if cesarean delivery is required.

Intrapartum Monitoring

Patients should have fetal heart tones monitored closely during labor, and attention should be paid to appropriate labor progress. Continuous fetal heart rate monitoring is strongly recommended. If concerns arise about possible uterine dehiscence or rupture, cesarean delivery should be performed promptly. 

The most common sign of uterine rupture is an abnormality of fetal heart rate tracing, which is seen in approximately 70% of cases of uterine rupture.[5] Other findings that may be seen if uterine rupture occurs include an increase or decrease in uterine contractions, severe abdominal pain/pain out of proportion for labor, sudden loss of fetal station, or finding of blood in the urine or urine collection bag. Even with close and meticulous monitoring, uterine rupture can occur suddenly and without warning, resulting in fetal compromise, fetal damage, or death.

Postpartum Management

Vaginal delivery, delivery of the placenta, and postpartum support are typical for patients undergoing VBAC delivery. Rarely, manual exploration of the uterus following placental delivery may lead to suspicion or discovery of previously undetected dehiscence of the uterine scar. Repair of such a defect is not required unless there is ongoing bleeding. Likewise, patients may experience occult uterine rupture, which can lead to bleeding following delivery. VBAC patients experiencing post-delivery hypotension or other signs of hypovolemia should be evaluated promptly with consideration given to the possible diagnosis of uterine rupture.

Differential Diagnosis

Patient history should be highly accurate in determining which patients may be counseled about TOLAC. However, in some cases, historical information may not be fully available. In these situations, an attempt should be made to obtain prior records. If complete information is not available, the clinician may need to rely on clinical judgment to determine whether TOLAC may be attempted. Generally, if the clinician cannot verify the relative safety of TOLAC, a repeat cesarean section should be offered. Differential diagnoses for uterine rupture may include the following:

• Variable decelerations related to low fluid or cord compression
• Placental abruption
• Placental insufficiency

Complications

Uterine Rupture

The most significant complication which can occur in patients undergoing TOLAC is uterine rupture. Uterine rupture occurs when the weakened, prior uterine scar begins to tear. Uterine rupture is a medical emergency, and patients must be taken immediately for laparotomy for delivery of the fetus and to address additional complications. When uterine rupture occurs, the transfer of blood and oxygen to the baby is interrupted, and this can result in fetal complications, including fetal acidosis, a need for neonatal intensive care unit (NICU) admission, fetal asphyxia, and even death.

While the absolute risk of perinatal mortality is low with TOLAC, the risk is slightly higher when compared to babies born to mothers undergoing planned repeat cesarean delivery (0.13% versus 0.05%).[12] In cases of uterine rupture, the risk to the mother is also significant. Patients may experience significant hemorrhage. When hemorrhage occurs in this setting, transfusion, and sometimes hysterectomy, is necessary to control bleeding and can be life-saving.

Uterine Dehiscence

Uterine dehiscence is also described. Dehiscence differs from a uterine rupture in that the outer serosal layer of the uterus may remain intact while the underlying muscular layers have opened, allowing for visualization of the amniotic sac and fetus. Such a finding is often referred to as a "uterine window." Patients with uterine dehiscence are frequently asymptomatic, and the more serious sequela that can occur with uterine rupture are less likely to be encountered. When reviewing scholarly articles about uterine scar rupture and dehiscence, the distinction between these entities is not always clear, sometimes making study conclusions difficult to interpret.

Emergent Cesarean Delivery Associated Complications

Some patients attempting TOLAC may require a cesarean delivery. When this occurs after labor, the risks of postpartum infection, uterine atony, and wound separation are higher in comparison to patients who have planned repeat cesarean section.