TOLAC: trial of labor after cesarean
VBAC: vaginal birth after cesarean
1. What every clinician should know
TOLAC (trial of labor after cesarean) refers to the decision to attempt a vaginal delivery after a cesarean section. VBAC refers to a vaginal delivery that occurred after a prior cesarean. TOLAC rates reached 70% in the late 1990s, but have since declined to under 10% in 2006. This has contributed to the rising cesarean rates in the United States. The decision to undergo a TOLAC must incorporate both the chance of a successful VBAC, the risk of uterine rupture, and both maternal and perinatal morbidities.
2. Risks of TOLAC
Most of the increase in maternal morbidity results when a TOLAC fails and a woman requires a repeat cesarean in labor. Thus, the chance that a woman will achieve a vaginal delivery should be one component of counseling on route of delivery.
The morbidities to consider include hemorrhage, infection, operative injury, uterine rupture or dehiscence, hysterectomy, and maternal death. A meta-analysis of five studies assessing the risk of hemorrhage for women undergoing a repeat cesarean compared to a TOLAC demonstrated no significant difference between the two (1.7% vs. 1.2%, repectively). Women in the Maternal-Fetal Medicine Units (MFMU) Network Cesarean Registry who underwent TOLAC were more likely to have endometritis compared to those undergoing an elective repeat cesarean (2.9% vs. 1.8%, aOR 1.6, 95% CI: 1.4-1.9). Studies are inconclusive with respect to whether operative injury is more frequent among women undergoing TOLAC compared to a planned repeat cesarean.
Uterine rupture is the disruption of the myometrium as well as the overlying serosa. It is associated with maternal or neonatal morbidity. Uterine dehiscence is the separation of the myometrium without any adverse sequelae. While either uterine rupture or dehiscence can occur in women who plan for an elective cesarean, they are more frequent in women undergoing TOLAC.
While a TOLAC carries an increased risk of uterine rupture, a risk factor for hysterectomy, women undergoing an elective repeat cesarean have a higher risk of hysterectomy compared to those who successfully have a VBAC. Thus, overall, there is no difference in hysterectomy rates between women who choose a TOLAC compared to those choosing a repeat cesarean.
In a recent systematic review, maternal mortality rates were slightly lower in women undergoing a TOLAC compared to women undergoing repeat cesareans (0.013% vs. 0.004%).
It should be noted that the above comparisons are made at the population level. For an individual woman undergoing TOLAC, the probability of morbidity is related to the chance of VBAC, and thus the chance of morbidity may be higher or lower than the stated probabilities depending upon whether her chance of VBAC is substantively higher or lower than the population average.
As with maternal morbidity, neonatal morbidity is related to the chance that a woman who undergoes TOLAC achieves a VBAC. Uterine rupture places neonates at increased risk of multiple complications. Data about these specific risks are derived from observational trials comparing TOLAC to repeat cesarean. There is no difference in NICU admission rates after TOLAC compared to repeat cesarean.
Hypoxic ischemic encephalopathy (HIE) refers to a perinatal hypoxic event that leads to neurologic morbidity. The largest risk factor for HIE in women with a prior cesarean is uterine rupture; the risk of HIE after uterine rupture is approximately 5% to 10%. Landon et al demonstrated a small but significant increased chance of HIE in women undergoing TOLAC compared to repeat cesarean without labor (0.1% vs. 0.0%, P <.001).
The incidence of perinatal death after uterine rupture is 1.8%. The risks of perinatal death after an unlabored repeat cesarean is 0.13% and after a TOLAC is 0.29%. PMID: 15598960 However, if labor begins before the repeat cesarean, the perinatal death rate is 0.15%.
The risks above include only those ascribed to the index pregnancy. Multiple repeat cesarean sections increase the risk of subsequent abnormalities in placentation, which increase future maternal and neonatal morbidities. If uterine rupture occurs, the risk of recurrent rupture in a subsequent pregnancy is from 4% to 33%. If pregnancy occurs after rupture, delivery should occur at 37 to 39 weeks to reduce the risk of recurrent rupture.
Risks to the current and subsequent pregnancies, depending on the chosen route of delivery, should be discussed. As most of the risk of complications is related to repeat cesareans in labor, the chance of successful VBAC is a critical element in counseling. One model used to predict VBAC success using factors known during early prenatal care is available online at http://www.bsc.gwu.edu/mfmu/vagbirth.html.
Factors related to a successful VBAC include:
Demographics: white race, younger age, lower BMI.
Historical factors: prior vaginal delivery (especially if prior VBAC), nonrecurrent indication for prior cesarean (i.e., breech, non-reassuring fetal heart tones), absence of maternal comorbidities (e.g., hypertensive disease of pregnancy).
Number of prior cesareans: There is conflicting evidence on whether two prior cesarean deliveries decreases the chance of VBAC success.
Current pregnancy factors: spontaneous labor, delivery prior to 41 weeks gestational age.
Multiple gestation does not seem to be related to VBAC success.
Chance of uterine rupture
Many maternal characteristics are associated with an increased risk of uterine rupture during TOLAC. Unfortunately, no model has been shown to accurately predict this risk. Factors associated with an increased risk of uterine rupture include:
Demographics: older maternal age and white race
Historical factors: no prior vaginal delivery, chorioamnionitis after prior cesarean, classical uterine incision or T-uterine incision,
Multiple prior cesareans: Data are conflicting, but one observational study demonstrated an increased risk of uterine rupture in women who had two prior cesareans compared to one prior cesarean (1.8% vs. 0.9%, respectively.)
Current pregnancy factors: induced labor, higher doses of oxytocin.
A low transverse cesarean scar is a horizontal incision that exists only within the noncontractile lower aspect of the uterus. A low vertical cesarean scar is a vertical incision that exists only within the noncontractile lower aspect of the uterus. A classical cesarean is a vertical incision that extends beyond the limits of the lower segment. Because of the high risk of uterine rupture associated with TOLAC after a classical or T-uterine incision, these types are scars are considered a contraindication to a planned TOLAC. While data are limited, there is no good evidence to support a difference in the rate of uterine rupture when comparing low transverse to low vertical cesarean scars.
External cephalic version
Case series of ECV report success rates similar to women without a prior cesarean.
While induction is an option, there is a decreased chance of VBAC success and an increased risk of uterine rupture. This increased risk has been shown predominantly in women without a prior vaginal delivery.
There are conflicting data on the relationship between oxytocin use and the risk of uterine rupture. However, even if there is an association, the absolute risk increase is low (0.4% vs. 1.1%, respectively).There is an association between higher doses of oxytocin and uterine rupture. While a definitive specific threshold has not been identified, one group of authors caution against oxytocin rates above 20 mU/min as these rates are associated with a higher risk of uterine rupture (hazard ratio 3.92).
Early studies of prostaglandin E1 and E2 use demonstrated a 3- to 5-fold increased risk of uterine rupture compared to spontaneous labor. As such, ACOG recommends against the use of misoprostol in women with a prior cesarean. Instead, a transcervical Foley can be used for cervical ripening.
Augmentation of labor
Augmentation has been associated with an increased risk of uterine rupture compared to spontaneous labor without augmentation; however, the absolute risk is low (0.4% vs. 0.9%, respectively).
Continuous fetal monitoring should be done in labor. External monitoring is usually sufficient.
ACOG recommends maternal request as a sufficient indication for epidural use in labor, even in women undergoing TOLAC. Epidural has not been shown to delay the diagnosis of rupture or worsen outcomes.
There are no good data to support routine scar inspection as repair of an asymptomatic dehiscence has not been proven beneficial. However, if there are signs or symptoms of uterine rupture, exploration of the uterine scar is warranted.
Signs and symptoms
An abnormal fetal heart rate tracing is the most common sign of uterine rupture. Patterns associated with rupture include severe variable decelerations, recurrent late decelerations, or fetal bradycardia. Severe abdominal pain is another sign, and concerns that an epidural may mask this symptom have not been validated. Women with an epidural often feel increased pain or request additional epidural dosing proximate to uterine rupture. Other signs include vaginal bleeding and loss of fetal station.
When uterine rupture is suspected, fetal delivery should occur urgently. The timing of delivery needed to avoid neonatal injury is incompletely understood. In one small study of uterine rupture, no neonate delivered prior to 18 minutes experienced hypoxic injury. In many cases, uterine repair and preservation is possible, but approximately 10% to 20% of uterine ruptures will require a hysterectomy for hemostasis.
5. Second trimester delivery
There does not appear to be any difference in rates of failed second trimester induction or time to delivery intervals among women with and without a prior cesarean.
PGE1 is not associated with an increased risk of uterine rupture in the second trimester compared to spontaneous labor or compared to the use of other induction agents.
Mifepristone use prior to misoprostol induction improves vaginal delivery rates and shortens the duration of labor in the general population. Data on its use in women with a prior cesarean are limited.
6. Intrauterine fetal demise
Route of delivery
As vaginal delivery is associated with improved maternal outcomes, TOLAC should be encouraged in cases of intrauterine fetal demise (IUFD).
As misoprostol is associated with an increased risk of uterine rupture in the third trimester, induction with misoprostol should be avoided at this gestational age.
Rossi, AC, D’Addario, V. “Maternal morbidity following a trial of labor after cesarean section vs elective repeat cesarean delivery: a systematic review with metaanalysis”. Am J Obstet Gynecol. vol. 199. 2008. pp. 224-31. (A meta-analysis of maternal risks associated with TOLAC.)
Landon, MB, Hauth, JC, Leveno, KJ, Spong, CY, Leindecker, S, Varner, MW. “Maternal and perinatal outcomes associated with a trial of labor after prior cesarean delivery”. N Engl J Med. vol. 351. 2004. pp. 2581-9. (An MFMU prospective observational study of TOLAC)
Guise, JM, Eden, K, Emeis, C. “Vaginal birth after cesarean: new insights”. Evid Rep Technol Assess (Full Rep). vol. (191). 2010. pp. 1-397. (A recent systematic review of VBAC clinical data)
Spong, CY, Landon, MB, Gilbert, S, Rouse, DJ, Leveno, KJ, Varner, MW. “Risk of uterine rupture and adverse perinatal outcome at term after cesarean delivery”. Obstet Gynecol. vol. 110. 2007. pp. 801-7. (A secondary analysis of the MFMU trial on TOLAC examining the risks of uterine rupture.)
“American College of Obstetricians and Gynecologists. ACOG Practice bulletin no. 115: Vaginal birth after previous cesarean delivery”. Obstet Gynecol. vol. 116. 2010. pp. 450-63. (The ACOG practice bulletin on VBAC)
Grobman, WA, Lai, Y, Landon, MB, Spong, C, Leveno, KJ, Rouse, DJ. “Development of a nomogram for prediction of vaginal birth after cesarean delivery”. Obstet Gynecol. vol. 109. 2007. pp. 806-12. (A predictive model of VBAC based on information available at the first prenatal visit)
Macones, GA, Cahill, A, Pare, E, Stamilio, DM, Ratcliffe, S, Stevens, E. “Obstetric outcomes in women with two prior cesarean deliveries: is vaginal birth after cesarean delivery a viable option”. Am J Obstet Gynecol. vol. 192. 2005. pp. 1223-8. (A large prospective cohort of women with one and two prior cesareans)
Landon, MB, Spong, CY, Thom, E, Hauth, JC, Bloom, SL, Varner, MW. “Risk of uterine rupture with a trial of labor in women with multiple and single prior cesarean delivery”. Obstet Gynecol. vol. 108. 2006. pp. 12-20. (A large MFMU prospective cohort of women with one and two prior cesareans)
Landon, MB, Leindecker, S, Spong, CY, Hauth, JC, Bloom, S, Varner, MW. “The MFMU Cesarean Registry: factors affecting the success of trial of labor after previous cesarean delivery”. Am J Obstet Gynecol. vol. 193. 2005. pp. 1016-23. (Predictors of VBAC success)
Cahill, AG, Waterman, BM, Stamilio, DM, Odibo, AO, Allsworth, JE, Evanoff, B. “Higher maximum doses of oxytocin are associated with an unacceptably high risk for uterine rupture in patients attempting vaginal birth after cesarean delivery”. Am J Obstet Gynecol. vol. 199. 2008. pp. 32.e1-5. (A case-control study of oxytocin thresholds associated with uterine rupture.)
Holmgren, C, Scott, JR, Porter, TF, Esplin, MS, Bardsley, T. “Uterine rupture with attempted vaginal birth after cesarean delivery: decision-to-delivery time and neonatal outcome”. Obstet Gynecol. vol. 119. 2012. pp. 725-31. (A study measuring the time of the diagnosis of uterine rupture until delivery, and the association between latency and adverse neonatal outcomes).
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- TOLAC: trial of labor after cesarean
- VBAC: vaginal birth after cesarean
- 1. What every clinician should know
- 2. Risks of TOLAC
- 3. Management
- 4. Complications
- 6. Intrauterine fetal demise