Mark B. Landon, MD

The relative safety of vaginal birth after cesarean (VBAC) has been documented in several large-scale studies in the past 15 years, and was affirmed in 2010 through a National Institutes of Health consensus development conference and a practice bulletin from the American College of Obstetricians and Gynecologists. Yet, despite all this research and review, rates of a trial of labor after cesarean (TOLAC) have increased only modestly in the last several years.

Approximately 20% of all births in 2013 in women with a history of one cesarean section involved a trial of labor, according to a recent report from the Centers for Disease Control and Prevention. This represents only a small increase from 2006, when the TOLAC rate had plummeted to approximately 15%.

The limited change is concerning because up to two-thirds of women with a prior cesarean delivery are candidates for a trial of labor, and many of them are excellent candidates. In total, 70% of the women who attempted labor in 2013 after a previous cesarean had successful VBACs, the CDC data shows.

Several European countries have TOLAC rates between 50% and 70%, but in the United States, as evidenced by the recent CDC data, there continues to be an underutilization of attempted VBAC. We must ask ourselves, are women truly able to choose TOLAC, or are they being dissuaded by the health care system?

I believe that the barriers are still pervasive. Too often, women who are TOLAC candidates are not receiving appropriate counseling – and too often, women are not even being presented the option of a trial of labor, even when staff are immediately available to provide emergency care if needed.

Rupture concerns in perspective

When the NIH consensus development panel reviewed VBAC in 2010, it concluded that TOLAC is a reasonable option for many women with a prior cesarean. The panel found that restricted access to VBAC/TOLAC stemmed from existing practice guidelines and the medical liability climate, and it called upon providers and others to “mitigate or even eliminate” the barriers that women face in finding clinicians and facilities able and willing to offer TOLAC.

ACOG’s 2010 practice bulletin also acknowledged the problem of limited access. ACOG recommended, as it had in an earlier bulletin, that TOLAC-VBAC be undertaken in facilities where staff are immediately available for emergency care. It added, however, that when such resources are not available, the best alternative may be to refer patients to a facility with available resources. Health care providers and insurance carriers “should do all they can to facilitate transfer of care or comanagement in support of a desired TOLAC,” ACOG’s document states.

Why, given such recommendations, are we still falling so short of where we should be?

A number of nonclinical factors are involved, but clearly, as both the NIH and ACOG have stated, the fear of litigation in cases of uterine rupture is a contributing factor. A ruptured uterus is indeed the principal risk associated with TOLAC, and it can have serious sequelae including perinatal death, hypoxic ischemic encephalopathy (HIE), and hysterectomy.

We must appreciate, however, that the absolute rates of uterine rupture and of serious adverse outcomes are quite low. The rupture rate in 2013 among women who underwent TOLAC but ultimately had a repeat cesarean section – the highest-risk group – was 495 per 100,000 live births, according to the CDC. This rate of approximately 0.5% is consistent with the level of risk reported in the literature for several decades.

In one of the two large observational studies done in the United States that have shed light on TOLAC outcomes, the rate of uterine rupture among women who underwent TOLAC was 0.7% for women with a prior low transverse incision, 2.0% for those with a prior low vertical incision, and 0.5% for those with an unknown type of prior incision. Overall, the rate of uterine rupture in this study’s cohort of 17,898 women who underwent TOLAC was 0.7% (N Engl J Med. 2004 Dec 16;351[25]:2581-9). The study was conducted at 19 medical centers belonging to the Eunice Kennedy Shriver National Institute of Child Health and Human Development’s Maternal-Fetal Medical Units (MFMU) Network.

The second large study conducted in the United States – a multicenter observational study in which records of approximately 25,000 women with a prior low-transverse cesarean section were reviewed – also showed rates of uterine rupture less than 1% (Am J Obstet Gynecol. 2005 Nov;193[5]:1656-62).

The attributable risk for perinatal death or HIE at term appears to be 1 per 2,000 TOLAC, according to the MFMU Network study.

Failed trials of labor resulting in repeat cesarean deliveries have consistently been associated with higher morbidity than scheduled repeat cesarean deliveries, with the greatest difference in rates for ruptured uterus. In the first MFMU Network study, there were no cases of uterine rupture among a cohort of 15,801 women who underwent elective repeat cesarean delivery, and in the second multicenter study of 25,000 women, this patient group had a rupture rate of 0.004%.

Yet, as ACOG points out, neither elective repeat cesarean deliveries nor TOLAC are without maternal or neonatal risk. Women who have successful VBAC delivery, on the other hand, have significantly lower morbidity and better outcomes than women who do not attempt labor. Women who undergo VBAC also avoid exposure to the significant risks of repeat cesarean deliveries in the long term.

Research unequivocally shows that the risk of placenta accreta, hysterectomy, hemorrhage, and other serious maternal morbidity increases progressively with each repeat cesarean delivery. Rates of placenta accreta have, in fact, been rising in the United States – a trend that should prompt us to think more about TOLAC.

Moreover, TOLAC is being shown to be a cost-effective strategy. In one analysis, TOLAC in a second pregnancy was cost-effective as long as the chance of VBAC exceeded approximately 74% (Obstet Gynecol. 2001 Jun;97[6]:932-41). More recently, TOLAC was found to be cost-effective across a wide variety of circumstances, including when a woman had a probability of VBAC as low as 43%. The model in this analysis, which used probability estimates from the MFMU Cesarean Registry, took a longer-term view by including probabilities of outcomes throughout a woman’s reproductive life that were contingent upon her initial choice regarding TOLAC (Am J Perinatol. 2013 Jan;30[1]:11-20).

Likelihood of success

Evaluating and discussing the likelihood of success with TOLAC is therefore key to the counseling process. The higher the likelihood of achieving VBAC, the more favorable the risk-benefit ratio will be and the more appealing it will be to consider.

According to one analysis, if a woman undergoing a TOLAC has at least a 60%-70% chance of VBAC, her chance of having major or minor morbidity is no greater than a woman undergoing a planned repeat cesarean delivery (Am J Obstet Gynecol 2009;200:56.e1-e6).

There are several prediction tools available that can be used at the first prenatal visit and in early labor to give a reasonably good estimate of success. One of these tools is available at the MFMU Network website (http://mfmu.bsc.gwu.edu). The tools take into account factors such as prior indication for cesarean delivery; history of vaginal delivery; demographic characteristics such as maternal age and body mass index; the occurrence of spontaneous labor; and cervical status at admission.

Prior vaginal delivery is one of the strongest predictors of a successful TOLAC. Research has consistently shown that women with a prior vaginal delivery – including a vaginal delivery predating an unsuccessful TOLAC – have significantly higher TOLAC success rates than women who did not have any prior vaginal delivery.

The indication for a prior cesarean delivery also clearly affects the likelihood of a successful TOLAC. Women whose first cesarean delivery was performed for a nonrecurring indication, such as breech presentation or low intolerance of labor, have TOLAC success rates that are similar to vaginal delivery rates for nulliparous women. Success rates for these women may exceed 85%. On the other hand, women who had a prior cesarean delivery for cephalopelvic disproportion or failure to progress have been shown to have lower TOLAC success rates ranging from 50%-67%.

Labor induction should be approached cautiously, as women who undergo induction of labor in TOLAC have an increased risk of repeat cesarean delivery. Still, success rates with induction are high. Data from the MFMU Cesarean Registry showed that about 66% of women undergoing induction after one prior cesarean delivery achieved VBAC versus 76% of women entering TOLAC spontaneously (Obstet Gynecol. 2007 Feb;109[2 Pt 1]:262-9). Another study of women undergoing induction after one prior cesarean reported an overall success rate of 78% (Obstet Gynecol. 2004 Mar;103[3]:534-8).

Whether induction specifically increases the risk for uterine rupture in TOLAC, compared with expectant management, is unclear. There also are conflicting data as to whether particular induction methods increase this risk.

Based on available data, ACOG considers induction of labor for either maternal or fetal indications to be an option for women undergoing TOLAC. Oxytocin may be used for induction as well as augmentation, but caution should be exercised at higher doses. While there is no clear dosing threshold for increased risk of rupture, research has suggested that higher doses of oxytocin are best avoided.

The use of prostaglandins is more controversial: Based on evidence from several small studies, ACOG concluded in its 2010 bulletin that misoprostol (prostaglandin E₁) for cervical ripening is contraindicated in women undergoing TOLAC. It appears likely that rupture risk increases in patients who received both prostaglandins and oxytocin, so ACOG has advised avoiding their sequential use when prostaglandin E₂ is used. This of course limits the options for the practitioner. Therefore, utilizing a Foley catheter followed by pitocin has been an approach advocated in some cases.

Uterine rupture is not predictable, and it is far more difficult to assess an individual’s risk of this complication than it is to assess the likelihood of VBAC. Still, there is value to discussing with the patient whether there are any other modifiers that could potentially influence the risk of rupture.

Since rates of uterine rupture are highest in women with previous classical or T-shaped incision, for example, it is important to try to ascertain what type of incision was previously used. It is widely appreciated that low-transverse uterine incisions are most favorable, but findings are mixed in regard to low-vertical incisions. Some research shows that women with a previous low-vertical incision do not have significantly lower VBAC success rates or higher risks of uterine rupture. TOLAC should therefore not be ruled out in these cases.

Additionally, TOLAC should not be ruled out for women who have had more than one cesarean delivery. Several studies have shown an increased risk of uterine rupture after two prior cesarean deliveries, compared with one, and one meta-analysis suggested a more than twofold increased risk (BJOG. 2010 Jan;117(1):5-19.).

In contrast, an analysis of the MFMU Cesarean Registry found no significant difference in rupture rates in women with one prior cesarean versus multiple prior cesareans (Obstet Gynecol. 2006 Jul;108[1]:12-20.).

It appears, therefore, that even if having more than one prior cesarean section is associated with an increased risk of rupture, the magnitude of this increase is small.

Just as women with a prior vaginal delivery have the highest chance of VBAC success, they also have the lowest rates of rupture among all women undergoing TOLAC.

Patient counseling

We must inform our patients who have had a cesarean section in the past of their options for childbirth in an unbiased manner.

The complications of both TOLAC and elective repeat cesarean section should be discussed, and every attempt should be made to individually assess both the likelihood of a successful VBAC and the comparative risk of maternal and perinatal morbidity. A shared decision-making process should be adopted, and whenever possible, the patient’s preference should be respected. In the end, a woman undergoing TOLAC should be truly motivated to pursue a trial of labor, because there are inherent risks.

One thing I’ve learned from my clinical practice and research on this issue is that the desire to undergo a vaginal delivery is powerful for some women. Many of my patients have self-referred for consultation about TOLAC after their ob.gyn. informed them that their hospital is not equipped, and they should therefore have a scheduled repeat operation. In many cases they discover that TOLAC is an option if they are willing to travel a half-hour or so.

We need to honor this desire and inform our patients of the option, and help facilitate delivery at another nearby hospital when our own facility is not equipped for TOLAC.

Dr. Landon is the Richard L. Meiling Professor and chairman of the department of obstetrics and gynecology at the Ohio State University, Columbus. He served for more than 25 years as Ohio State’s coinvestigator for the National Institutes of Child Health and Human Development Maternal Fetal Medicine Units Network. He reported having no relevant financial disclosures.

The relative safety of vaginal birth after cesarean (VBAC) has been documented in several large-scale studies in the past 15 years, and was affirmed in 2010 through a National Institutes of Health consensus development conference and a practice bulletin from the American College of Obstetricians and Gynecologists. Yet, despite all this research and review, rates of a trial of labor after cesarean (TOLAC) have increased only modestly in the last several years.

Approximately 20% of all births in 2013 in women with a history of one cesarean section involved a trial of labor, according to a recent report from the Centers for Disease Control and Prevention. This represents only a small increase from 2006, when the TOLAC rate had plummeted to approximately 15%.

The limited change is concerning because up to two-thirds of women with a prior cesarean delivery are candidates for a trial of labor, and many of them are excellent candidates. In total, 70% of the women who attempted labor in 2013 after a previous cesarean had successful VBACs, the CDC data shows.

Several European countries have TOLAC rates between 50% and 70%, but in the United States, as evidenced by the recent CDC data, there continues to be an underutilization of attempted VBAC. We must ask ourselves, are women truly able to choose TOLAC, or are they being dissuaded by the health care system?

I believe that the barriers are still pervasive. Too often, women who are TOLAC candidates are not receiving appropriate counseling – and too often, women are not even being presented the option of a trial of labor, even when staff are immediately available to provide emergency care if needed.

Rupture concerns in perspective

When the NIH consensus development panel reviewed VBAC in 2010, it concluded that TOLAC is a reasonable option for many women with a prior cesarean. The panel found that restricted access to VBAC/TOLAC stemmed from existing practice guidelines and the medical liability climate, and it called upon providers and others to “mitigate or even eliminate” the barriers that women face in finding clinicians and facilities able and willing to offer TOLAC.

ACOG’s 2010 practice bulletin also acknowledged the problem of limited access. ACOG recommended, as it had in an earlier bulletin, that TOLAC-VBAC be undertaken in facilities where staff are immediately available for emergency care. It added, however, that when such resources are not available, the best alternative may be to refer patients to a facility with available resources. Health care providers and insurance carriers “should do all they can to facilitate transfer of care or comanagement in support of a desired TOLAC,” ACOG’s document states.

Why, given such recommendations, are we still falling so short of where we should be?

A number of nonclinical factors are involved, but clearly, as both the NIH and ACOG have stated, the fear of litigation in cases of uterine rupture is a contributing factor. A ruptured uterus is indeed the principal risk associated with TOLAC, and it can have serious sequelae including perinatal death, hypoxic ischemic encephalopathy (HIE), and hysterectomy.

We must appreciate, however, that the absolute rates of uterine rupture and of serious adverse outcomes are quite low. The rupture rate in 2013 among women who underwent TOLAC but ultimately had a repeat cesarean section – the highest-risk group – was 495 per 100,000 live births, according to the CDC. This rate of approximately 0.5% is consistent with the level of risk reported in the literature for several decades.

In one of the two large observational studies done in the United States that have shed light on TOLAC outcomes, the rate of uterine rupture among women who underwent TOLAC was 0.7% for women with a prior low transverse incision, 2.0% for those with a prior low vertical incision, and 0.5% for those with an unknown type of prior incision. Overall, the rate of uterine rupture in this study’s cohort of 17,898 women who underwent TOLAC was 0.7% (N Engl J Med. 2004 Dec 16;351[25]:2581-9). The study was conducted at 19 medical centers belonging to the Eunice Kennedy Shriver National Institute of Child Health and Human Development’s Maternal-Fetal Medical Units (MFMU) Network.

The second large study conducted in the United States – a multicenter observational study in which records of approximately 25,000 women with a prior low-transverse cesarean section were reviewed – also showed rates of uterine rupture less than 1% (Am J Obstet Gynecol. 2005 Nov;193[5]:1656-62).

The attributable risk for perinatal death or HIE at term appears to be 1 per 2,000 TOLAC, according to the MFMU Network study.

Failed trials of labor resulting in repeat cesarean deliveries have consistently been associated with higher morbidity than scheduled repeat cesarean deliveries, with the greatest difference in rates for ruptured uterus. In the first MFMU Network study, there were no cases of uterine rupture among a cohort of 15,801 women who underwent elective repeat cesarean delivery, and in the second multicenter study of 25,000 women, this patient group had a rupture rate of 0.004%.

Yet, as ACOG points out, neither elective repeat cesarean deliveries nor TOLAC are without maternal or neonatal risk. Women who have successful VBAC delivery, on the other hand, have significantly lower morbidity and better outcomes than women who do not attempt labor. Women who undergo VBAC also avoid exposure to the significant risks of repeat cesarean deliveries in the long term.

Research unequivocally shows that the risk of placenta accreta, hysterectomy, hemorrhage, and other serious maternal morbidity increases progressively with each repeat cesarean delivery. Rates of placenta accreta have, in fact, been rising in the United States – a trend that should prompt us to think more about TOLAC.

Moreover, TOLAC is being shown to be a cost-effective strategy. In one analysis, TOLAC in a second pregnancy was cost-effective as long as the chance of VBAC exceeded approximately 74% (Obstet Gynecol. 2001 Jun;97[6]:932-41). More recently, TOLAC was found to be cost-effective across a wide variety of circumstances, including when a woman had a probability of VBAC as low as 43%. The model in this analysis, which used probability estimates from the MFMU Cesarean Registry, took a longer-term view by including probabilities of outcomes throughout a woman’s reproductive life that were contingent upon her initial choice regarding TOLAC (Am J Perinatol. 2013 Jan;30[1]:11-20).

Likelihood of success

Evaluating and discussing the likelihood of success with TOLAC is therefore key to the counseling process. The higher the likelihood of achieving VBAC, the more favorable the risk-benefit ratio will be and the more appealing it will be to consider.

According to one analysis, if a woman undergoing a TOLAC has at least a 60%-70% chance of VBAC, her chance of having major or minor morbidity is no greater than a woman undergoing a planned repeat cesarean delivery (Am J Obstet Gynecol 2009;200:56.e1-e6).

There are several prediction tools available that can be used at the first prenatal visit and in early labor to give a reasonably good estimate of success. One of these tools is available at the MFMU Network website (http://mfmu.bsc.gwu.edu). The tools take into account factors such as prior indication for cesarean delivery; history of vaginal delivery; demographic characteristics such as maternal age and body mass index; the occurrence of spontaneous labor; and cervical status at admission.

Prior vaginal delivery is one of the strongest predictors of a successful TOLAC. Research has consistently shown that women with a prior vaginal delivery – including a vaginal delivery predating an unsuccessful TOLAC – have significantly higher TOLAC success rates than women who did not have any prior vaginal delivery.

The indication for a prior cesarean delivery also clearly affects the likelihood of a successful TOLAC. Women whose first cesarean delivery was performed for a nonrecurring indication, such as breech presentation or low intolerance of labor, have TOLAC success rates that are similar to vaginal delivery rates for nulliparous women. Success rates for these women may exceed 85%. On the other hand, women who had a prior cesarean delivery for cephalopelvic disproportion or failure to progress have been shown to have lower TOLAC success rates ranging from 50%-67%.

Labor induction should be approached cautiously, as women who undergo induction of labor in TOLAC have an increased risk of repeat cesarean delivery. Still, success rates with induction are high. Data from the MFMU Cesarean Registry showed that about 66% of women undergoing induction after one prior cesarean delivery achieved VBAC versus 76% of women entering TOLAC spontaneously (Obstet Gynecol. 2007 Feb;109[2 Pt 1]:262-9). Another study of women undergoing induction after one prior cesarean reported an overall success rate of 78% (Obstet Gynecol. 2004 Mar;103[3]:534-8).

Whether induction specifically increases the risk for uterine rupture in TOLAC, compared with expectant management, is unclear. There also are conflicting data as to whether particular induction methods increase this risk.

Based on available data, ACOG considers induction of labor for either maternal or fetal indications to be an option for women undergoing TOLAC. Oxytocin may be used for induction as well as augmentation, but caution should be exercised at higher doses. While there is no clear dosing threshold for increased risk of rupture, research has suggested that higher doses of oxytocin are best avoided.

The use of prostaglandins is more controversial: Based on evidence from several small studies, ACOG concluded in its 2010 bulletin that misoprostol (prostaglandin E₁) for cervical ripening is contraindicated in women undergoing TOLAC. It appears likely that rupture risk increases in patients who received both prostaglandins and oxytocin, so ACOG has advised avoiding their sequential use when prostaglandin E₂ is used. This of course limits the options for the practitioner. Therefore, utilizing a Foley catheter followed by pitocin has been an approach advocated in some cases.

Uterine rupture is not predictable, and it is far more difficult to assess an individual’s risk of this complication than it is to assess the likelihood of VBAC. Still, there is value to discussing with the patient whether there are any other modifiers that could potentially influence the risk of rupture.

Since rates of uterine rupture are highest in women with previous classical or T-shaped incision, for example, it is important to try to ascertain what type of incision was previously used. It is widely appreciated that low-transverse uterine incisions are most favorable, but findings are mixed in regard to low-vertical incisions. Some research shows that women with a previous low-vertical incision do not have significantly lower VBAC success rates or higher risks of uterine rupture. TOLAC should therefore not be ruled out in these cases.

Additionally, TOLAC should not be ruled out for women who have had more than one cesarean delivery. Several studies have shown an increased risk of uterine rupture after two prior cesarean deliveries, compared with one, and one meta-analysis suggested a more than twofold increased risk (BJOG. 2010 Jan;117(1):5-19.).

In contrast, an analysis of the MFMU Cesarean Registry found no significant difference in rupture rates in women with one prior cesarean versus multiple prior cesareans (Obstet Gynecol. 2006 Jul;108[1]:12-20.).

It appears, therefore, that even if having more than one prior cesarean section is associated with an increased risk of rupture, the magnitude of this increase is small.

Just as women with a prior vaginal delivery have the highest chance of VBAC success, they also have the lowest rates of rupture among all women undergoing TOLAC.

Patient counseling

We must inform our patients who have had a cesarean section in the past of their options for childbirth in an unbiased manner.

The complications of both TOLAC and elective repeat cesarean section should be discussed, and every attempt should be made to individually assess both the likelihood of a successful VBAC and the comparative risk of maternal and perinatal morbidity. A shared decision-making process should be adopted, and whenever possible, the patient’s preference should be respected. In the end, a woman undergoing TOLAC should be truly motivated to pursue a trial of labor, because there are inherent risks.

One thing I’ve learned from my clinical practice and research on this issue is that the desire to undergo a vaginal delivery is powerful for some women. Many of my patients have self-referred for consultation about TOLAC after their ob.gyn. informed them that their hospital is not equipped, and they should therefore have a scheduled repeat operation. In many cases they discover that TOLAC is an option if they are willing to travel a half-hour or so.

We need to honor this desire and inform our patients of the option, and help facilitate delivery at another nearby hospital when our own facility is not equipped for TOLAC.

Dr. Landon is the Richard L. Meiling Professor and chairman of the department of obstetrics and gynecology at the Ohio State University, Columbus. He served for more than 25 years as Ohio State’s coinvestigator for the National Institutes of Child Health and Human Development Maternal Fetal Medicine Units Network. He reported having no relevant financial disclosures.

The relative safety of vaginal birth after cesarean (VBAC) has been documented in several large-scale studies in the past 15 years, and was affirmed in 2010 through a National Institutes of Health consensus development conference and a practice bulletin from the American College of Obstetricians and Gynecologists. Yet, despite all this research and review, rates of a trial of labor after cesarean (TOLAC) have increased only modestly in the last several years.

Approximately 20% of all births in 2013 in women with a history of one cesarean section involved a trial of labor, according to a recent report from the Centers for Disease Control and Prevention. This represents only a small increase from 2006, when the TOLAC rate had plummeted to approximately 15%.

The limited change is concerning because up to two-thirds of women with a prior cesarean delivery are candidates for a trial of labor, and many of them are excellent candidates. In total, 70% of the women who attempted labor in 2013 after a previous cesarean had successful VBACs, the CDC data shows.

Several European countries have TOLAC rates between 50% and 70%, but in the United States, as evidenced by the recent CDC data, there continues to be an underutilization of attempted VBAC. We must ask ourselves, are women truly able to choose TOLAC, or are they being dissuaded by the health care system?

I believe that the barriers are still pervasive. Too often, women who are TOLAC candidates are not receiving appropriate counseling – and too often, women are not even being presented the option of a trial of labor, even when staff are immediately available to provide emergency care if needed.

Rupture concerns in perspective

When the NIH consensus development panel reviewed VBAC in 2010, it concluded that TOLAC is a reasonable option for many women with a prior cesarean. The panel found that restricted access to VBAC/TOLAC stemmed from existing practice guidelines and the medical liability climate, and it called upon providers and others to “mitigate or even eliminate” the barriers that women face in finding clinicians and facilities able and willing to offer TOLAC.

ACOG’s 2010 practice bulletin also acknowledged the problem of limited access. ACOG recommended, as it had in an earlier bulletin, that TOLAC-VBAC be undertaken in facilities where staff are immediately available for emergency care. It added, however, that when such resources are not available, the best alternative may be to refer patients to a facility with available resources. Health care providers and insurance carriers “should do all they can to facilitate transfer of care or comanagement in support of a desired TOLAC,” ACOG’s document states.

Why, given such recommendations, are we still falling so short of where we should be?

A number of nonclinical factors are involved, but clearly, as both the NIH and ACOG have stated, the fear of litigation in cases of uterine rupture is a contributing factor. A ruptured uterus is indeed the principal risk associated with TOLAC, and it can have serious sequelae including perinatal death, hypoxic ischemic encephalopathy (HIE), and hysterectomy.

We must appreciate, however, that the absolute rates of uterine rupture and of serious adverse outcomes are quite low. The rupture rate in 2013 among women who underwent TOLAC but ultimately had a repeat cesarean section – the highest-risk group – was 495 per 100,000 live births, according to the CDC. This rate of approximately 0.5% is consistent with the level of risk reported in the literature for several decades.

In one of the two large observational studies done in the United States that have shed light on TOLAC outcomes, the rate of uterine rupture among women who underwent TOLAC was 0.7% for women with a prior low transverse incision, 2.0% for those with a prior low vertical incision, and 0.5% for those with an unknown type of prior incision. Overall, the rate of uterine rupture in this study’s cohort of 17,898 women who underwent TOLAC was 0.7% (N Engl J Med. 2004 Dec 16;351[25]:2581-9). The study was conducted at 19 medical centers belonging to the Eunice Kennedy Shriver National Institute of Child Health and Human Development’s Maternal-Fetal Medical Units (MFMU) Network.

The second large study conducted in the United States – a multicenter observational study in which records of approximately 25,000 women with a prior low-transverse cesarean section were reviewed – also showed rates of uterine rupture less than 1% (Am J Obstet Gynecol. 2005 Nov;193[5]:1656-62).

The attributable risk for perinatal death or HIE at term appears to be 1 per 2,000 TOLAC, according to the MFMU Network study.

Failed trials of labor resulting in repeat cesarean deliveries have consistently been associated with higher morbidity than scheduled repeat cesarean deliveries, with the greatest difference in rates for ruptured uterus. In the first MFMU Network study, there were no cases of uterine rupture among a cohort of 15,801 women who underwent elective repeat cesarean delivery, and in the second multicenter study of 25,000 women, this patient group had a rupture rate of 0.004%.

Yet, as ACOG points out, neither elective repeat cesarean deliveries nor TOLAC are without maternal or neonatal risk. Women who have successful VBAC delivery, on the other hand, have significantly lower morbidity and better outcomes than women who do not attempt labor. Women who undergo VBAC also avoid exposure to the significant risks of repeat cesarean deliveries in the long term.

Research unequivocally shows that the risk of placenta accreta, hysterectomy, hemorrhage, and other serious maternal morbidity increases progressively with each repeat cesarean delivery. Rates of placenta accreta have, in fact, been rising in the United States – a trend that should prompt us to think more about TOLAC.

Moreover, TOLAC is being shown to be a cost-effective strategy. In one analysis, TOLAC in a second pregnancy was cost-effective as long as the chance of VBAC exceeded approximately 74% (Obstet Gynecol. 2001 Jun;97[6]:932-41). More recently, TOLAC was found to be cost-effective across a wide variety of circumstances, including when a woman had a probability of VBAC as low as 43%. The model in this analysis, which used probability estimates from the MFMU Cesarean Registry, took a longer-term view by including probabilities of outcomes throughout a woman’s reproductive life that were contingent upon her initial choice regarding TOLAC (Am J Perinatol. 2013 Jan;30[1]:11-20).

Likelihood of success

Evaluating and discussing the likelihood of success with TOLAC is therefore key to the counseling process. The higher the likelihood of achieving VBAC, the more favorable the risk-benefit ratio will be and the more appealing it will be to consider.

According to one analysis, if a woman undergoing a TOLAC has at least a 60%-70% chance of VBAC, her chance of having major or minor morbidity is no greater than a woman undergoing a planned repeat cesarean delivery (Am J Obstet Gynecol 2009;200:56.e1-e6).

There are several prediction tools available that can be used at the first prenatal visit and in early labor to give a reasonably good estimate of success. One of these tools is available at the MFMU Network website (http://mfmu.bsc.gwu.edu). The tools take into account factors such as prior indication for cesarean delivery; history of vaginal delivery; demographic characteristics such as maternal age and body mass index; the occurrence of spontaneous labor; and cervical status at admission.

Prior vaginal delivery is one of the strongest predictors of a successful TOLAC. Research has consistently shown that women with a prior vaginal delivery – including a vaginal delivery predating an unsuccessful TOLAC – have significantly higher TOLAC success rates than women who did not have any prior vaginal delivery.

The indication for a prior cesarean delivery also clearly affects the likelihood of a successful TOLAC. Women whose first cesarean delivery was performed for a nonrecurring indication, such as breech presentation or low intolerance of labor, have TOLAC success rates that are similar to vaginal delivery rates for nulliparous women. Success rates for these women may exceed 85%. On the other hand, women who had a prior cesarean delivery for cephalopelvic disproportion or failure to progress have been shown to have lower TOLAC success rates ranging from 50%-67%.

Labor induction should be approached cautiously, as women who undergo induction of labor in TOLAC have an increased risk of repeat cesarean delivery. Still, success rates with induction are high. Data from the MFMU Cesarean Registry showed that about 66% of women undergoing induction after one prior cesarean delivery achieved VBAC versus 76% of women entering TOLAC spontaneously (Obstet Gynecol. 2007 Feb;109[2 Pt 1]:262-9). Another study of women undergoing induction after one prior cesarean reported an overall success rate of 78% (Obstet Gynecol. 2004 Mar;103[3]:534-8).

Whether induction specifically increases the risk for uterine rupture in TOLAC, compared with expectant management, is unclear. There also are conflicting data as to whether particular induction methods increase this risk.

Based on available data, ACOG considers induction of labor for either maternal or fetal indications to be an option for women undergoing TOLAC. Oxytocin may be used for induction as well as augmentation, but caution should be exercised at higher doses. While there is no clear dosing threshold for increased risk of rupture, research has suggested that higher doses of oxytocin are best avoided.

The use of prostaglandins is more controversial: Based on evidence from several small studies, ACOG concluded in its 2010 bulletin that misoprostol (prostaglandin E₁) for cervical ripening is contraindicated in women undergoing TOLAC. It appears likely that rupture risk increases in patients who received both prostaglandins and oxytocin, so ACOG has advised avoiding their sequential use when prostaglandin E₂ is used. This of course limits the options for the practitioner. Therefore, utilizing a Foley catheter followed by pitocin has been an approach advocated in some cases.

Uterine rupture is not predictable, and it is far more difficult to assess an individual’s risk of this complication than it is to assess the likelihood of VBAC. Still, there is value to discussing with the patient whether there are any other modifiers that could potentially influence the risk of rupture.

Since rates of uterine rupture are highest in women with previous classical or T-shaped incision, for example, it is important to try to ascertain what type of incision was previously used. It is widely appreciated that low-transverse uterine incisions are most favorable, but findings are mixed in regard to low-vertical incisions. Some research shows that women with a previous low-vertical incision do not have significantly lower VBAC success rates or higher risks of uterine rupture. TOLAC should therefore not be ruled out in these cases.

Additionally, TOLAC should not be ruled out for women who have had more than one cesarean delivery. Several studies have shown an increased risk of uterine rupture after two prior cesarean deliveries, compared with one, and one meta-analysis suggested a more than twofold increased risk (BJOG. 2010 Jan;117(1):5-19.).

In contrast, an analysis of the MFMU Cesarean Registry found no significant difference in rupture rates in women with one prior cesarean versus multiple prior cesareans (Obstet Gynecol. 2006 Jul;108[1]:12-20.).

It appears, therefore, that even if having more than one prior cesarean section is associated with an increased risk of rupture, the magnitude of this increase is small.

Just as women with a prior vaginal delivery have the highest chance of VBAC success, they also have the lowest rates of rupture among all women undergoing TOLAC.

Patient counseling

We must inform our patients who have had a cesarean section in the past of their options for childbirth in an unbiased manner.

The complications of both TOLAC and elective repeat cesarean section should be discussed, and every attempt should be made to individually assess both the likelihood of a successful VBAC and the comparative risk of maternal and perinatal morbidity. A shared decision-making process should be adopted, and whenever possible, the patient’s preference should be respected. In the end, a woman undergoing TOLAC should be truly motivated to pursue a trial of labor, because there are inherent risks.

One thing I’ve learned from my clinical practice and research on this issue is that the desire to undergo a vaginal delivery is powerful for some women. Many of my patients have self-referred for consultation about TOLAC after their ob.gyn. informed them that their hospital is not equipped, and they should therefore have a scheduled repeat operation. In many cases they discover that TOLAC is an option if they are willing to travel a half-hour or so.

We need to honor this desire and inform our patients of the option, and help facilitate delivery at another nearby hospital when our own facility is not equipped for TOLAC.

Dr. Landon is the Richard L. Meiling Professor and chairman of the department of obstetrics and gynecology at the Ohio State University, Columbus. He served for more than 25 years as Ohio State’s coinvestigator for the National Institutes of Child Health and Human Development Maternal Fetal Medicine Units Network. He reported having no relevant financial disclosures.