Induction and VBAC: What the Research Says

If you're planning a vaginal birth after cesarean (VBAC) and your care provider has recommended induction, you may find yourself navigating a particularly complex set of questions. Is induction safe with a prior cesarean? How does it affect your chances of achieving a vaginal birth? What methods are safest? And how do you weigh the reasons for induction against the potential risks?

These are important questions, and the answers are not always straightforward. The decision to induce labour in someone with a prior cesarean involves balancing the indication for induction, the method used, and the individual's specific circumstances and goals. In this article, we'll examine what the research tells us about induction during a trial of labour after cesarean (TOLAC), including how it affects both success rates and safety outcomes.

Our goal is to provide you with the evidence you need to have informed conversations with your care provider and to make decisions that align with your values and circumstances.

Why Might Induction Be Recommended?

Before exploring the research on induction and VBAC specifically, it's helpful to understand why induction might be recommended in the first place. Induction is the process of artificially starting labour before it begins on its own, and it may be suggested for a variety of medical and non-medical reasons.

Common medical indications for induction include post-term pregnancy (typically defined as 41 to 42 weeks or beyond), preeclampsia or gestational hypertension, gestational diabetes with concerns about fetal size or glycemic control, prelabor rupture of membranes without spontaneous labor onset, oligohydramnios (low amniotic fluid), intrauterine growth restriction, and certain other conditions that may pose risks to the pregnant person or baby if pregnancy continues.

In some cases, induction may also be offered for non-medical reasons, sometimes called elective induction. This might include scheduling preferences, distance from the hospital, or concerns about precipitous labour. The ARRIVE trial, published in 2018, found that elective induction at 39 weeks in low-risk first-time mothers was associated with a lower cesarean rate compared to expectant management—though this study did not specifically address people with prior cesareans.

When induction is recommended for someone considering TOLAC, the decision becomes more nuanced because induction itself carries implications for both VBAC success and uterine rupture risk.

How Does Induction Affect VBAC Success Rates?

One of the most consistent findings in the research is that spontaneous labour is associated with higher VBAC success rates compared to induced labour. Understanding the magnitude of this difference can help you weigh your options.

The Numbers on Spontaneous Labour

Studies consistently show that people who enter labour spontaneously have VBAC success rates in the range of 70 to 85 per cent, with some studies reporting even higher rates in low-risk populations. Spontaneous labour indicates that the body has initiated the hormonal cascade that supports labour, that the cervix is likely ripening and dilating on its own, and that the conditions for vaginal birth are favourable.

The Numbers on Induced Labour

When labour is induced, VBAC success rates are generally lower—typically in the range of 50 to 70 per cent, depending on the study population and induction method. Some studies have found success rates as low as 50 per cent with induction, while others report rates closer to 65 to 70 per cent. The variation in these numbers reflects differences in patient populations, cervical status at induction, induction methods, and how labour was managed.

A meta-analysis examining TOLAC outcomes found that induction of labour was associated with approximately a 20 to 30 per cent relative reduction in the likelihood of achieving vaginal birth compared to spontaneous labour. In absolute terms, this might translate to a success rate of 75 per cent with spontaneous labour versus 55 to 60 per cent with induction, though individual results vary widely.

Why Does Induction Lower Success Rates?

Several factors may explain the lower success rates associated with induction. First, induction is often performed when the cervix is not yet favourable—meaning it is still long, firm, and closed rather than soft, thin, and beginning to dilate. Inducing labour under these conditions is more difficult and more likely to result in prolonged labour or failure to progress.

Second, induction involves external manipulation of the labour process, which may not align as well with the body's natural rhythms as spontaneous labour. This can result in contractions that are strong but not as effective at dilating the cervix, or in maternal exhaustion from a longer labour process.

Third, induced labour is often subject to time constraints or protocols that may lead to earlier decisions to proceed to cesarean if progress is slow. The management of induced labour may differ from spontaneous labour in ways that influence outcomes.

The Importance of Cervical Status

Research has shown that the Bishop score—a measure of cervical readiness that includes dilation, effacement, station, consistency, and position—is a strong predictor of induction success in all populations, including those attempting VBAC. A favourable Bishop score (typically 6 or higher) is associated with much higher success rates than an unfavourable score.

One study found that VBAC success rates with induction were approximately 67 per cent when the Bishop score was favourable, but only 42 per cent when the cervix was unfavourable. This is a substantial difference and suggests that if induction is being considered, cervical status should be part of the decision-making process.

If your cervix is not yet favourable and induction is not urgently needed, one option may be to wait for spontaneous labour or for the cervix to ripen further. This is a conversation to have with your care provider, weighing the indication for induction against the potential impact on VBAC success.

How Does Induction Affect Uterine Rupture Risk?

Beyond VBAC success rates, the other major consideration with induction during TOLAC is the effect on uterine rupture risk. Research in this area has produced important findings that deserve careful attention.

Overall Rupture Risk with Induction

Multiple studies have found that induction of labour is associated with a higher risk of uterine rupture compared to spontaneous labour. The magnitude of this increase depends on the method of induction used, which we will discuss in detail below.

With spontaneous labour, uterine rupture rates are typically reported at around 0.4 to 0.5 per cent. With induction, rates range from approximately 0.7 per cent to over 2 per cent, depending on the method. This represents roughly a doubling or tripling of the baseline rupture risk in some scenarios.

It is important to keep these numbers in perspective. Even with the increased relative risk, the absolute risk of uterine rupture remains low—less than 2 to 3 per cent even in the highest-risk scenarios. Most induced TOLACs do not result in uterine rupture. However, the increase in risk is meaningful and should be part of the informed consent process.

Prostaglandins and Uterine Rupture

The induction method most strongly associated with increased uterine rupture risk is the use of prostaglandin medications, particularly misoprostol (Cytotec). Prostaglandins are used to ripen the cervix and stimulate contractions, and they are highly effective for this purpose. However, research has consistently shown elevated rupture rates when prostaglandins are used in people with prior cesareans.

A landmark study published in the New England Journal of Medicine in 2001 found that the use of prostaglandins for induction was associated with a uterine rupture rate of approximately 2.4 per cent—roughly five times higher than the 0.4 per cent rate seen with spontaneous labour in the same study. Other studies have found similar or slightly lower rates, but the overall pattern is consistent: prostaglandins are associated with the highest rupture risk among induction methods.

Because of these findings, most professional organisations recommend against the use of misoprostol for cervical ripening or induction in people with prior cesareans. The American College of Obstetricians and Gynaecologists (ACOG) specifically advises avoiding misoprostol in this population due to the increased rupture risk.

Dinoprostone (Cervidil or Prepidil), another prostaglandin, has been less extensively studied in the TOLAC population. Some research suggests that dinoprostone may carry a lower rupture risk than misoprostol, but the evidence is limited, and many providers avoid all prostaglandins for TOLAC induction due to safety concerns.

Oxytocin and Uterine Rupture

Synthetic oxytocin (Pitocin) is the most commonly used agent for inducing or augmenting labour. Its use during TOLAC has been extensively studied, and the findings are more nuanced than with prostaglandins.

Some studies have found a modest increase in uterine rupture risk with oxytocin use, while others have not found a significant independent association after controlling for other factors such as labour duration and cervical status at admission. The relationship may be dose-dependent, with higher doses of oxytocin associated with a greater risk.

One large study found that the rupture rate with oxytocin induction (without prior prostaglandin use) was approximately 0.9 per cent—higher than the 0.4 per cent rate with spontaneous labour but substantially lower than the 2.4 per cent rate seen with prostaglandins. Other studies have reported similar findings, suggesting that oxytocin induction carries an intermediate level of risk between spontaneous labour and prostaglandin induction.

When oxytocin is used during TOLAC, many providers use lower maximum doses and more gradual dose increases compared to protocols for people without uterine scars. Close monitoring for signs of uterine hyperstimulation (contractions that are too frequent or too strong) is standard practice, as hyperstimulation may increase rupture risk.

Mechanical Methods and Uterine Rupture

Mechanical methods of cervical ripening, such as the Foley catheter balloon, have gained attention as potentially safer alternatives for TOLAC induction. These methods work by physically dilating the cervix rather than using medications, and they do not cause uterine contractions directly.

The research on mechanical methods for TOLAC induction is more limited than for pharmacological methods, but the available evidence is generally reassuring. Studies have found that Foley catheter use for cervical ripening in people with prior cesareans does not appear to significantly increase uterine rupture risk compared to spontaneous labour, with rupture rates in the 0.5 to 1 per cent range.

A systematic review examining mechanical methods for TOLAC induction concluded that these methods appear to be safe and effective, with rupture rates similar to those seen with spontaneous labour. However, the authors noted that the total number of cases studied is relatively small, and more research would be valuable.

Because of the favourable safety profile, many providers prefer mechanical methods when cervical ripening is needed for TOLAC induction. Mechanical ripening is often followed by oxytocin once the cervix has become more favourable.

Combination Approaches

In some cases, multiple induction methods may be used in sequence—for example, a Foley catheter followed by oxytocin. The research on combination approaches for TOLAC is limited, but these protocols are commonly used in clinical practice. The overall rupture risk with combination approaches likely depends on the specific methods used, the doses, and the duration of labour.

Comparing the Options: A Summary of the Evidence

To help summarise the research on induction methods and TOLAC outcomes, here is an overview of what the evidence suggests for different approaches.

Spontaneous labour is associated with the highest VBAC success rates, typically 70 to 85 per cent, and the lowest uterine rupture risk, approximately 0.4 to 0.5 per cent. When possible, waiting for spontaneous labour is generally the most favourable scenario for both success and safety.

Mechanical cervical ripening with a Foley catheter appears to have a safety profile similar to spontaneous labour, with rupture rates around 0.5 to 1 per cent. Success rates are lower than with spontaneous labour but are generally better than with other induction methods when the cervix is unfavourable.

Oxytocin induction without prostaglandins is associated with moderately reduced VBAC success rates and a modestly elevated rupture risk of approximately 0.7 to 1 per cent. Careful dosing and monitoring are important.

Prostaglandin induction, particularly with misoprostol, is associated with the highest uterine rupture risk, approximately 2 to 2.5 per cent, and is generally avoided or contraindicated for people with prior cesareans. Dinoprostone may carry a lower risk than misoprostol, but many providers avoid all prostaglandins in this population.

The Decision-Making Process

Given the complexities of induction during TOLAC, how should families and birth workers approach this decision? Several considerations may help guide the conversation.

Understanding the Indication for Induction

The first question to explore is why induction is being recommended. Is there a clear medical indication that makes continuing the pregnancy riskier than proceeding with induction? Or is the indication less urgent, allowing more time for spontaneous labour to occur?

For some conditions, such as severe preeclampsia or significant fetal compromise, the risks of continuing the pregnancy may clearly outweigh the risks of induction. In these cases, induction (or cesarean) may be the safest option regardless of the impact on VBAC success.

For other conditions, such as post-term pregnancy at 41 weeks in an otherwise healthy pregnancy, the calculus may be more nuanced. Some families may choose induction to reduce the small risks associated with prolonged pregnancy, while others may prefer expectant management with close monitoring to optimise their chances of spontaneous labour and VBAC.

Understanding the specific risks of continuing the pregnancy versus the risks of induction can help you make an informed choice. Asking your provider to explain the evidence behind the recommendation, including absolute risk numbers rather than just relative risks, can facilitate this discussion.

Considering Cervical Status

If induction is being considered, assessing cervical readiness is an important step. A cervical exam to determine your Bishop score can provide valuable information about your likelihood of induction success.

If your cervix is favourable, your chances of a successful induced VBAC are much higher than if your cervix is unfavourable. If your cervix is unfavourable and induction is not urgently indicated, you might discuss options such as waiting for spontaneous labour, scheduling a follow-up assessment to see if the cervix has changed, or using membrane sweeping (which some research suggests may help promote spontaneous labour without the risks of formal induction).

Discussing Induction Methods

If induction is appropriate for your situation, discussing the specific methods that will be used is essential. You have the right to understand what agents or techniques are being proposed and to participate in decisions about your care.

For people with prior cesareans, mechanical cervical ripening with a Foley catheter is generally considered the safest option when the cervix is unfavourable. Oxytocin induction is commonly used when the cervix is already favourable or after mechanical ripening. Prostaglandins, particularly misoprostol, should generally be avoided due to the elevated rupture risk.

If your provider recommends a method that you have concerns about, it is appropriate to ask why that method is being chosen, what the alternatives are, and what the risks and benefits of each approach are.

Weighing VBAC Goals Against Other Considerations

For many families, achieving a vaginal birth is an important goal—but it is not the only consideration. The health of the pregnant person and the baby, the indication for induction, and individual risk factors all play a role in the decision.

If the medical indication for induction is strong, the potential reduction in VBAC success rate may be an acceptable trade-off for addressing the underlying concern. If the indication is less urgent, waiting for spontaneous labour may be preferable to optimise VBAC chances.

There is no single right answer. The goal is to make a decision that reflects your values, is informed by the evidence, and is made in partnership with a care provider you trust.

## What If Induction Does Not Lead to Vaginal Birth?

It is important to acknowledge that not all induced TOLACs result in vaginal birth. If induction does not progress as hoped, a cesarean may become necessary. This is not a failure—it is one possible outcome that is part of the informed consent process.

Before beginning induction, it may be helpful to discuss with your care provider what criteria will be used to determine whether labour is progressing adequately, how long induction will be attempted before considering cesarean, and what circumstances would prompt a recommendation for cesarean during the induction process.

Having these conversations in advance can help you understand the decision points that may arise and can reduce uncertainty and distress if the labour does not proceed as hoped.

It is also worth noting that even if an induced TOLAC ends in cesarean, the attempt is not without value. Some families feel that they need to try for a vaginal birth to feel at peace with the outcome. Others may gather information during the attempt that informs future decisions. Each person's experience and perspective are unique.

The Role of Continuous Support

Research consistently shows that continuous labour support—from a doula, partner, or other trained support person—is associated with improved birth outcomes, including higher rates of spontaneous vaginal birth and greater satisfaction with the birth experience. For people attempting VBAC, particularly with induction, this support may be especially valuable.

A doula can provide physical comfort measures, emotional encouragement, and advocacy support throughout the induction and labour process. For families navigating the complexities of induced TOLAC, having a knowledgeable support person can help with coping during what may be a longer labour, with communication with the care team, and with processing the experience afterwards.

If you are considering induction during TOLAC, connecting with a doula or ensuring that you have robust support during labour is worth considering.

Questions to Ask Your Care Provider

If induction is being discussed as part of your TOLAC plan, here are some questions that may help facilitate an informed conversation.

What is the specific indication for induction, and what are the risks of continuing the pregnancy without induction? Understanding why induction is being recommended is the first step.

What is my current cervical status, and how does this affect my likelihood of successful induction? A Bishop score can provide valuable information.

What induction methods do you recommend, and why? Understanding the proposed approach and the rationale behind it is essential.

Will prostaglandins be used? If so, why, and what are the risks? Given the research on prostaglandins and rupture risk, this is an important question to ask.

What are my alternatives if I prefer to wait for spontaneous labour? In some cases, expectant management with close monitoring may be an option.

How will labour be monitored during induction, and what signs will you watch for? Understanding the monitoring plan can help you feel more prepared.

What criteria will be used to determine if the induction is not progressing and a caesarean is recommended? Knowing the decision points in advance can reduce uncertainty.

The Bottom Line

Induction during TOLAC is a complex decision that involves balancing the indication for induction, the method used, and the individual's specific circumstances and goals. The research tells us that induction is associated with lower VBAC success rates compared to spontaneous labour, typically in the range of 50 to 70 per cent versus 70 to 85 per cent with spontaneous labour.

Induction is also associated with a somewhat elevated risk of uterine rupture, though the magnitude of this increase depends heavily on the method used. Prostaglandins, particularly misoprostol, carry the highest rupture risk and are generally avoided or contraindicated for TOLAC. Mechanical methods, such as a Foley catheter, appear to have a safety profile similar to spontaneous labour. Oxytocin induction carries an intermediate level of risk.

Cervical status at the time of induction is a strong predictor of success. A favourable cervix is associated with much higher success rates than an unfavourable cervix.

The decision to proceed with induction during TOLAC should be individualised, taking into account the medical indication, cervical status, available induction methods, and the family's values and priorities. Informed consent requires a clear discussion of the risks, benefits, and alternatives, including the option of expectant management when appropriate.

If induction is recommended for you, asking questions, understanding the evidence, and participating actively in the decision can help ensure that you are making the choice that is right for your unique situation.

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This article is for informational purposes only and does not constitute medical advice. Please consult with your healthcare provider about your individual circumstances and options.