Trial of Labour and Trial of Scar

The dictum “Once a caesarean always a caesarean” has largely permeated the obstetric practice for most of the twentieth century and today the term Vaginal Birth After Caesarean (VBAC) refers to delivery of an infant through the vagina in a female who has had a prior cesarean section.

So, in reality VBAC is “the desirable outcome” and not an intervention/or practice.

Since VBAC is the outcome, the practice or interventions are now been referred to as “trial of labour after previous caesarean delivery” (TOLAC).

So patients desiring VBAC delivery undergo a TOLAC.

Therefore, TOLAC provides women who had a prior caesarean with an opportunity to achieve a vaginal birth after caesarean

However VBAC and TOLAC are sometimes used synonymously.

The term VBAC was introduced in 1991 and the practice was endorsed by both the NIH and the WHO through consensus meetings in the 1980s as a strategy to reduce the rising caesarean delivery rates seen in the 1970s and 1980s.

Since then, the incidence of VBAC has increased from 5% in 1985 to 28.3% in 1996.

Individual level: lower risk of maternal morbidity and fewer complications in future pregnancies.

Population level: overall decrease in caesarean delivery.

However, either elective repeat caesarean delivery (ERCD) or TOLAC have associated risk and medical decision making should be guided by evidence with patient engagement in understanding the associated risk.

Risks to consider:

• Uterine scar dehiscence or rupture
• Maternal and neonatal morbidity or mortality
• Medico-legal liability

Considerations for future pregnancies and the impact of repeat/multiple caesarean sections are critical:

• Risk of hysterectomy increases with each additional caesarean delivery.
• Placenta previa: risk of placenta previa increases with each additional caesarean delivery.
• Placenta accreta: risk of accreta increases significantly after 2 or more prior caesarean deliveries.

This implies that future morbidity are significantly higher with repeated caesarean sections.

Risk of maternal death is higher for ERCD at 13.4 per 100,000 compared to 3.8 per 100,000 TOLAC.

Who are the ideal candidates for TOLAC/VBAC?

ACOG recent practice bulletin on VBAC recommended that “most women with one previous CS with a low transverse incision are candidates for and should be counseled about VBAC and offered TOLAC”

The strongest predictors of VBAC are:

• Previous vaginal delivery prior to CS predicts about 83% success of VBAC.
• Prior VBAC predicts subsequent success of VBAC by 94%.
• There is a positive correlation between number of prior VBACs and the likelihood of achieving VBAC in the current pregnancy:
• 0 (63%)
• 1 (87.6%)
• 2 (90.9%)
• 3 or more (90.6-91.6%)
• Nonrecurring indications such as fetal distress, malpresentation positively predicts success
• Previous CS was indicated by cephalopelvic disproportion, failure to progress/active phase arrest, labor dystocia, arrest of descent, the likelihood of achieving VBAC was 54% (48-60%).
• Estimated fetal weight ≥4.0kg reduces odds of achieving VBAC by 39-51% relative to women with smaller babies.
• As gestational age increases the likelihood of VBAC decreases particularly when pregnancy progresses beyond 41 weeks.

The following factors are associated with lower likelihood of achieving success in VBAC:

• Race/ethnicity (Hispanic and African American compared to non-Hispanic whites)
• Increase in maternal age
• Increased maternal BMI at first antenatal visit or at delivery
• Pre-existing maternal medical disease
• Short interdelivery interval (< 18 mo)
• Prolonged gestation > 41 wk

Intrapartum factors associated with VBAC:

• Pregnancies requiring induction or augmentation of labor have a lower likelihood for successful VBAC (range 61-69%); odds ratio=0.52 (CI: 0.33-0.82).
• Cervical status at admission and VBAC: advanced cervical dilatation > 4cm, advanced effacement, in spontaneous labor increases the likelihood of achieving VBAC by 2 fold (OR=2.2; CI: 1.7-2.8).

• Non-clinical interventions
• Elective repeat CS vs Induction of labor in a previous CS birth
• VBAC for 2 previous CS

Non-clinical interventions:

Summary of evidence

The following interventions reduced intrapartum caesarean section rates:

• Implementation of evidence-based guidelines/protocols
• Mandatory second opinion before caesarean sections
• The following interventions reduced repeat caesarean section rates:
• Peer review including pre-caesarean consultation
• Mandatory second opinion and post caesarean surveillance
• Guidelines disseminated with endorsement and support of local opinion leaders may increase the proportion of women with previous CS being offered TOLAC in certain setting.
• Nurse-led relaxation classes and birth preparation classes may reduce CS rates in low-risk pregnancies

Elective repeat CS vs Induction of labor in a previous CS birth:

Summary of evidence

• Current evidence for decision for elective repeat caesarean section or induction of labor in a woman with a previous CS delivery are limited to non-randomized studies.
• Both interventions are associated with benefits and harms.
• A policy of shared decision making between the obstetrician and the patient/family preferences and priorities should guide appropriate actions in such clinical scenario.

VBAC for 2 previous CS:

How successful is VBAC-2 compared to VBAC-1 or VBAC-2 vs repeat CS?

Summary of evidence

• Overall success rate for VBAC-2 was 71.1% (45%-89%) compared to VBAC-1-76.5%; a significant difference between the 2 groups (OR=1.48).
• Uterine rupture was significantly reduced by 58% in women who had VBAC-1 compared to women in the VBAC-2 group, OR=0.42

Rates of hysterectomy in VBAC-2 vs repeat 3 CS:

Summary of evidence

• Success rate in VBAC-2 is reasonably high at 71.1%
• Uterine rupture is 1.36%, significantly higher than VBAC-1 at 0.72%
• Maternal morbidities are comparable with repeat 3-CS option
• No significant differences in neonatal outcomes compared to VBAC-1 or repeat 3-CS option
• Women requesting this option should be so counseled

Once a Caesarean is an opportunity to consider the option for vaginal birth.

In terms of risk of maternal death, vaginal delivery is safer compared to repeat caesarean.

Implementation of evidence-based protocol for VBAC, with second opinion could significantly reduce repeat caesarean section rates.

A previous caesarean requiring induction of labor in index pregnancy has a lower likelihood for successful VBAC.

Patient education and shared decision making is required in choosing the optimal decision path in specific clinical scenarios for VBAC.

The success rate for VBAC-2 is reasonably high (71%) and there is growing evidence to support the practice.