In which clinical scenario is a trial of labour after a previous cesarean section (CS) most likely to succeed in achieving a vaginal birth?

Trial of Labor After Cesarean: Likelihood of Success in Different Clinical Scenarios

Previous CS for breech presentation with spontaneous labor at term in the current pregnancy is most likely to succeed in achieving a vaginal birth.

Factors Affecting TOLAC Success

According to the American Academy of Family Physicians (AAFP) guidelines, approximately 74% of women who attempt labor after cesarean have a successful vaginal birth 1, 2. However, several factors significantly influence the likelihood of success:

Positive Predictors of VBAC Success

• Previous vaginal birth (strongest clinical predictor)
• Spontaneous labor (vs. induction)
• Higher Bishop scores (indicating favorable cervix)
• Non-recurrent indication for previous cesarean
• Normal progression of labor

Negative Predictors of VBAC Success

• Labor induction, especially with unfavorable cervix
• Low Bishop score
• Previous cesarean for failure to progress/labor dystocia
• Maternal obesity
• Macrosomia (≥4,000g)
• Recurrent indication for cesarean

Analysis of the Clinical Scenarios

1. Previous CS for breech presentation, spontaneous labor at term

   • Non-recurrent indication (breech)
   • Spontaneous labor (not induced)
   • Term gestation (favorable)

2. Previous CS for twins, Bishop's score of 3 at 41 weeks

   • Non-recurrent indication (twins)
   • Unfavorable cervix (Bishop score of 3)
   • Post-term pregnancy requiring induction

3. Previous CS for breech, induction for gestational hypertension at 38 weeks

   • Non-recurrent indication (breech)
   • Need for induction (decreases success)
   • Medical complication (gestational hypertension)

4. Previous CS for failure to progress, spontaneous labor at term

   • Recurrent indication (failure to progress)
   • Spontaneous labor (favorable)
   • Term gestation (favorable)

Risk Considerations

The AAFP guidelines note that labor induction is associated with higher rates of uterine rupture 1:

• Oxytocin: 1.1% risk
• Prostaglandin E2: 2% risk
• Misoprostol: 13% risk (contraindicated in TOLAC)

An unfavorable cervix (low Bishop score) significantly reduces the likelihood of successful VBAC, especially when induction is required 2.

Conclusion

The scenario with the highest likelihood of success is previous CS for breech presentation with spontaneous labor at term in the current pregnancy because:

• The previous cesarean was for a non-recurrent indication (breech)
• Current labor is spontaneous (not induced)
• No medical complications requiring intervention
• Term gestation with likely favorable cervical conditions

The scenario with previous CS for failure to progress has a lower success rate due to the recurrent nature of the indication, which suggests an underlying anatomical or physiological factor that may persist in subsequent pregnancies 1, 2. The scenarios requiring induction, especially with an unfavorable Bishop score, have significantly reduced chances of successful VBAC.