A 28-year-old multiparous woman at 39 weeks + 2 days gestation with a history of one prior vaginal delivery and one prior caesarean section (for failure to progress) is being counselled for labour induction due to maternal hypertension. Before induction, which investigation is most appropriate to assess cervical readiness and predict the likelihood of vaginal delivery?

## Assessment of Cervical Readiness for Labour Induction ### Clinical Context In a woman with a prior caesarean section being considered for trial of labour after caesarean (TOLAC) with induction, assessment of cervical favourability is essential. A favourable cervix increases the likelihood of successful vaginal delivery and reduces the risk of repeat caesarean section. ### Why Bishop Score is the Investigation of Choice **Key Point:** The Bishop score is the **clinical gold standard** for assessing cervical readiness and predicting the success of labour induction. It is a composite scoring system that is quick, non-invasive, and reproducible. ### Bishop Score Components | Parameter | Score 0 | Score 1 | Score 2 | Score 3 | |---|---|---|---|---| | **Cervical Consistency** | Firm | Medium | Soft | — | | **Cervical Effacement (%)** | 0–30 | 40–50 | 60–70 | 80+ | | **Cervical Dilation (cm)** | 0 | 1–2 | 3–4 | 5+ | | **Cervical Position** | Posterior | Mid | Anterior | — | | **Fetal Station** | −3 | −2 | −1, 0 | +1, +2 | **High-Yield:** - **Bishop score ≥8**: Favourable cervix → induction likely to succeed (vaginal delivery rate ~80%); proceed with oxytocin alone - **Bishop score <6**: Unfavourable cervix → cervical ripening required (misoprostol, dinoprostone, or mechanical methods) before oxytocin - **Bishop score 6–7**: Borderline; consider ripening vs. direct induction based on clinical context **Mnemonic:** **BCDEF** — **B**ody (station), **C**onsistency, **D**ilation, **E**ffacement, **F**orward (position) ### Why Other Options Are Incorrect | Investigation | Role | Why Not First-Line Here | |---|---|---| | **Transvaginal ultrasound (cervical length)** | Research tool; predicts spontaneous preterm birth risk | Not standard for induction readiness; less predictive of induction success than Bishop score | | **Pelvimetry (X-ray/MRI)** | Assesses bony pelvis adequacy | Not indicated in routine induction; relevant only if cephalopelvic disproportion suspected (but this woman had prior vaginal delivery, so adequate pelvis is assumed) | | **Transabdominal ultrasound (fetal weight)** | Estimates fetal size | Does not assess cervical readiness; fetal weight estimation has ±15% error and does not change induction decision in this case | **Clinical Pearl:** In a woman with prior caesarean section (TOLAC candidate), a favourable Bishop score (≥8) is associated with a 60–80% chance of successful vaginal delivery with induction, compared to <20% if the cervix is unfavourable. This guides counselling and decision-making. [cite:Williams Obstetrics 26e Ch 42]