A 32-year-old multiparous woman at 40 weeks + 5 days gestation is admitted for induction of labor due to post-term pregnancy. Cervical examination reveals a Bishop score of 9 (2 cm dilation, 80% effaced, soft cervix, anterior position, −1 station). Fetal heart rate is reassuring. Oxytocin infusion is initiated at 2 mIU/min and increased by 2 mIU/min every 40 minutes. After 6 hours of augmentation, the patient is in active labor with contractions every 2–3 minutes. However, cervical dilation has plateaued at 6 cm for the past 2 hours, and the fetal head remains at −1 station. What is the most appropriate next step in management?

Explanation

## Clinical Scenario Analysis The patient is in **active phase arrest** (cervical dilation plateau at 6 cm for ≥2 hours despite adequate contractions). The next step depends on membrane status and the adequacy of uterine contractions. ## Diagnosis: Active Phase Arrest **Key Point:** Active phase arrest is defined as: - Cervical dilation ≥4 cm - Adequate contractions (≥200 Montevideo units over 10 minutes OR ≥5 contractions in 10 minutes) - No cervical change for ≥2–4 hours In this case: - Dilation plateaued at 6 cm for 2 hours ✓ - Contractions every 2–3 minutes (adequate frequency) ✓ - Fetal heart rate reassuring ✓ ## Management Algorithm for Active Phase Arrest ```mermaid flowchart TD A[Active Phase Arrest]:::outcome --> B{Membranes ruptured?}:::decision B -->|No| C[Perform ARM]:::action B -->|Yes| D{Adequate contractions?}:::decision C --> E[Reassess in 2 hours] D -->|No| F[Increase oxytocin]:::action D -->|Yes| G[Consider cesarean delivery]:::action E --> H{Progress?}:::decision H -->|Yes| I[Continue labor]:::outcome H -->|No| J[Cesarean delivery]:::urgent ``` ## Why ARM First? **High-Yield:** Artificial rupture of membranes (ARM) is performed BEFORE escalating oxytocin or considering cesarean delivery because: 1. **Removes barrier to descent**: Intact membranes can impede fetal descent and cervical dilation 2. **Allows direct assessment**: Enables visualization of amniotic fluid color (meconium staining) and fetal scalp condition 3. **Enhances contraction efficiency**: Increases intrauterine pressure transmission to the cervix 4. **Non-invasive escalation**: Less morbid than increasing oxytocin further or surgical delivery **Clinical Pearl:** In a multiparous woman with adequate contractions and an unfavorable fetal station (−1), ARM often resolves arrest and allows spontaneous vaginal delivery. ## Oxytocin Status The patient is already on a reasonable oxytocin dose (likely 10–12 mIU/min after 6 hours of incremental increases). Further escalation without ARM is less likely to be effective and increases the risk of uterine hyperstimulation. ## Why Not Cesarean Delivery Yet? **Warning:** Cesarean delivery for arrest disorder should only be performed after: - ARM (if membranes intact) - Adequate oxytocin augmentation (≥18–20 mIU/min for ≥2 hours) - Reassessment of progress Premature cesarean delivery increases maternal morbidity without improving fetal outcomes in this scenario.