Management of Primigravida at 5 cm Dilation After 4 Hours
The correct next step is to wait and continue monitoring, as this patient does not meet criteria for active phase arrest—she is likely still in late latent phase or early active phase, and 4 hours without change at 5 cm does not constitute an arrest disorder. 1
Understanding the Active Phase Definition Controversy
The question highlights a critical debate in modern obstetrics regarding when active labor truly begins:
- Modern guidelines (ACOG/WHO) define active phase as beginning at ≥6 cm dilation, not at 4-5 cm as older Friedman criteria suggested 1, 2
- At 5 cm dilation, this patient is technically still in latent labor according to current evidence-based definitions 1
- The active phase can begin at variable cervical dilations, but many nulliparas don't enter true active phase until after 5-6 cm 1, 3
Why This Is NOT Active Phase Arrest
Active phase arrest requires BOTH:
- Being in confirmed active phase (≥6 cm dilation) 4, 2, 5
- No cervical change for ≥4 hours with adequate contractions (or ≥6 hours without adequate contractions) 1, 4, 5
This patient fails criterion #1—she has not yet reached active phase. At 5 cm, she may still be progressing through late latent phase, where slower progression is physiologically normal 1, 3
The Danger of Premature Intervention
Intervening too early at 5 cm carries significant risks:
- Cesarean section at this stage is inappropriate because labor abnormalities (arrest/protraction) can only be diagnosed in active labor (≥6 cm) 2
- Oxytocin augmentation before confirmed active phase increases the risk of unnecessary interventions and may lead to cascade effects including cesarean delivery 2
- Amniotomy is contraindicated in latent labor and should only be performed in active labor (≥6 cm) when documented dystocia exists 2
Recommended Management Algorithm
Step 1: Continue expectant management with close monitoring 1
- The CTG is reassuring, indicating no fetal compromise
- Serial cervical examinations should be performed to document progression
- Wait for the patient to reach 6 cm dilation before diagnosing any labor abnormality 1, 2
Step 2: Reassess at 6 cm or beyond 1, 4
- If she reaches 6 cm and then has no cervical change for 4 hours with adequate contractions, then active phase arrest can be diagnosed 1, 4, 5
- At that point, evaluate for cephalopelvic disproportion (CPD), which occurs in 25-30% of active phase arrest cases 1, 4, 6
Step 3: If active phase arrest is confirmed at ≥6 cm 1, 4
- If CPD is ruled out: Oxytocin augmentation is first-line treatment with 92% success rate for vaginal delivery 4
- If CPD is present or suspected: Cesarean delivery is indicated, as oxytocin is contraindicated 6
Critical Pitfalls to Avoid
- Do not diagnose "active phase arrest" before 6 cm dilation—this leads to unnecessary cesarean deliveries 1, 2
- Do not perform amniotomy in latent labor—this increases infection risk and commits the patient to delivery within 24 hours 2
- Do not rush to cesarean section without documenting true labor abnormality—half of cesarean deliveries for "active phase dystocia" in one study had normal dilation curves, suggesting diagnostic error 1
Evidence Quality Note
The 2023 American Journal of Obstetrics and Gynecology expert opinion by Cohen and Friedman provides the most recent, comprehensive analysis of this controversy 1. They demonstrate that the Zhang et al. methodology (which formed the basis for the 6 cm cutoff) had significant methodological flaws including selection bias and interval-censored regression errors 1. However, the clinical consensus remains that 6 cm is the safer threshold for defining active phase to avoid premature intervention 1, 2.
Answer: C - Wait for 2 more hours (and continue monitoring until she reaches at least 6 cm before considering any intervention)