A multigravida at 41+2 weeks has a favourable cervix (Bishop score 7). Oxytocin induction is started. After 8 hours of regular uterine contractions, she remains at 4 cm cervical dilatation. CTG shows a normal pattern. Per ACOG/RCOG active phase dystocia criteria, the minimum duration of adequate (>200 Montevideo units) contractions in the active phase before labelling as arrested active phase is:
- A 2 hours
- B 6 hours
- C 4 hours ✓
- D 1 hour
Correct answer: C. 4 hours
Explanation
ACOG (2014) revised criteria define arrested active phase as failure to progress after at least 4 hours of adequate uterine activity (>200 Montevideo units) or 6 hours of inadequate contractions in the presence of membrane rupture and oxytocin. This extended the earlier 2-hour criterion significantly, aiming to reduce unnecessary caesarean sections. The active phase is now not considered to begin until 6 cm dilation (new threshold), further reducing premature intervention.
Reference: Williams Obstetrics, 26th ed.
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Written and medically reviewed by the StethoPrep medical team.