Active labor begins at 6 cm dilation (contemporary Friedman curve). Expected dilation rate: ≥1 cm/hr in active phase (≥6 cm) for nulliparas and multiparas. Arrest of active phase: no cervical change in ≥4 hours with adequate contractions, or ≥6 hours with inadequate contractions. Latent phase prolongation: >20 hours nulliparas, >14 hours multiparas.
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