The Friedman labour curve was re-examined by Zhang et al. (2010). What key finding from the Zhang curve changed the management of labour dystocia in modern obstetrics?
- A Active phase does not begin until 6 cm dilation in contemporary obstetric populations ✓
- B Active phase begins at 3 cm and progression is 1.2 cm/hr in nulliparas
- C The second stage limit for nulliparas should remain 2 hours without regional analgesia
- D Latent phase duration over 20 hours is abnormal in nulliparas
Explanation
The landmark Zhang et al. (2010) re-analysis of the Consortium on Safe Labour dataset (62,000+ deliveries) demonstrated that the active phase of labour (with its more rapid cervical dilation) does not reliably begin until 6 cm in modern, typically obese, and older obstetric populations. This contrasted with Friedman's original definition of active phase at 3–4 cm. Consequently, ACOG/SMFM 2014 revised labour guidelines recommend not diagnosing labour dystocia in the active phase until ≥6 cm is reached with ≥4 hours of inadequate contractions or ≥6 hours of adequate contractions with no progress.
Reference: Williams Obstetrics, 26th ed.
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