The Maternal Fetal Medicine Unit (MFMU) Network defined a novel labour curve (Zhang curve) in 2010 that contrasts with the classic Friedman curve. Which is the most clinically significant difference between the two?
- A The Friedman curve identified 4 cm as the transition to active phase; the Zhang curve shifts this to 6 cm ✓
- B The Zhang curve shows faster cervical progress than Friedman's in active phase
- C The Friedman curve is based on epidural analgesia use; Zhang curve is not
- D The Zhang curve applies only to multiparous women
Explanation
The Zhang curve (2010) from the MFMU Network — based on 62,415 vaginal deliveries — showed that labour in the contemporary obstetric population progresses differently from Friedman's 1955 cohort: the transition to a steep active phase does not reliably occur at 4 cm but rather at 6 cm. Below 6 cm, labour may be slow even in normal cases. This led ACOG (2014) to revise the definition of active phase to ≥6 cm, significantly reducing 'failure to progress' diagnoses and unnecessary caesarean sections. The Friedman and Zhang curves both include women with and without epidurals in their respective analyses.
Reference: Williams Obstetrics, 26th ed.
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Written and medically reviewed by the StethoPrep medical team.