Labor curve and Friedman curve

Labor Curve - The Basic Blueprint

• A graph plotting cervical dilation (cm) vs. time (hours), creating a sigmoid (S-shaped) curve.
• Represents the blueprint for normal labor progression, helping identify deviations.
• Two Major Phases:
  • Latent Phase: Slow, gradual cervical effacement and dilation (up to 6 cm).
  • Active Phase: Rapid, predictable dilation from 6 cm to 10 cm (full dilation).

⭐ Friedman's original criteria are now considered outdated. Modern ACOG guidelines are more lenient, defining active phase arrest as no cervical change for ≥4 hours with adequate contractions or ≥6 hours with inadequate contractions.

Friedman's Curve - The OG Labor Map

• A graph plotting cervical dilation (cm) and fetal station against time, historically used to define normal labor progression.
• Helps identify labor abnormalities like arrest or protraction by comparing the patient's progress to an idealized curve.

• Classic Friedman Thresholds for Adequate Progress:
  • Active Phase Dilation:
    • Nulliparous: ≥1.2 cm/hr
    • Multiparous: ≥1.5 cm/hr
  • Second Stage Fetal Descent:
    • Nulliparous: ≥1 cm/hr
    • Multiparous: ≥2 cm/hr

⭐ Contemporary research (e.g., Zhang et al. data) indicates that labor progression is often slower than Friedman's original estimates, leading to revised, less interventional labor management guidelines.

Labor Dystocia - Detours & Delays

• Definition: Abnormal, slow progression of labor. Diagnosed using Friedman's curve, which plots cervical dilation against time.
• Etiology (The 3 P's):
  • Powers: Inadequate uterine contractions (<200 Montevideo units). Most common cause of dystocia.
  • Passenger: Fetal factors like macrosomia, malpresentation (e.g., breech), or malposition (e.g., occiput posterior).
  • Passage: Pelvic structure abnormalities (e.g., contracted pelvis).

⭐ High-Yield: The most common reason for active phase arrest is inadequate uterine contractions (Powers), assuming cephalopelvic disproportion has been ruled out.

Modern Curves (Zhang) - The New Rules

• Based on modern, larger, and more diverse patient cohorts.
• Key Change: Active labor is now considered to start at 6 cm dilation, not 4 cm.
• Progression from 4 cm to 6 cm is often much slower than previously expected.
• Active Phase Arrest Criteria:
  • No cervical change for ≥ 4 hours with adequate contractions.
  • No cervical change for ≥ 6 hours with inadequate contractions.

⭐ Redefining the start of active labor to 6 cm is the critical update, aimed at reducing cesarean deliveries for arrest of labor.

High‑Yield Points - ⚡ Biggest Takeaways

• Friedman's curve is an older model; modern labor curves (e.g., Zhang) accept a slower progression.
• Prolonged latent phase is >20 hrs (nulliparous) or >14 hrs (multiparous); manage with therapeutic rest.
• Active phase protraction is slow dilation: <1.2 cm/hr (nulliparous) or <1.5 cm/hr (multiparous).
• Active phase arrest is no change for ≥4 hrs with adequate contractions, often requiring C-section.
• Adequate contractions are typically >200 Montevideo units (MVUs).
• Second stage arrest involves pushing with no descent for >3-4 hrs (nulliparous) or >2-3 hrs (multiparous).