Target: 3-4 contractions per 10 minutes, each lasting 40-50 seconds in the active phase.
Tachysystole Alert
> 5 contractions per 10 mins (Averaged over 30 mins)
The World Health Organization (WHO) has replaced the traditional 4-hour action line with a 1cm per 2-hour action limit to reduce unnecessary interventions.
Guidelines & Evidence
Clinical Details
Section 1
When to Use
Primary Clinical Uses
Continuous monitoring of intrapartum maternal and fetal well-being.
Identifying prolonged or obstructed active labor to trigger interventions (amniotomy, oxytocin, cesarean).
Completely replacing the legacy 1950s Friedman Curve and the outdated WHO Partograph.
The Paradigm Shift
The rigid "1 cm per hour" rule is dead. Modern evidence shows that physiological labor is entirely non-linear. The WHO Labour Care Guide (LCG) dictates that active labor does not begin until 5 cm of dilation, and allows for significantly slower early progress without intervening.
Section 2
Formula & Logic
Defining Active Phase
Latent phase continues until 5 cm of cervical dilation. The active phase is strictly defined as 5 cm to 10 cm. Interventions to accelerate labor should NOT routinely be performed before 5 cm.
Dynamic Alert Thresholds
5 cm to 6 cm
May take up to 6.0 hours (Nullip/Multip)
6 cm to 7 cm
May take up to 3.0 hours (Nullip) / 2.5 hours (Multip)
7 cm to 8 cm
May take up to 2.5 hours (Nullip) / 2.0 hours (Multip)
8 cm to 10 cm
Accelerates; usually < 2 hours.
Section 3
Pearls/Pitfalls
Key Nuances
Do not routinely perform amniotomy (breaking the water) or start Oxytocin just because the latent phase (< 5cm) is prolonged, provided maternal/fetal signs are stable.
ACOG guidelines (US) differ slightly by defining the onset of the active phase at 6 cm, structurally allowing even more conservative management in the 4-5 cm window compared to the global WHO 5 cm rule.
Epidural analgesia routinely adds 1-2 hours to the active phase; thresholds must be mentally adjusted.
Section 4
Next Steps
Triggering Interventions
01
Progress crosses the established maximum time limit for the specific centimeter increment.
02
Perform thorough assessment of the 3 P's: Power (contractions), Passenger (fetal position/size), Pelvis.
03
If contractions are inadequate: Consider Artificial Rupture of Membranes (AROM) and Oxytocin augmentation.
04
If adequate contractions (>200 Montevideo units) persist for 4 hours with no cervical change in the active phase: Arrest of active labor. Proceed with Cesarean delivery.
Section 5
Evidence Appraisal
WHO Guidelines
WHO recommendations: intrapartum care for a positive childbirth experience.
World Health Organization. • Geneva: WHO.. 2018;The landmark guideline that formally abandoned the 1 cm/hour Friedman curve and redefined the active phase to 5 cm.
Contemporary patterns of spontaneous labor with normal neonatal outcomes.
Zhang J et al. • Obstet Gynecol.. 2010;The original US consortium study proving that the cervix dilates at an exponential (not linear) curve, fundamentally altering obstetrical practice worldwide.
Section 6
Literature
Emanuel Friedman
In 1955, Dr. Emanuel Friedman studied 500 women and created the "Friedman Curve." For 60 years, it was undisputed dogma. However, modern women are older, have higher BMIs, larger babies, and widely use epidurals, rendering the 1950s data highly dangerously inaccurate and triggering an epidemic of premature cesarean deliveries.
