How is a labor curve created?

How a Labor Curve is Created

A labor curve is created by plotting serial measurements of cervical dilatation and fetal station against time in labor, documenting the rate of progress in centimeters per hour to identify normal versus abnormal labor patterns. 1

Components of a Labor Curve

• Cervical Dilatation: Measured in centimeters (0-10 cm) and plotted on the y-axis
• Time: Measured in hours from admission or onset of active labor and plotted on the x-axis
• Fetal Station: Descent of the fetal presenting part through the birth canal
• Additional Parameters: Maternal vital signs, fetal heart rate, uterine contractions, and interventions

Normal Labor Progress Parameters

• Nulliparous women: Cervical dilatation should progress at ≥1.2 cm/h during active phase 2, 1
• Multiparous women: Cervical dilatation should progress at ≥1.5 cm/h during active phase 2, 1

Identifying Labor Phases on the Curve

The labor curve typically demonstrates:

1. Latent Phase:

   • Slow cervical change
   • May extend to various dilatations (not fixed at a specific centimeter)
   • Characterized by slower rate of dilatation

2. Active Phase:

   • Begins with an inflection point showing acceleration in the rate of dilatation
   • Identified by a change in rate from the latent phase
   • Can occur at various cervical dilatations, not necessarily at a fixed point 2
   • Most recent evidence suggests this typically occurs between 5-6 cm 3

3. Deceleration Phase:

   • Near complete dilatation
   • Rate may slow slightly before full dilatation

Creating an Accurate Labor Curve

1. Perform serial cervical examinations:

   • Document cervical dilatation, effacement, and fetal station
   • Record the exact time of each examination

2. Plot measurements on a partogram:

   • Mark cervical dilatation on the y-axis
   • Mark time in labor on the x-axis
   • Connect the points to visualize the rate of progress

3. Document additional parameters:

   • Fetal heart rate: Every 15-30 minutes during active phase 1
   • Uterine contractions: Frequency, duration, and intensity 1
   • Maternal vital signs
   • Interventions (oxytocin, analgesia, position changes)

Identifying Abnormal Labor Patterns

The labor curve helps identify:

1. Protracted Active Phase:

   • Nulliparas: <1.2 cm/h for >2-3 hours 2, 1
   • Multiparas: <1.5 cm/h for >1 hour 2, 1

2. Arrest of Active Phase:

   • No cervical change for 2 hours 2, 1

Common Pitfalls in Labor Curve Creation

• Incorrect identification of labor phase: Failing to recognize the transition from latent to active phase 2, 1
• Relying solely on time-based assessments: Modern research shows that multifactor models incorporating previous examination findings, contraction patterns, and other clinical parameters provide more accurate predictions of labor progress 4
• Inconsistent examination technique: Different examiners may assess cervical dilatation differently, leading to inconsistencies in the curve
• Inadequate frequency of examinations: Too few data points can result in an inaccurate representation of labor progress

Modern Advances in Labor Curve Creation

Recent research has demonstrated that:

• Labor curves based on multiple clinical parameters show improved prediction accuracy compared to models based on time alone 4
• Machine learning methods can reduce prediction errors by more than 50% compared to traditional time-based models 4
• Individual labor patterns show wide variation, and most labors do not follow an average dilatation curve 5

By accurately creating and interpreting labor curves, clinicians can better identify abnormal labor patterns, make appropriate interventions, and potentially reduce unnecessary cesarean deliveries while improving maternal and fetal outcomes.