5.2 The First and Second Stages of Labor
Key Takeaways
- The active phase begins at 6 cm, and active-phase arrest requires 6 cm or more with ruptured membranes plus either 4 hours of adequate contractions at 200 Montevideo units or more, or 6 hours of oxytocin with inadequate contractions.
- A prolonged latent phase, defined as more than 20 hours in a nullipara or 14 hours in a multipara, is not by itself an indication for cesarean birth.
- Passive descent for 1 to 2 hours in patients with neuraxial analgesia and no urge to push reduces operative vaginal birth and severe perineal laceration.
- Directed closed-glottis Valsalva pushing lowers maternal venous return and intervillous flow and increases fetal acidemia compared with spontaneous open-glottis pushing.
- Squatting increases the functional interspinous and intertuberous diameters of the pelvic outlet by roughly 20 to 30 percent.
Last updated: September 2026
The First Stage of Labor
First Stage of Labor (Onset of Regular Contractions to Complete 10 cm Dilation)
The first stage encompasses the entire dilatation of the cervix and is divided into two distinct physiological phases:
- Latent Phase (0 to 5 cm): Characterized by slow, gradual cervical softening, effacement, and early dilation. Contractions coordinate from irregular twinges into regular rhythmic cycles. The duration of the latent phase is highly variable. Per modern ACOG/SMFM guidelines, a prolonged latent phase is defined as >20 hours in a nullipara and >14 hours in a multipara. A prolonged latent phase alone is not an indication for cesarean delivery, as the vast majority of women with prolonged latent phase will safely enter the active phase with expectant management, supportive care, hydration, or therapeutic rest (e.g., morphine sleep).
- Active Phase (6 cm to 10 cm): Begins at 6 cm cervical dilation, characterized by rapid cervical dilation and accelerated fetal descent.
The Paradigm Shift: Historical Friedman Curve vs. Modern Zhang Labor Curve
For decades, obstetric practice relied on Emanuel Friedman's 1954 labor curve, which established an inflection point for active labor at 4 cm dilation and dictated that nulliparas dilate at a minimum rate of 1.2 cm/hr and multiparas at 1.5 cm/hr. Failure to achieve these benchmarks historically resulted in rapid diagnoses of "failure to progress" and high rates of primary cesarean delivery.
In 2010, the Consortium on Safe Labor (Zhang et al.) published contemporary multi-center data demonstrating that modern labor progression is substantially slower before 6 cm:
- Cervical dilation follows a hyperbolic curve rather than a sigmoid curve.
- Labor may take more than 6 hours to progress from 4 cm to 5 cm, and over 3 hours to progress from 5 cm to 6 cm in normal nulliparous women.
- Dilation accelerates consistently only once the cervix reaches 6 cm.
| Clinical Metric | Friedman Curve (1954 Historical) | Zhang / Consortium on Safe Labor (Modern Standard) |
|---|---|---|
| Active Phase Threshold | 4 cm cervical dilation | 6 cm cervical dilation |
| Active Dilation Rate (Nullipara) | ≥ 1.2 cm/hour | Slower prior to 6 cm; highly variable (0.5 to 1.0+ cm/hr) |
| Active Dilation Rate (Multipara) | ≥ 1.5 cm/hour | Slower prior to 6 cm; accelerates after 6 cm |
| Active Phase Protraction | Dilation slower than minimum slope | Slower than expected rate, but progressing without signs of arrest |
| Diagnostic Criteria for Active Phase Arrest | Failure to dilate for ≥ 2 hours past 4 cm | Cervical dilation ≥ 6 cm with ruptured membranes and:<br/>• ≥ 4 hours of adequate contractions (≥ 200 MVUs), OR<br/>• ≥ 6 hours of oxytocin with inadequate contractions |
Cervical Assessment & The Bishop Score
Cervical evaluation involves five physical parameters scored from 0 to 2 or 3:
- Dilation: Diameter of internal cervical os (0 to 10 cm).
- Effacement: Degree of cervical thinning from an uneffaced 3–4 cm tubular structure (0%) to a paper-thin rim (100%).
- Station: The relationship of the leading bony part of the fetal presenting part to the maternal ischial spines (station 0 corresponds to the level of the spines; station -5 to -1 indicates centimeters above the spines; station +1 to +5 indicates centimeters below the spines towards the introitus).
- Consistency: Cervical tissue texture (firm, medium, or soft).
- Position: Spatial orientation of the cervical os relative to the fetal head (posterior, midposition, or anterior).
The Second Stage of Labor
Second Stage of Labor (Complete 10 cm Dilation to Expulsion of the Infant)
The second stage represents the phase of active fetal expulsion. Management principles include:
- Passive Descent ("Laboring Down"): In women with regional analgesia who lack an immediate spontaneous urge to push, allowing 1 to 2 hours of passive descent under the influence of uterine contractions alone promotes spontaneous fetal rotation, reduces maternal exhaustion, lowers the incidence of operative vaginal delivery, and reduces severe perineal lacerations.
- Physiological Spontaneous Pushing (Open-Glottis) vs. Directed Pushing (Valsalva / Closed-Glottis):
- Spontaneous Open-Glottis Pushing: The laboring woman bears down instinctively for 5 to 7 seconds per effort, releasing air and vocalizing during exhalation. This maintains intrathoracic pressure equilibrium, preserves maternal venous return, stabilizes blood pressure, and optimizes continuous oxygen delivery to the placental bed.
- Directed Closed-Glottis Pushing: Coached sustained bearing down while holding the breath (Valsalva maneuver) for 10 seconds or longer. This sharply elevates maternal intrathoracic pressure, decreases cardiac venous return, triggers a rebound drop in maternal arterial blood pressure, diminishes intervillous blood flow, and significantly increases fetal acidemia, while predisposing the maternal pelvic floor to denervation and muscular avulsion.
- Maternal Birth Positioning:
- Upright / Standing / Walking: Utilizes gravity to accelerate descent, improves contraction alignment, and facilitates pelvic angle adjustment.
- Squatting: Maximizes the functional dimensions of the pelvic outlet, increasing the interspinous and intertuberous diameters by up to 20% to 30%.
- Hands-and-Knees (All-Fours): Excellent for alleviating persistent lumbosacral pain ("back labor"), facilitating spontaneous rotation of persistent occiput posterior (OP) or occiput transverse (OT) fetuses, and relieving pressure on the maternal perineum.
- Lateral Sims / Side-Lying: Provides high perineal control, reduces rapid crowning, minimizes pelvic floor tension, and optimizes uteroplacental perfusion by relieving aortocaval compression.
- Peripartum Perineal Support: The CNM applies warm compresses to the perineum during the second stage to enhance tissue vascularity and elasticity, performs gentle perineal massage with water-soluble or organic lubricant, and utilizes a "hands-poised" or gentle "hands-on" approach (gentle digital support of the crowning vertex to promote slow extension and prevent rapid explosive expulsion).
Test Your Knowledge
A 24-year-old primigravida at 39 weeks gestation presents to the labor and delivery unit reporting regular, painful contractions every 4 minutes. Initial cervical examination reveals 4 cm dilation, 80% effacement, and -1 station. Four hours later, a repeat digital examination demonstrates 5 cm dilation, 90% effacement, and -1 station. Maternal vital signs and electronic fetal monitoring are reassuring (Category I). The obstetrical resident recommends proceeding with a primary cesarean delivery for active phase arrest. What is the most appropriate, evidence-based midwifery management?
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D