Active Labor: Definition and Management
Active labor begins when cervical dilation accelerates from the flat slope of latent phase to a more rapid progression, identified through serial vaginal examinations at least every 2 hours, regardless of the specific centimeter of dilation achieved. 1, 2
Definition of Active Phase
The onset of active labor is determined solely by an accelerating rate of cervical dilation, not by a specific centimeter threshold. 1 This represents a critical shift from traditional teaching:
- Active phase begins at various degrees of dilation when the rate transitions from the relatively flat slope of latent phase to more rapid progression 1
- No diagnostic manifestations (contractions, pain intensity, or specific dilation measurement) reliably demarcate its onset other than accelerating dilation 1
- Serial vaginal examinations at minimum 2-hour intervals are essential to detect when dilation rate increases 1, 2
- Uterine contraction assessment (palpation or Montevideo Units) has limited value for determining active phase onset, as contractions inconsistently increase and show no abrupt change distinguishing phase transitions 1
Normal Progression Rates
Normal dilation rates during active phase are ≥1.2 cm/hour for nulliparous women and ≥1.5 cm/hour for multiparous women. 1, 2
- These lower limits have been confirmed by diverse clinical investigators using objective instrumental methods 1
- Rates below these thresholds indicate protracted active phase requiring intervention 1
Management Algorithm
Monitoring Protocol
- Obtain serial cervical examinations every 2 hours minimum 1, 2
- Graph cervical dilation on a partogram to visualize progression rate 1, 2
- Continuous fetal monitoring is recommended 2
- Monitor oxygen saturation and provide adequate pain relief 2
Pain Management
- Epidural analgesia is preferred as it stabilizes cardiac output 2
- Nonpharmacologic methods should be offered 3
- Activity and ambulation should be encouraged when feasible 3
Management of Abnormal Progress
When active phase disorders are identified (dilation rate below normal thresholds), oxytocin augmentation should be administered for at least 4-6 hours before considering cesarean delivery for arrest. 2, 4
Specific Intervention Criteria:
- Do not diagnose labor arrest unless ≥6 cm cervical dilation has been reached OR labor has been stimulated for ≥6 hours 5
- Target uterine contraction pattern >200 Montevideo Units when using intrauterine pressure monitoring 4
- Minimum 4 hours of sustained adequate contractions (>200 Montevideo Units) before cesarean for arrest 4
- If adequate contraction pattern cannot be achieved, minimum 6 hours of oxytocin augmentation is required 4
Expected Outcomes with Adequate Augmentation:
- Nulliparous women: 56-74% vaginal delivery rate even after 4 hours without progress 4
- Parous women: 88-91% vaginal delivery rate even after 4 hours without progress 4
Abnormal Labor Patterns to Recognize
Several aberrant patterns can occur during active phase 1:
- Protracted dilation: Rate below normal thresholds (nulliparas <1.2 cm/h, multiparas <1.5 cm/h) 1
- Arrest of dilation: No cervical change despite adequate time and contractions 1
- Prolonged deceleration phase: Nulliparas >2-3 hours, multiparas >1 hour 1
- Failure of descent: Inadequate fetal descent during second stage 1
Risk Factors for Labor Abnormalities
Underlying factors that may contribute to active phase disorders include 1, 2:
- Cephalopelvic disproportion
- Excessive neuraxial block
- Poor uterine contractility
- Fetal malpositions or malpresentations
- Uterine infection
- Maternal obesity
- Advanced maternal age
- Previous cesarean delivery
Critical Decision Points
Cesarean delivery is justifiable when there is compelling clinical evidence of cephalopelvic disproportion, but only after adequate oxytocin augmentation (minimum 4-6 hours with adequate contractions or ≥6 cm dilation). 1, 4, 5
Important Caveats:
- A prolonged deceleration phase is strongly associated with disproportion and second stage abnormalities 1
- Shoulder dystocia risk increases if vaginal delivery occurs after prolonged deceleration 1
- Active management protocols (early amniotomy, 2-hourly assessments, early high-dose oxytocin) shorten first stage duration without affecting cesarean rates or maternal satisfaction 6
- Induced labors have longer active phase duration than spontaneous labors in nulliparous women (median 541 vs 433 minutes), which should be considered when assessing progress 7