New FIGO Diagnoses for Dysfunctional Labor: Early Active Phase and True Active Phase
Active Phase Onset and Definition
The active phase of labor is now defined by an accelerating cervical dilation rate detected through serial examinations (minimum every 2 hours), rather than a fixed centimeter threshold, though the steepest acceleration typically occurs between 5-6 cm of dilation. 1
Active labor onset is identified solely by observing when the cervical dilation rate accelerates from the flat slope of the latent phase to more rapid progression—no specific dilation measurement (e.g., 4 cm or 6 cm) is required for diagnosis. 1
Serial vaginal examinations performed at least every 2 hours are essential to recognize this transition, as no clinical signs (contraction strength, pain intensity, or specific dilation measurement) reliably demarcate active labor onset. 1
The acceleration phase—where the steepest increase in cervical dilation occurs—is typically observed between 5 cm and 6 cm of dilation. 1
Normal Cervical Dilation Rate Thresholds
In the true active phase, normal dilation rates are ≥1.2 cm/hour for nulliparous patients and ≥1.5 cm/hour for multiparous patients. 1
These lower-limit thresholds (1.2 cm/h for nulliparas, 1.5 cm/h for multiparas) have been validated by multiple investigators using objective instrumental methods such as intra-uterine pressure catheters. 1
Dilation rates falling below these thresholds signify a protracted active phase and warrant clinical intervention. 1
The widely cited 0.6 cm/hour threshold represents an absolute minimum rate, but rates this slow likely indicate patients still in latent phase rather than true active labor. 2, 3
Diagnosis of Protracted Active Phase
Protracted active phase is diagnosed when cervical dilation is slower than 1.2 cm/hour in nulliparous patients or 1.5 cm/hour in multiparous patients during confirmed active labor. 1, 3
The diagnosis cannot be made unless the patient has already entered the active phase—this is a critical pitfall to avoid, as mislabeling latent-phase patients leads to unnecessary interventions. 1
A minimum acceptable dilation rate of 0.6 cm/hour has been proposed, but this threshold likely includes many patients still in latent phase. 3
Arrest of Dilation Criteria
Arrest of dilation is defined as absence of cervical change despite adequate observation and sufficient uterine contractions, with timing thresholds that vary by degree of cervical dilation. 1
Graduated Arrest Criteria by Cervical Dilation:
At 4-5 cm dilation: A 4-hour observation window with adequate contractions remains appropriate before diagnosing arrest. 3
At 6 cm or greater: Recent evidence suggests that a 4-hour arrest window may be excessive, with a 2-hour window being safer to prevent adverse maternal and neonatal outcomes. 3, 4
At 8-9 cm dilation: Allowing arrest ≥4 hours is associated with increased risks of cesarean delivery (adjusted OR 0.40 for <4 hours vs 4-5.9 hours), chorioamnionitis (adjusted OR 0.42), and adverse neonatal composite outcomes (adjusted OR 0.51). 4
Deceleration Phase Recognition
The deceleration phase occurs near complete dilation when cervical change slows as the fetus descends, marked by increased and painful contractions. 1
A prolonged deceleration phase (>2-3 hours in nulliparous patients, >1 hour in multiparous patients) is strongly associated with cephalopelvic disproportion and second-stage abnormalities, including increased risk of shoulder dystocia. 1
Critical Clinical Pitfalls
Do not rely on uterine contraction assessment alone (palpation or Montevideo Units) to determine labor phase, as contraction patterns rise inconsistently and lack an abrupt change at phase transition. 1
Avoid diagnosing protracted active phase in patients still in latent labor—this requires confirming active phase entry through serial examinations showing accelerating dilation. 1
Do not apply a uniform 4-hour arrest criterion across all cervical dilations—use graduated thresholds with shorter windows (2 hours) after 6 cm to optimize maternal-fetal safety. 3, 4