Arrest of Descent During Labor
Arrest of descent is defined as the cessation of fetal descent during the second stage of labor, specifically when there is no change in fetal station despite adequate uterine contractions and maternal expulsive efforts. 1
Clinical Definition and Timing
Arrest of descent occurs during the second stage of labor (from complete cervical dilation to delivery) and represents one of three distinct graphic abnormalities of descent, alongside protracted descent and failure of descent. 1
Key Diagnostic Criteria
- No progression of fetal station measured by serial vaginal examinations over time 1
- Must occur in the context of adequate uterine contractions 2
- Requires differentiation between true descent versus molding through serial suprapubic palpation of the base of the fetal skull 3
Clinical Significance and Associated Risks
Strong Association with Cephalopelvic Disproportion (CPD)
Arrest of descent has a strong association with CPD, occurring in approximately 52% of cases in nulliparous women. 4 This makes thorough cephalopelvimetric assessment imperative before considering any intervention. 3
Risk Factors
The following factors significantly increase the risk of arrest of descent:
- Nulliparity (OR=7.8, most significant risk factor) 5
- Fetal macrosomia (birth weight >4 kg; OR=2.3) 5
- Epidural analgesia (OR=1.8) 5
- Hydramnios (OR=1.6) 5
- Hypertensive disorders (OR=1.5) 5
- Gestational diabetes (OR=1.5) 5
- Male fetal gender (OR=1.4) 5
- Fetal malpositions (occiput posterior and transverse) 3, 1
- Maternal obesity 1
- Excessive neuraxial block 1
Relationship to Deceleration Phase Abnormalities
A prolonged deceleration phase is frequently accompanied by failure of descent and serves as a harbinger of second stage labor abnormalities. 3 The combination of a prolonged deceleration phase with any disorder of fetal descent makes safe vaginal delivery very unlikely. 3
Prognostic Indicators
Adverse Prognostic Factors
- High fetal station at time of arrest correlates with poor delivery outcome 4
- Long duration of arrest adversely affects delivery outcomes 4
- Arrest occurring during oxytocin administration is particularly ominous—no patients in one study delivered vaginally when arrest occurred during oxytocin infusion 4
Favorable Prognostic Indicators
Post-arrest progression at a rate equal to or greater than pre-arrest descent is a favorable sign for delivery outcome. 4 This suggests that if descent resumes after intervention, the rate of resumed descent provides important prognostic information. 4
Perinatal Outcomes
Deliveries complicated by arrest of descent result in:
- Cesarean section in 20.6% of cases 5
- Vacuum extraction in 74.0% of cases 5
- Forceps delivery in 5.4% of cases 5
Newborns delivered after arrest of descent have significantly higher rates of low Apgar scores (<7 at 1 minute: 12.7% vs. 2.1%; at 5 minutes: 0.9% vs. 0.2%). 5 However, perinatal mortality rates are not significantly different from controls. 5
Risk of Shoulder Dystocia
If vaginal delivery occurs after arrest of descent, there is increased risk of shoulder dystocia and brachial plexus injury, particularly when associated with a prolonged deceleration phase. 3, 6
Common Pitfalls
- Confusing molding with true descent: Always use serial suprapubic palpation of the fetal skull base to confirm actual descent rather than relying solely on vaginal examination, which may be misleading due to caput formation or molding. 3
- Failing to assess for CPD before intervention: Given the 52% association with CPD, thorough cephalopelvimetric assessment is mandatory before attempting oxytocin augmentation or operative vaginal delivery. 4, 3
- Using oxytocin when arrest occurs during existing oxytocin administration: This scenario has particularly poor prognosis for vaginal delivery. 4