In a term pregnancy with a fully dilated cervix and a prolonged arrest of fetal descent during the deceleration phase of the second stage of labor, what is the safest initial management?

Management of Prolonged Deceleration Phase with Arrest of Descent

When a prolonged deceleration phase is accompanied by arrest of fetal descent at full cervical dilation, you should suspect cephalopelvic disproportion (CPD) and prepare for cesarean delivery rather than prolonged attempts at vaginal delivery. 1, 2

Clinical Significance and Warning Signs

The deceleration phase represents the terminal phase of cervical dilation where the cervix "turns the corner" as it retracts cephalad around the fetal head. 1 This phase is critically important because:

• Cervical dilation and fetal descent are interdependent processes - complete dilation generally will not occur unless fetal descent also takes place, and vice versa. 1, 2
• A prolonged deceleration phase with delayed fetal descent is a red flag for CPD and should prompt immediate suspicion of fetopelvic disproportion. 1, 2
• This pattern predicts second stage abnormalities and increased shoulder dystocia risk if vaginal delivery is attempted. 1, 2

Initial Assessment Algorithm

When encountering this scenario, systematically evaluate:

1. Fetal factors: Assess for macrosomia (birth weight >4000g is a well-documented cause of arrest of descent), fetal position, attitude, and degree of cranial molding. 3, 4
2. Pelvic architecture: Evaluate pelvic capacity to accommodate the fetus and likelihood of CPD. 3, 5
3. Uterine contractility: Assess adequacy of contractions. 3
4. Fetal station: Document current station and any progression or lack thereof. 3, 5
5. Risk factors: Look for gestational diabetes, prior macrosomic infant, maternal obesity, uterine infection, or excessive sedation. 3, 4

Management Decision Points

If thorough fetopelvic assessment reveals high probability of CPD, proceed directly to cesarean delivery. 1, 2 This is particularly critical because:

• CPD is associated with arrest of descent in 52% of cases. 5
• Cesarean delivery in the second stage carries greater maternal morbidity than operative vaginal delivery, but attempting vaginal delivery with unrecognized CPD leads to worse outcomes. 6

Oxytocin should NOT be used if CPD is suspected. 3, 5 Historical data shows that arrest of descent occurring during oxytocin administration is particularly ominous - no patients in one series subsequently delivered vaginally. 5 Additionally, oxytocin stimulation followed by operative delivery had adverse fetal effects. 5

When Conservative Management May Be Considered

Oxytocin may only be considered if:

• Thorough assessment reveals LOW probability of CPD 3
• An identifiable inhibitory factor is present (dense neuraxial block, excessive sedation) 3, 5
• The plan is to allow the inhibitory agent to abate expectantly rather than augment labor 5

The best delivery prognosis occurs when causative inhibitory agents (peridural anesthesia, sedation) are allowed to abate expectantly. 5

Critical Pitfalls to Avoid

• Do not continue expectant management indefinitely - neither immediate operative delivery nor prolonged expectancy (except for specific abatement of inhibitory factors) is appropriate. 5
• Do not use oxytocin empirically - it should only be used after thorough fetopelvic assessment rules out CPD. 3, 5
• Monitor fetal heart rate patterns closely - prolonged end-stage FHR decelerations in second stage can be associated with poor outcomes and require rapid delivery. 7
• Avoid midforceps procedures with rotation when CPD is present - these are associated with neonatal depression and birth trauma. 5

Prognostic Indicators

Favorable signs if attempting vaginal delivery:

• Post-arrest progression at a rate equal to or greater than pre-arrest descent 5
• Low fetal station at time of arrest 5
• Short duration of arrest 5

Unfavorable signs mandating cesarean:

• High fetal station at arrest 5
• Long duration of arrest 5
• Arrest during oxytocin administration 5
• Evidence of macrosomia, especially in multiparas with prior macrosomic infants and gestational diabetes 4