How is synclitism managed during labor?

Management of Asynclitism During Labor

When asynclitism is detected during labor, the primary management strategy is to assess for cephalopelvic disproportion (CPD) and fetal malposition, as marked asynclitism occurs in 25-30% of cases with CPD and is strongly associated with occiput posterior/transverse positions, requiring either correction of the underlying malposition or proceeding to cesarean delivery if CPD cannot be excluded. 1, 2

Diagnostic Confirmation and Assessment

Clinical and Ultrasound Diagnosis

• Asynclitism should be confirmed using intrapartum ultrasound (transabdominal or transperineal approach) rather than relying solely on digital vaginal examination, as ultrasound provides objective, reproducible diagnosis with higher accuracy 3, 4, 5
• On transabdominal ultrasound, asynclitism appears as visualization of only one fetal orbit on the axial plane ("squint sign"), with the sagittal suture displaced anteriorly (posterior asynclitism) or posteriorly (anterior asynclitism) 4
• Moderate asynclitism (>15mm displacement) significantly increases the risk of birth trauma to the skull and brain, making accurate measurement critical 6

Mandatory Evaluation for Associated Conditions

• Assess fetal position immediately, as asynclitism is present in 53% of non-occiput anterior positions compared to only 6.7% of occiput anterior positions 2, 7
• Evaluate for CPD through serial examination looking for increasingly marked molding, deflexion, or asynclitism without descent—these are red flags indicating disproportion 1, 2
• Perform suprapubic palpation of the base of the fetal skull to differentiate true descent from molding alone 2
• Consider contributing factors: fetal macrosomia, maternal diabetes, obesity, pelvic adequacy, and excessive neuraxial blockade 1, 2

Management Algorithm

If CPD is Suspected or Cannot Be Excluded

• Proceed directly to cesarean delivery—oxytocin augmentation is contraindicated when CPD is present or suspected, as the risks of uterine rupture, fetal trauma, and maternal injury are too great 1, 2
• This is particularly critical because asynclitism with CPD leads to uneven distribution of tension forces on the tentorium cerebelli, causing one-sided ruptures and birth trauma 6

If CPD is Confidently Ruled Out

• Attempt correction of the underlying malposition (typically occiput posterior or transverse) as the primary intervention, since asynclitism is usually secondary to these positions 1, 3, 7
• Consider amniotomy combined with oxytocin augmentation for protracted active phase labor when asynclitism is present without CPD 2
• Start oxytocin at 1-2 mU/min, increasing by 1-2 mU/min every 15 minutes, targeting 7 contractions per 15 minutes (maximum 36 mU/min) 2

Monitoring During Management

• Perform serial cervical examinations every 2 hours after initiating intervention to assess progress 2
• Watch closely for emerging signs of CPD: increasingly marked molding, deflexion, or asynclitism without descent despite adequate contractions 1, 2
• If no progress occurs after 2 hours of adequate contractions, reassess for CPD and strongly consider cesarean delivery, as recent evidence suggests 2 hours is safer than the traditional 4-hour window after 6 cm dilation 2

Critical Pitfalls to Avoid

Operative Vaginal Delivery Considerations

• Asynclitism significantly increases the risk of difficult or failed instrumental delivery 3, 5
• If operative vaginal delivery is attempted, ultrasound guidance for correct application of vacuum or forceps is essential to prevent unnecessary cesarean delivery and reduce maternal/fetal morbidity 3
• Vacuum extraction and forceps application carry increased risks of birth trauma when asynclitism is present, including subaponeurotic hemorrhages and skull injuries 6

Timing of Intervention

• Do not delay decision-making—asynclitism is one of the most common causes of prolonged labor, dystocia, and obstructed labor 5
• The prevalence of operative delivery is higher in women with asynclitism (43% vs 27% without asynclitism), indicating the condition often does not resolve spontaneously 7
• Cesarean delivery in the second stage with asynclitism and impacted fetal head carries greater maternal morbidity (uterine extensions, hemorrhage, infection) and requires "pull" methods that risk fetal femoral and humeral fractures 8

Documentation Requirements

• Document the degree of asynclitism (mild vs moderate >15mm), associated fetal position, presence or absence of CPD indicators, and the rationale for management decisions 6
• Serial ultrasound measurements provide objective documentation of progression or worsening 4, 5