How is shoulder dystocia diagnosed?

Diagnosis of Shoulder Dystocia

Shoulder dystocia is definitively diagnosed when additional obstetric maneuvers are required to deliver the fetal shoulders after the head has delivered and gentle traction has failed. 1

Definition and Incidence

• Shoulder dystocia occurs when normal traction on the fetal head does not lead to delivery of the shoulders, creating an obstetric emergency that requires additional maneuvers 2
• It complicates approximately 0.5-1% of vaginal deliveries 1
• Despite its relatively low incidence, shoulder dystocia represents a significant obstetric emergency due to potential maternal and neonatal complications 3

Diagnostic Criteria

• The diagnosis is made when:
  • The fetal head has delivered
  • Gentle traction has failed to deliver the shoulders
  • Additional obstetric maneuvers become necessary 1, 3
• This is a clinical diagnosis made during the delivery process, not a prenatal diagnosis 2
• The "turtle sign" may be observed, where the delivered head retracts against the perineum (appears to be pulled back into the vagina) 2

Risk Factors

While shoulder dystocia often occurs without warning, several risk factors have been identified:

• Previous shoulder dystocia (strongest predictor) 1
• Fetal macrosomia (especially with estimated fetal weight >4500g) 1
• Maternal diabetes (preexisting or gestational) 1
• Maternal obesity 1
• Prolonged second stage of labor 4
• Prolonged deceleration phase of labor 4
• Operative vaginal delivery 2

It's important to note that 50-70% of shoulder dystocia cases occur in the absence of identifiable risk factors, making it largely unpredictable 1, 5

Warning Signs During Labor

• A prolonged deceleration phase (from 8-10 cm dilation) may signal potential shoulder dystocia 4
• When the deceleration phase is prolonged and associated with disorders of fetal descent, there is a higher risk of shoulder dystocia if vaginal delivery occurs 4
• Arrest of descent in the second stage of labor, especially with suspected fetal macrosomia, should raise concern 6

Differential Diagnosis

When encountering difficulty delivering the shoulders after the head has emerged, the diagnosis is typically straightforward. However, clinicians should consider:

• Normal physiologic delay in shoulder delivery (distinguished by successful delivery with gentle traction)
• Tight nuchal cord preventing shoulder delivery (requires identification and management of the cord)
• Fetal anomalies affecting shoulder delivery 2

Prevention Considerations

While shoulder dystocia cannot be reliably predicted, certain preventive measures may be considered:

• Induction of labor at 39 weeks or beyond when macrosomia is suspected and the cervix is favorable 1
• Consideration of cesarean delivery in specific high-risk situations:
  • Estimated fetal weight >4500g with maternal diabetes 1
  • Estimated fetal weight >5000g without diabetes 1
  • History of shoulder dystocia with severe complications 1
  • During labor when macrosomia is present with failure to progress in second stage and fetal head station above +2 1

Management Preparation

• Simulation training for all delivery room personnel is strongly recommended as it reduces neonatal injury 1, 5
• Healthcare providers should be familiar with at least two maneuvers beyond the McRoberts maneuver 1
• Clear communication and team coordination are essential when shoulder dystocia is identified 2

Remember that shoulder dystocia remains largely unpredictable despite known risk factors, making preparedness and proper management crucial for reducing associated complications.