What is the definition of shoulder dystocia?

Definition of Shoulder Dystocia

Shoulder dystocia is defined as a vaginal birth where the obstetrician is unable to deliver the fetal shoulders with normal traction after delivery of the head, requiring additional maneuvers to complete delivery. 1

Key Diagnostic Criteria

Shoulder dystocia is diagnosed when one or both of the following occur:

• Need for additional maneuvers: When normal traction on the fetal head does not lead to delivery of the shoulders, requiring specific interventions beyond routine delivery techniques 1, 2

• Head-body delivery interval (HBDI) > 60 seconds: When the time between delivery of the fetal head and complete delivery of the body exceeds 60 seconds 3

Mechanism and Anatomical Considerations

Shoulder dystocia occurs when the anterior fetal shoulder becomes impacted behind the maternal pubic symphysis after delivery of the head. Less commonly, the posterior shoulder may become impacted on the maternal sacral promontory 3. This results in:

• Lack of space between the fetal head and maternal pubic symphysis
• Difficulty for the obstetrician to maneuver below the fetal head to disimpact it 1
• Potential obstruction of normal rotation and descent of the shoulders through the pelvis

Clinical Significance and Complications

Shoulder dystocia is a serious obstetric emergency with significant risks:

• Incidence: Complicates approximately 1.4% of all vaginal deliveries 1

• Maternal complications:

  • Increased risk of postpartum hemorrhage
  • Trauma to the bladder, anal sphincter, and rectum
  • Unintentional extension of the uterine incision during cesarean delivery 1, 2

• Fetal complications:

  • Brachial plexus injuries (18-21 fold increased risk with birth weight >4,500g) 1
  • Clavicular fractures (10-fold increased risk with birth weight >4,500g) 1
  • Hypoxia and potential neurological damage 2

Risk Factors

While shoulder dystocia often occurs unpredictably, several risk factors have been identified:

• Fetal macrosomia: Risk increases significantly with estimated fetal weight >4,500g 1
• Maternal diabetes: Risk of shoulder dystocia is 19.9-50% in diabetic pregnancies with fetal weight >4,500g 1
• Previous shoulder dystocia: History increases risk in subsequent deliveries 2
• Prolonged second stage of labor: Particularly with prolonged deceleration phase 1
• Operative vaginal delivery: Instrumented deliveries increase risk 4

Management Approach

When shoulder dystocia occurs, a systematic approach is essential:

1. Recognition and announcement: Clearly announce "shoulder dystocia" to mobilize team assistance 2

2. First-line maneuvers:

   • McRoberts maneuver: Maternal legs hyperflexed tightly to abdomen 1
   • Suprapubic pressure: Applied to displace the anterior shoulder 1, 2

3. Second-line maneuvers (if first-line fails):

   • Posterior arm delivery: Extracting the posterior arm and shoulder
   • Internal rotational maneuvers: To change the position of the shoulders 2

4. Additional interventions (rarely needed):

   • Intentional clavicular fracture
   • Cephalic replacement (Zavanelli maneuver) 2

Prevention and Training

Simulation-based training is crucial for improving outcomes:

• Regular team-based simulation exercises improve performance during actual events 2
• Training should include all potential maneuvers and clear communication protocols 1
• Timing of interventions should be practiced, with emphasis on tracking the head-body delivery interval 3

Important Caveats

• Despite known risk factors, most cases of shoulder dystocia occur without warning 2
• Prophylactic cesarean delivery based solely on suspected macrosomia is not supported by evidence 1
• Attempting delivery during a uterine contraction can worsen the impaction of the fetal shoulders 1

Shoulder dystocia remains one of the most challenging and unpredictable obstetric emergencies, requiring immediate recognition and systematic management to minimize maternal and fetal complications.