Understanding Shoulder Dystocia: Key Risk Factors and Prevention Strategies

Shoulder dystocia is a rare but serious obstetric emergency that occurs in about 0.2–3% of vaginal deliveries. It happens when the baby’s anterior shoulder becomes stuck behind the maternal pubic symphysis after the head is delivered. While it often occurs unexpectedly, several maternal, fetal, and intrapartum factors can increase the risk. Recognizing shoulder dystocia risk factors early allows care teams to plan for safer deliveries and reduce complications.

Key Shoulder Dystocia Risk Factors

1. Fetal Macrosomia
   • Estimaged fetal weight ≥ 4,000–4,500 g significantly raises the risk.
   • In diabetic pregnancies over 4,500 g, the risk can reach 10–20% (Chauhan et al., 2005; ACOG PB No. 178, 2017).
2. Maternal Diabetes
   • Gestational and pregestational diabetes increase fetal shoulder mass, doubling to quadrupling dystocia risk (Boulet et al., 2003; Weiss et al., 2004).
3. Prior Shoulder Dystocia
   • Recurrence risk ranges from 10–25%, especially with higher fetal weight in later pregnancies (Stotland et al., 2004; ACOG, 2017).
4. Maternal Obesity and Excessive Weight Gain
   • Both are linked to macrosomia and longer labor durations (Crane et al., 2009).
5. Operative Vaginal Delivery (OVD)
   • Use of vacuum or forceps increases risk, especially when combined with macrosomia or midpelvic delivery (Leung & Lao, 2002).
6. Short Maternal Stature
   • Maternal height has been identified as an independent risk factor in recurrent cases (Tingleff et al., 2022).
7. Prolonged Second Stage of Labor
   • A longer second stage often indicates mechanical difficulty and correlates with dystocia, particularly in large infants or operative vaginal delivery (OVD) cases (Gherman et al., 2006).

Clinical Insights on Shoulder Dystocia

• Most shoulder dystocia cases occur without identifiable risk factors (ACOG, 2017).
• Risk factors are additive, meaning the combination of conditions (for example, macrosomia plus maternal diabetes and OVD) raises the odds significantly.
• Emerging machine learning models now identify birthweight, maternal BMI, and cervical dilation timing as top predictors (AJOG, 2023).

Practice Recommendations for Safer Deliveries

• Counsel high-risk patients early about delivery options, particularly when estimated fetal weight exceeds 4,500 g in diabetic pregnancies.
• Conduct interdisciplinary drills and simulations to ensure every team member understands shoulder dystocia management protocols.
• Document any prior dystocia events, discuss recurrence risk with patients, and maintain clear communication during labor.
• Carefully consider the use of vacuum or forceps in high-risk deliveries.

Why Preparation Matters

Even though shoulder dystocia cannot always be predicted, preparation makes all the difference. A coordinated, well-trained response can prevent serious complications and improve maternal and neonatal outcomes. Comprehensive emergency preparedness improves outcomes.

References

1. ACOG Practice Bulletin No. 178. (2017). Shoulder Dystocia. Obstet Gynecol, 129(5), e123–e133.
2. Boulet SL et al. (2003). Macrosomic births in the U.S. Am J Obstet Gynecol, 188(5), 1372–8.
3. Chauhan SP et al. (2005). Macrosomia review. Am J Obstet Gynecol, 193(2), 332–46.
4. Tingleff J et al. (2022). Recurrence of shoulder dystocia. Acta Obstet Gynecol Scand, 101(12), 1321–1329.
5. Zork N et al. (2023). Risk modeling for shoulder dystocia using ML. Am J Obstet Gynecol. DOI: 10.1016/j.ajog.2022.11.135
6. Crane JMG et al. (2009). Gestational weight gain and outcomes. J Obstet Gynaecol Can, 31(1), 28–35.

Maternal 911 Education Systems, LLC is a leader in emergency obstetrics and team training, improving outcomes through education and evidence-based practice.

Maternal 911 Education Systems, LLC is led by a team of experts in emergency obstetrics and maternal safety, dedicated to improving outcomes through evidence-based, team-centered education. Passionate about maternal health education, Maternal 911 advocates for evidence-based practices and interdisciplinary team training. Their mission is to reduce pregnancy risks through education and emergency training. Learn more at maternal911.com.

Click here to contact us with any questions.

Educational use only — not a substitute for clinical judgment or local protocols.