From the Guidelines
Predisposing factors for shoulder dystocia include fetal macrosomia, maternal diabetes, and post-term pregnancy, among others, as identified in the most recent and highest quality study 1. The most significant risk factors for shoulder dystocia are:
- Fetal macrosomia, which is often associated with maternal diabetes and can lead to a size mismatch between the fetal shoulders and the maternal pelvis 1
- Maternal diabetes, which increases the risk of shoulder dystocia due to disproportionate growth of the fetal trunk and shoulders compared to the head 1
- Post-term pregnancy, which can increase the risk of shoulder dystocia due to the larger size of the fetus 1
- Previous shoulder dystocia, which increases the risk of recurrence in subsequent pregnancies 1
- Instrumental delivery, particularly vacuum extraction, which can increase the risk of shoulder dystocia due to the increased force applied to the fetal head and shoulders 1 It's essential to note that shoulder dystocia can occur unpredictably, with approximately 50% of cases having no identifiable risk factors 1. Therefore, healthcare providers should be prepared for potential shoulder dystocia in all deliveries, but especially vigilant when these risk factors are present.
The underlying mechanism of shoulder dystocia involves a size mismatch between the fetal shoulders and the maternal pelvis, where the anterior fetal shoulder becomes impacted against the maternal pubic symphysis after delivery of the head 1. This can lead to serious complications, including clavicular fracture and brachial plexus palsy, which can have long-term consequences for the infant's health and quality of life 1.
In terms of prevention and management, the U.S. Preventive Services Task Force recommends screening for gestational diabetes mellitus (GDM) after 24 weeks of gestation to reduce the risk of preeclampsia, macrosomia, and shoulder dystocia 1. Early detection and treatment of GDM can help prevent these complications and improve maternal and fetal outcomes.
Overall, the key to preventing and managing shoulder dystocia is to be aware of the risk factors and to take a proactive approach to preventing and managing them. This includes screening for GDM, monitoring fetal growth and development, and being prepared for potential complications during delivery. By taking these steps, healthcare providers can help reduce the risk of shoulder dystocia and improve outcomes for mothers and infants.
From the Research
Predisposing Factors for Shoulder Dystocia
The predisposing factors for shoulder dystocia include:
- Fetal macrosomia, which is a significant risk factor for shoulder dystocia 2, 3, 4, 5, 6
- Maternal diabetes, which increases the risk of shoulder dystocia, even at lower birth weight thresholds than at which cesarean delivery is currently offered 3, 4, 5
- Previous history of shoulder dystocia, which is a risk factor for recurrent shoulder dystocia 2
- Maternal obesity, which is a risk factor for shoulder dystocia 5, 6
- Prolonged second stage of labor with midpelvic delivery, which increases the risk of shoulder dystocia 6
- Estimated fetal weight (EFW) greater than 4500 g if associated with maternal diabetes, and greater than 5000 g in the absence of maternal diabetes, which are indications for cesarean delivery to prevent shoulder dystocia 2
Risk Factors Associated with Diabetes
In diabetic pregnancies, the risk factors for shoulder dystocia include: