Shoulder Dystocia

Samreen Vora

OVERVIEW

Shoulder dystocia is an unpredictable complication of vaginal delivery and is defined as failure to deliver the fetal shoulders with gentle downward traction, thereby requiring additional maneuvers to affect delivery.¹ Shoulder dystocia is an obstetric emergency as it can result in maternal morbidity as well as infant morbidity and mortality. The incidence varies from 0.2% to 3%, with 1 in every 22,000 term vaginal deliveries resulting in a neonate with hypoxic ischemic encephalopathy secondary to shoulder dystocia.²^,³^,⁴ The likelihood of encountering a shoulder dystocia during a precipitous delivery in the emergency department is low but the potential impact on two patients is substantial; therefore, the need for health care providers to be prepared for this emergency is paramount.

Risk Factors

Shoulder dystocia occurs unpredictably and is unpreventable but there are a number of known risk factors. The primary identified risk factor is a neonatal birth weight greater than 4000 g. Estimating birth weight is notoriously challenging, adding to the difficulty in predicting a shoulder dystocia.⁵^,⁶ Most cases of shoulder dystocia occur in women with normal-sized infants, whereas delivery of most large birth weight infants does not result in shoulder dystocia.⁷^,⁸ Shoulder dystocia in a previous delivery is an independent risk factor for recurrence.⁹^,¹⁰ Risk factors that are implicated include maternal diabetes, obesity, older age at first birth, multiparity, operative vaginal delivery, prolonged second stage of labor, and fetal macrosomia. There are no definitive data to support these as independent risk factors, and a combination of multiple risk factors may play a role.⁵^,¹¹^,¹²^,¹³ There are no identified risk factors for up to 50% of vaginal deliveries that encounter a shoulder dystocia.¹¹

CLINICAL FEATURES

Shoulder dystocia is an obstetric emergency, and although it cannot be predicted or prevented, the clinical recognition and diagnosis is essential in order to initiate timely management to prevent fetal and/or maternal morbidity and mortality. Studies indicate that there is increased risk of fetal asphyxia in a term infant after 5 minutes of an impacted shoulder.¹⁴^,¹⁵ The literature demonstrates inconsistent identification and diagnosis of shoulder dystocia with wide-ranging incidence.¹^,²^,³ This variability may be secondary to a variety of factors, including inconsistent definitions of shoulder dystocia and subjectivity of provider assessment and identification.¹

A shoulder dystocia is diagnosed when the descent of the fetal anterior shoulder is obstructed by the maternal pubic symphysis, or less commonly the fetal posterior shoulder is impacted on the maternal sacral promontory. There may be a notable retraction of the delivered fetal head against the maternal perineum called the “turtle sign.” This subtle sign can be an indication of shoulder dystocia.¹ The diagnosis is clear when gentle traction is not sufficient to deliver the fetus.

MANAGEMENT

Once a shoulder dystocia is identified, an immediate call for help must be made. The goal of treatment is to perform maneuvers that increase the functional diameter of the pelvic ring, decrease the breadth of the fetal shoulders, or change the relationship of the breadth of the fetal shoulders within the pelvis. As soon as a shoulder dystocia is identified, the pregnant woman should be instructed to stop pushing and a shoulder dystocia announced in order to create a shared mental model among the team. Simultaneous with initiating maneuvers to resolve the impaction, a call for assistance should occur to include nursing, obstetrics, anesthesia, and neonatology/pediatrics.

A systematic approach to resolve a shoulder dystocia should be followed if possible (Figure 26.1), but the management may vary based on the clinical situation and the provider
comfort with particular maneuvers. There are no randomized controlled trials indicating the superiority of one maneuver over another; therefore, variation in approach is reasonable. Computer models indicate that delivery of the posterior arm exerts less force on the fetus. As time is of the essence in this obstetric emergency, each maneuver is attempted only a few times before quickly moving to the next. The literature indicates that regardless of maneuver, there is still risk of maternal and neonatal complications, and the more maneuvers required to deliver the infant, the higher the risk of fetal injury.¹ The provider should avoid any forceful downward traction during delivery and the need for increased traction is an indication to utilize additional maneuvers to release a likely shoulder dystocia.

Figure 26.1: Shoulder dystocia treatment algorithm.

McRoberts Maneuver and Suprapubic Pressure

The first maneuver to attempt when a shoulder dystocia is suspected is the McRoberts maneuver. This maneuver is recommended as it is simple, the least invasive, and shown to be up to 42% effective.⁴ For this maneuver, two assistants on each side of the patient grasp the maternal legs and flex them against the abdomen. This allows for rotation of the pubic symphysis and flattening of the maternal lumbar lordosis, ultimately dislodging the impacted shoulder. At the same time, an assistant can use a palm or fist to apply downward pressure above the maternal pubic bone (Figure 26.2). Fundal pressure should be avoided in order to prevent uterine rupture and further fetal impaction.¹

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