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Shoulder dystocia: Intrapartum diagnosis, management, and outcome

Author
John F Rodis, MD
Section Editor
Charles J Lockwood, MD, MHCM
Deputy Editor
Vanessa A Barss, MD, FACOG

INTRODUCTION

A vaginal delivery is complicated by shoulder dystocia when, after delivery of the fetal head, additional obstetric maneuvers beyond gentle traction are needed to enable delivery of the fetal shoulders. It represents an obstetric emergency. Few shoulder dystocias can be anticipated and prevented, as most occur in the absence of risk factors. Therefore, the obstetrician must be prepared to recognize a shoulder dystocia immediately and proceed through an orderly sequence of steps to affect delivery in a timely manner. The goal of management is to prevent fetal asphyxia and permanent Erb's palsy or death, while avoiding physical injury (eg, bone fractures, maternal trauma), but the latter are acceptable if needed to prevent permanent injury in the child.

Intrapartum diagnosis and management of shoulder dystocia will be reviewed here. Risk factors for shoulder dystocia and planning delivery of pregnancies at high risk are discussed separately. (See "Shoulder dystocia: Risk factors and planning delivery of high-risk pregnancies".)

PATHOPHYSIOLOGY

The fetal bisacromial diameter (the distance between the outermost parts of the fetal shoulders) normally enters the pelvis at an oblique angle with the posterior shoulder ahead of the anterior one, rotating to the anterior-posterior position at the pelvic outlet with external rotation of the fetal head. The anterior shoulder can then slide under the symphysis pubis for delivery (figure 1). If the fetal shoulders remain in an anterior-posterior position during descent or descend simultaneously rather than sequentially into the pelvic inlet, then the anterior shoulder can become impacted behind the symphysis pubis; the posterior shoulder may be obstructed by the sacral promontory. Anterior obstruction is more common than posterior obstruction. If descent of the fetal head continues while the anterior or posterior shoulder remains impacted, then stretching of the nerves in the brachial plexus may occur and may result in nerve injury.

It is hypothesized that the fetal trunk fails to rotate to an oblique position because of increased resistance between the fetal skin and vaginal walls or a large fetal chest relative to the biparietal diameter, which may occur with macrosomia, or because of rapid fetal descent, which may occur with precipitous labor [1,2].

Neonatal injuries diagnosed at birth may be caused by prenatal, as well as intrapartum, events. Labor and the impacted shoulder itself or the provider's attempt to deliver the infant may result in traumatic injury. Umbilical cord compression, compression of fetal neck vessels leading to cerebral venous obstruction, excessive vagal stimulation and bradycardia, or a combination of factors may result in asphyxia [3,4].

                                  
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Literature review current through: Sep 2017. | This topic last updated: Jun 22, 2017.
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