Labor may sometimes arrest due to shoulder dystocia. Shoulder dystocia cannot be predicted or prevented, be-cause accurate methods for identifying which fetuses will experience this complication do not exist. Antepartum conditions associated with shoulder dystocia include multi-parity, postterm gestation, previous history of a macro-somic birth, and a previous history of shoulder dystocia. Although fetal macrosomia increases the risk of shoulder dystocia, elective induction of labor or elective cesarean de-livery for all women suspected of carrying a fetus with macrosomia is not appropriate.
Diagnosis of shoulder dystocia has a subjective compo-nent, especially in less severe forms. The delivered fetal head may retract against the maternal perineum (turtle sign) and, if so, may assist in the diagnosis. Interventions that may be used to facilitate delivery include the McRoberts maneu-ver and the application of suprapubic pressure to assist in dislodging the impacted shoulder (Fig. 9.9). In contrast, fundal pressure may further worsen impaction of the shoul-der and also may result in uterine rupture. Controversy ex-ists as to whether episiotomy is necessary, because shoulder dystocia typically is not caused by obstructing soft tissue. Direct fetal manipulation with either rotational maneuvers or delivery of the posterior arm also may be used. In severe cases, more aggressive interventions, such as the Zavanelli maneuver (in which the fetal head is flexed and reinserted into the vagina to reestablish umbilical cord blood flow and delivery performed through fracture of the fetal clavicle, may be performed. Regardless of the procedures used, brachial plexus injury is associated with shoulder dystocia; incidence ranges from 4% to 40%. However, most cases resolve without permanent disability; fewer than 10% of all cases of shoulder dystocia result in a persistent brachial plexus injury.