Shoulder dystocia is defined as the impaction of the anterior shoulder against the pubic symphysis after the delivery of the head and occurs when the breadth of the shoulder is greater than the biparietal diameter of the head (Fig. 21-8). It is a life-threatening event associated with significant morbidity and mortality that needs to be recognized early and managed promptly. The overall incidence of shoulder dystocia is 0.3% to 1% but increases to 5% to 7% for newborns with macrosomia (birth weight >4500 g). Although a number of factors are associated with its occurrence, their predictive values are low, making it incumbent on the practitioner to be ever vigilant.
Several maternal and fetal complications are associated with shoulder dystocia (Carlan, 1991). Maternal complications are usually a consequence of soft tissue damage. The attempt to deliver the baby can result in an extension of an episiotomy to a fourth-degree laceration, with disruption of the anal sphincter and rectal mucosa. Other complications include hemorrhage secondary to uterine atony, vaginal lacerations, and rarely uterine rupture.
Fetal complications tend to be more profound. Brachial plexus injury can occur. Most resolve within 6 months with adequate physical therapy. However, the injury may persist as a source of lingering disability. Erb's palsy is the most common brachial plexus injury and involves the fifth and sixth cervical roots. Klumpke's palsy involves injury to the
eighth cervical root and the first thoracic fibers. Clavicular fracture may occur spontaneously or intentionally and may rarely result in damage to the underlying tissue. Prolonged fetal hypoxia secondary to a delay in the delivery can result in severe neurologic damage and even death.
Conditions that predispose to development of shoulder dystocia are related to either a macrosomic fetus or a contracted pelvis. Importantly, however, approximately one half of all shoulder dystocias occur with normal-weight fetuses and are unanticipated. Predisposing conditions include prepregnancy weight of greater than 180 pounds, excessive maternal weight gain, a history of diabetes or abnormal glucose tolerance, advanced maternal age, or a post-term pregnancy.
The key to management of this condition is anticipation and preparation. Warning signs include a prolonged second stage of labor or use of a vacuum or forceps. Once a shoulder dystocia becomes apparent, a number of maneuvers can be used to disimpact the shoulder (Fig. 21-9). The McRoberts maneuver is a time-honored and proven technique that is ideal in initial management (Gherman et al., 1997). It involves the flexion of the maternal thighs onto the abdomen, which increases the inlet diameter, straightens the lumbosacral lordosis, and removes the sacral prominence as a possible obstruction to delivery. This procedure is often done with suprapubic pressure to dislodge the offending shoulder from behind the maternal pubic symphysis. In contrast to suprapubic pressure, fundal pressure, which often serves to exacerbate the condition, should not be exerted. Other measures include the Woods' screw maneuver, an attempt to apply pressure to the back of the posterior shoulder to rotate the fetus, free the anterior shoulder, and attempt delivery obliquely. Alternately, delivery of the posterior arm can be attempted. Finally, as a measure of last resort, the Zavanelli maneuver, the cephalic replacement of the fetus followed by cesarean delivery, can be attempted.
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