In cases of shoulder dystocia, the upper fetal shoulder is impacted on the pubic symphysis, or more rarely, the lower shoulder becomes impacted on the sacral promontory or nonexible coccyx. In either case, this event prevents delivery of the baby. Shoulder dystocia can be a potentially catastrophic event since the fetal thorax is still within the pelvis and cannot properly expand for breathing.
While the rate of shoulder dystocia is higher with gestational diabetic women and macrosomic fetuses (>4500 grams at birth), most cases of shoulder dystocia occur with average-sized fetuses.
If a brachial plexus palsy (brachioplexopathy) occurs, it usually affects the portions of the brachial plexus that control the shoulder and elbow. Spontaneous recovery is the rule rather than the exception.
Most fetuses are successfully delivered with a combination of McRoberts maneuver and suprapubic pressure.