Chapter 222 Shoulder Dystocia
Description: Shoulder dystocia is an obstruction to delivery caused by impaction of the fetal shoulder behind the maternal symphysis. Less commonly it can be due to impaction of the posterior fetal shoulder on the sacral promontory. Shoulder dystocia is most often an unpredictable and unpreventable obstetric emergency, usually defined as a delivery that requires additional obstetric maneuvers (following failure of gentle downward traction on the fetal head) to effect delivery of the shoulders.
Prevalence: 0.15% of fetuses weighing ≥2500 g (5 pounds 8 oz), 1% to 5% for ≥4000 g (8 pounds 13 oz), 19% ≥4500 g (9 pounds 15 oz); overall 0.6% to 1.4% of vertex deliveries.
Causes: A relative disproportion between fetus and the birth passage or a misalignment of normally sized structures (fetus and pelvis).