Background: Delivery of the posterior arm, or the Barnum maneuver, is at times used late in shoulder dystocia management algorithms, and is not often a first- or second-line management protocol.
Case: A multiparous, diabetic patient, who was morbidly obese and had a residual obstetric brachial plexus injury, experienced a precipitous second stage of labor and severe shoulder dystocia. Attempts at the McRoberts maneuver with traction failed to deliver the fetus. In lieu of alternative maneuvers or continued attempts at traction, the posterior arm was delivered and the fetal trunk followed easily.
Conclusion: A geometric analysis reveals that using posterior arm delivery reduces the obstruction by more than a factor of two, relative to the McRoberts maneuver. We recommend earlier use of this maneuver during shoulder dystocia management.