Step 1: Approach this as a protocol-ordering question. Shoulder dystocia is handled by the HELPERR algorithm, and the answer is whichever step immediately follows McRoberts.
Step 2: Recall the order: call for Help, consider Episiotomy, perform the Legs/McRoberts hip hyperflexion, then external suprapubic Pressure, then internal Enter rotations, then Remove the posterior arm, then Roll to all fours.
Step 3: Since McRoberts (the legs step) has been completed, the next escalation is suprapubic pressure - pushing just above the pubic bone to rotate and free the anterior shoulder. This makes suprapubic pressure the correct first subsequent step.
Step 4: Discarding the others: sharp hip flexion simply restates McRoberts that is already finished, 90-degree rotation of the posterior shoulder belongs to the later internal maneuvers, and emergency cesarean is reserved for failure of all conservative steps.
\[\boxed{\text{Suprapubic pressure}}\]