What is the primary reason why an episiotomy is not performed in cases of shoulder dystocia?

The primary reason why an episiotomy is not performed in cases of shoulder dystocia is that the issue primarily revolves around the bones of the pelvis and the position of the fetal shoulders rather than being a problem related to the soft tissues of the perineum. In shoulder dystocia, the anterior shoulder becomes impacted behind the pubic symphysis, and simply making an incision in the perineum does not address the underlying mechanical issue of this bony obstruction.

Improving the soft tissue space does not lead to the resolution of the shoulder's rotational movement required to navigate through the birth canal in cases of shoulder dystocia. Therefore, resources and efforts are better directed toward maneuvers, such as McRoberts maneuver or suprapubic pressure, which directly attempt to reposition the baby’s shoulders in a way that can effectively relieve the obstruction.