1. An injection treatment design method comprising: modeling, by a computer system, fracture growth in a subterranean region, the modeled fracture growth indicating a fracture growth orientation in response to a modeled fluid pressure acting on the subterranean region; and determining, by the computer system, based on the fracture growth orientation, a target net treating pressure for fluid acting on the subterranean region during an injection treatment of the subterranean region.