Could you ask to see if they offer an alternative to the x-ray for pregnant people. I know sometimes they use ultrasounds instead, but I think the shoulder might be a bit hard for that. And ask how necessary it is. At the end of the day its your decisions, they use to use x-ray's if you were having multiples back in the early 1900's at least. They might also do a lower millirad x-ray on you, if they need to do it.