Ok, here's my pet peeves of routine interventions that are not evidence based::)
1)early cord clamping
2)routine use of pitocin(particularly in elective inductions for first time moms)
3)regular vaginal exams
6)regular suctioning and oxygen of baby right afterwards with no indication(this is changing though)
And one intervention that has shown to help with many variables and is cost effective, but is not provided automatically: labor support other than the nurse(in some studies, just having the nurse showed no difference).