37 and up, my doc starts at 37 to 38 but some start at 36 and some at 40, i would ask your doc what their protocal is. And 30 weeks is wayyy to early to check unless there is a reason to check for pre term labor.
37 wks with my experience. .
Some 36, some later on, like 38, some don't check at all because it can introduce bacteria.