Sarah they will class almost that differs from a "normal" pregnancy as high risk. Elevated BP, GBS +ve, Large baby, Small baby, etc. It would depend a lot on the hospitals policy.
This is what I was told with my first baby.

Basically that if you're having a "normal pregnancy with no complications", and no problems in any previous pregnancy with all normal births - then you're low risk.

Anything else - ie. a health issue like GD or high BP in your current pregnancy, previous c/s, problems in previous pregnancy - you become high risk. It literally only takes one "issue" to push you into this category