Long story short - it was discovered via a scan one day prior to my due date that my baby was 98th centile.
I was booked in for an induction for this reason, and one of the concerns was that I may have had undiagnosed GD. I was never offered a GTT during my pregnancy, even though I'm 36. For what it's worth, I did have the test with DC1 and it came back clear.
Anyway, I had DC2 - she weighed 9lb 4oz, so was definitely big, but I didn't hear any more re the GD. Can I assume I didn't have GD, or could it possibly be that I did but was just lucky that DC2 wasn't affected in any way?
As an aside, DH and I are both tall and well built (though not fat/overweight), so a big baby wasn't altogether unexpected. DC1 was 6lb 13oz, which was much more surprising.