I know of people who have had GD who have passed the test or only failed by a tiny amount but when they started monitoring thjeir numbers they were on insulin within a week...
I have had GD 3 x now (I have no risk factors at all!) But I refuse the GTT, it is pretty poor at identifying the extent of the issue and as I said, women pass it and still have GD. I just monitored my numbers and ate as usual until they started going weird.