Apparently GD CAN occur at any time during the pregnancy, but the most likely time is 25-27 weeks (or something like that). So my endo ('cos I did have GD) said there is always a risk that they'll miss some GD cases, but I don't think it's a high enough risk that they bother re-testing people unless they show up with a whole heap of suspicious GD symptoms. I know some people on a second/third pregnancy after a PG with GD will be tested much earlier just in case and then again. Given you were all clear, I'd think it would be highly unlikely you'll be tested again. So saying, eating low GI is always a good idea anyway.