When does gestational diabetes appear if it's going to?

I'm 25 weeks and 2 days, and I had the glucose-tolerance test (the one where you fast overnight beforehand and then drink the sweet stuff and then have blood test done 2 hours after that). We skipped to that test without doing the simpler one because I am overweight and have borderline PCOS, which makes me higher risk for diabetes in general.

Anyway, the result came back as normal, which I'm delighted with, because I've been worrying about it a bit.

But now I wonder: if I'm clear at 25 weeks will I be clear for good now with this pregnancy? The ob didn't suggest that another test might be needed, so I'm hoping that means that it would have shown by now if it was going to show, so I'm OK.

Does anyone know if that's right?