It's the Glucose Tolerance Test but not everybody has it - only if you have a BMI over 30 or a family history of diabetes.
I had it last time and it was fine and I have it again in 4 weeks when I'm 28 weeks. Basically they take your blood, make you drink a Lucozade type drink, sit in the waiting room for 2 hours then take your blood again. They compare the two tests to measure how your body dealt with the sugar in the drink to see whether there are signs of gestational diabetes.
That's how they do it in my area and whilst it's a bit boring, it's fine! xx