Between weeks 24-28 most pregnant women are tested for gestational diabetes (diabetes while pregnant.) About 2-5% of expectant mothers have gestational diabetes. My mom had it with her first pregnancy (me.)
The test most women take to check for gestational diabetes is a one-hour glucose test. The way my birth center had me take it is to drink a bottle of what tastes like orange soda (which contains 50 g of glucose) with someone drawing my blood exactly an hour afterwards. If your blood contains too much glucose, then you have to take a 3-hour glucose test (also called the Glucose Tolerance Test.) This happens 15-23% of the time. My tests came back fine after the the one-hour test when I was pregnant with Karl so I figured I'd be fine this time around too.