The word "gestational" means during pregnancy, which means that most people won't have diabetes after delivering their baby. It only happens during pregnancy due to hormone changes the insulin level from the pancreas of that patient, who cannot handle the sugar so well. In the 3rd trimester, certain hormones rises and this can cause diabetes risk to increase so this screening test is usually done during the 3rd trimester. It is due to the body not being able to metabolize sugar quickly enough so that's why does blood sugar level goes up. The most important thing about gestational diabetes is that it has a pre-diabetes stage called impaired glucose tolerance stage. It means you can't handle sugar well but you're not diabetic yet. You need to pick this out early and routine screening test for patients without any family/personal history of diabetes or giving birth to a big baby will do this during the 3rd trimester. However, if you have any of these problems on top of your baby being bigger than average and your water level being higher than the average, we may want to this test earlier and can be repeated more than once. Generally, screening is from 24 weeks onwards and it is critical to pick this up early during the non-diabetic stage so that if you have impaired glucose tolerane, it is very easy to manage - the doctor will put you under a 1800 calories diet and teach you how to eat while reducing sugar content so that your body would not be too stressed to handle high sugar content. If that doesn't work and sugar levels by your blood test remains high, then we have to teach you how to use insulin to inject yourself to bring the sugar down and normally when the person is checked to have impaired glucose tolerance or diabetes, you're supposed to do your home glucose monitoring yourself. You must monitor every day to make sugar levels are within satisfactory range otherwise it can affect the growth of your baby (too big or not well).