The glucose tolerance test (aka the GTT) is a screening test to check for gestational diabetes mellitus (GDM), a common pregnancy condition affecting about 5 percent of women. It’s usually given between 24 and 28 weeks, earlier if you’re in a high-risk category for diabetes, and involves fasting overnight and then going to a lab where a blood sample is drawn and you’re given a sugary drink. After an hour your blood will be drawn and checked again for the presence of glucose, a sugar that’s a byproduct of carbohydrate digestion which your pancreas should clear from your blood. Extra glucose in your bloodstream can damage your organs, stress your heart and lead to a dangerously large baby who will be at a higher risk for growing up obese.
The amount and type of food you ate in the days before a test and how hydrated you are can affect test results, so the presence of extra glucose after the one-hour test doesn’t necessarily mean you have gestational diabetes. In fact, only about 20 percent of the women who “fail” the GTT turn out to have GDM. So if your screening shows high glucose levels you’ll be advised to come back and take another, longer test, usually three hours.
If a second test also shows high glucose levels you’ll be considered to have GDM. Your health care provider will help you arrange to meet with a dietician to devise a healthy eating plan to control your carbohydrate intake. You’ll be advised to self-test your blood sugar levels daily, and to increase your exercise. If you can’t keep your glucose levels under control with diet and exercise alone you may need to take insulin.
The good news is that even if you have GDM if you’re able to keep your glucose levels healthy your risk of related complications during birth and pregnancy is quite low, and while being diagnosed with GDM does increase your risk of developing Type 2 diabetes later in life, gestational diabetes does go away after delivery.