At about 24-28 weeks gestation, you will receive a glucose tolerance test to see if you have gestational diabetes in pregnancy. Basically, it is a screening glucose challenge test for pregnancy related diabetes. In this test, you do not have to be fasting; you must only drink 50 grams of a sugary soda beverage and have your blood sugar tested an hour later.
Normal values are glucose levels of less than 140 mg/dL. If your testing results are less than this, you don’t have gestational diabetes. If the result is greater than the normal range, you need to have a second test not normally done in pregnancy.
While the first test is non-fasting, there are restrictions on what to eat during the second test, called the three-hour glucose tolerance test. In this test, you are fasting and you take a 100 gram load of glucose. Your blood sugar is tested fasting and at one hour, two hours, and three hours after the drink is given. There are no side effects to this test, but you must follow the doctor’s instructions carefully. You will not be allowed to eat or drink anything during the three hours and most doctors say you must stay in the office the entire time. Some tips to tolerating this length of time are to bring a good book or a series of magazines to read while you are having the test.
Other than being fasting, there is no preparation necessary for the three-hour test. The normal range values are different for the three-hour test. If any of the test results fall above the normal range, you have gestational diabetes and need to see a dietician and follow your glucose levels carefully at home. The biggest risk for gestational diabetes is having a baby that is too big so that it cannot fit through the birth canal. In such cases, a cesarean section may have to be undertaken or the pregnancy might have to be induced earlier than forty weeks gestation.
The One-hour Glucose Tolerance Test in Pregnancy
This is the first test you will have to test for diabetes in pregnancy. You may eat a light meal before taking the test, but you can also do it fasting if you are not hungry. Just follow the directions your doctor gives you as to what to eat and what not to eat before the screening test.
You will drink a slightly fizzy, sugary beverage that usually tastes like cola or like a lemon-lime soda. You should drink it over a five minute period of time or less. Then you must stay in the office for an hour and you cannot have anything to eat or drink after taking the glucose load. In one hour, your blood sugar will be checked. If it is under 140 mg/dL, no further testing is required unless you later show sugar in your urine test strip, which is done at every pregnancy-related visit.
If the test result is higher than 140 mg/dL, it does not mean that you definitely have gestational diabetes. It just means you have to go onto the 3-hour test to prove or disprove the diagnosis of gestational diabetes. This is a better test to see if you have gestational diabetes but the one hour screening test is usually done first because it is sensitive in picking up gestational diabetes and because it doesn’t take as long as the three hour test. Only those that fail the one hour test will need to take the three-hour test.
These tests are important in pregnancy because you might need extra care in pregnancy if you are diagnosed with gestational diabetes. If you are actually diagnosed with gestational diabetes, you need to watch the sugar intake during pregnancy and you must check your sugars several times per day. Women with gestational diabetes are often encouraged to gain less weight in pregnancy than they would otherwise be allowed to gain. This keeps the weight of the baby down so it doesn’t get too big. There is a slight risk of miscarriage or still birth in gestational diabetes so extra monitoring of fetal health will have to be done in the third trimester of pregnancy. If all goes well, you will have just a slightly larger baby that will otherwise be healthy. The gestational diabetes usually goes away but in some women, it heralds having diabetes later in life.