GDM Diagnosis
The first sign that you've developed GDM may be glycosuria, or the appearance of glucose in your urine. Many pregnant women normally spill a small amount of glucose into the urine, but if your doctor detects significant glycosuria during a routine urine test, he may order a plasma glucose test to measure the level of glucose in your blood.
A level of 126 mg/dl (7.0 mmol/l) or higher if you had been fasting at the time of the blood test, or 200 mg/dl (11.1 mmol/l) or higher if you were not, represents hyperglycemia (high blood sugar) and gestational diabetes. However, you must have your blood retested on a subsequent day to confirm that diagnosis.
Without any obvious signs or symptoms of high blood sugar that suggest GDM, a glucose challenge and/or an oral glucose tolerance test (OGTT) will be performed.
Essential
The National Institutes of Health recommends that women with two or more risk factors should be tested as soon as they become pregnant, and again between 24 and 28 weeks of pregnancy. Women with a single risk factor can wait until the 24th week to be tested.
The Glucose Challenge
The glucose challenge is aptly named, because it is indeed a challenge to drink the 50 grams of sugary-sweet glucose beverage that you must consume as part of the test. One hour after you drink the glucose solution, your blood is drawn. If your serum glucose levels are 130 mg/dl or higher (7.2 mmol/l), it's an indication that your insulin may not be doing the job it's supposed to, and an oral glucose tolerance test is ordered.
Fact
According to the ADA, women who are obese (a BMI of over 30) and have GDM may benefit from restricting their carbohydrate intake to 35 to 40 percent of their total calories. Studies have shown this can improve fetal outcomes and reduce hyperglycemia in the mother.
The Oral Glucose Tolerance Test (OGTT)
If it was a challenge to drink 50 grams of glucose, it is a true test of your tolerance (not to mention your intestinal fortitude) to drink the 75 to 100 grams of the stuff required for the OGTT. This test is usually administered in the morning because it requires a minimal eight-hour fast before it is performed. Your blood is taken before you are given the solution to drink, and then blood is drawn at periodic intervals afterward.
For the 100-gram OGTT, considered the most well validated of the two tests, blood is drawn at one hour, two hours, and three hours later. If your doctor gives you the 75-gram OGTT, blood is only drawn at the one-hour and two-hour intervals. For both tests, diagnostic thresholds are the same.
Fasting levels of 95 mg/dl (5.3 mmol/l) or higher before the test, 180 mg/dl (10.0 mmol/l) or higher at one hour, 155 mg/dl (8.6 mmol/l) or higher at two hours, and 140 mg/dl (7.8 mmol/l) at three hours suggest GDM. If two or more of these readings are elevated, GDM is diagnosed.
