From the Guidelines
To interpret the results of a 3-hour Oral Glucose Tolerance Test (OGTT) in pregnancy, focus on the blood glucose values at each time point, with diagnosis of gestational diabetes made when at least two of the following plasma glucose levels are met or exceeded: fasting ≥95 mg/dL, 1 h ≥180 mg/dL, 2 h ≥155 mg/dL, and 3 h ≥140 mg/dL, as per the Carpenter-Coustan criteria 1.
Key Considerations for Interpreting OGTT Results
- The OGTT should be performed in the morning after an overnight fast of at least 8 hours 1.
- The test involves drinking a 100-gram glucose solution, with blood drawn before drinking and at hourly intervals for three hours 1.
- The diagnosis of gestational diabetes is made based on the plasma glucose values measured during the OGTT, using the Carpenter-Coustan criteria 1.
Importance of Proper Diagnosis and Treatment
- Proper diagnosis and treatment of gestational diabetes are crucial to prevent complications for both mother and baby, including excessive birth weight, preterm birth, and increased risk of type 2 diabetes later in life 1.
- Treatment may include diet modifications, exercise, blood glucose monitoring, and possibly insulin or oral medications 1.
Timing of the OGTT
- The OGTT is typically performed between 24-28 weeks of pregnancy for women with risk factors or abnormal glucose screening results 1.
- The American Diabetes Association (ADA) recommends using the International Association of Diabetes and Pregnancy Study Groups (IADPSG) diagnostic criteria to optimize gestational outcomes 1.
From the Research
Interpreting 3-Hour Oral Glucose Tolerance Test (OGTT) Results in Pregnancy
The 3-hour OGTT is a diagnostic tool used to assess gestational diabetes mellitus (GDM) in pregnant women. The test measures blood glucose levels at four different time points: fasting, 1 hour, 2 hours, and 3 hours after consuming a 100g glucose solution.
Understanding Abnormal Values
- A single abnormal value on the 3-hour OGTT is associated with adverse maternal and neonatal outcomes, including macrosomia, large for gestational age, increased mean birthweight, neonatal hypoglycemia, and total cesarean delivery 2.
- The risk of adverse outcomes is similar to that of women with GDM, with the exception of birthweight 2.
- Isolated abnormal values at different time points (0,1,2, and 3 hours) are associated with varying risks of macrosomia and large for gestational age 3.
Diagnostic Criteria
- The American College of Obstetricians and Gynecologists (ACOG) recommends a 2-step approach for diagnosing GDM, with a 3-hour, 100-g OGTT reserved for women with an abnormal 1-hour, 50-g glucose challenge test.
- The diagnosis of GDM is based on the presence of two or more abnormal values on the OGTT 2, 4.
Clinical Implications
- Women with one elevated glucose tolerance test value are at increased risk for adverse perinatal outcomes, including cesarean delivery, preeclampsia, chorioamnionitis, and neonatal admission to the intensive care nursery 4.
- The omission of the third hour glucose measurement from the OGTT may result in a lower diagnosis rate of GDM, but may not substantially alter perinatal outcomes 5.
Preparatory Diet
- A high carbohydrate preparatory diet does not significantly affect the results of the 3-hour OGTT in pregnancy 6.