Diagnosis of Gestational Diabetes Mellitus Using Carpenter-Coustan Criteria

Diagnostic Approach

The American College of Obstetricians and Gynecologists (ACOG) recommends a two-step approach for diagnosing gestational diabetes mellitus (GDM), starting with a 50-g glucose load test (GLT) at 24-28 weeks of gestation, followed by a 100-g oral glucose tolerance test (OGTT) if the initial screening is positive 1, 2
The 100-g OGTT should be performed after an overnight fast of at least 8 hours, with blood samples collected at fasting and at 1, 2, and 3 hours after glucose load 1, 2, 3
Diagnosis of GDM is made when at least two of the four plasma glucose levels are met or exceeded according to the Carpenter-Coustan criteria: fasting 95 mg/dL, 1-hour 180 mg/dL, 2-hour 155 mg/dL, and 3-hour 140 mg/dL 1, 2, 5, 6

GDM diagnosed by Carpenter-Coustan criteria is associated with increased risk of adverse maternal and fetal outcomes, including macrosomia and gestational hypertension 1
Women diagnosed with GDM have a markedly increased risk for later development of diabetes, generally type 2 diabetes, after delivery 7

The Carpenter-Coustan criteria are more sensitive than the older National Diabetes Data Group (NDDG) criteria, but less sensitive than the one-step approach using IADPSG criteria (75-g OGTT) 2, 5
The American Diabetes Association (ADA) recommends the IADPSG criteria, while ACOG continues to support the two-step approach with Carpenter-Coustan criteria 2, 4, 5, 6

The choice between the one-step IADPSG approach and the two-step Carpenter-Coustan approach involves considerations of healthcare resources, as the one-step approach identifies more women requiring treatment but may "medicalize" pregnancies previously considered normal 2, 5