A 28-year-old G2P1 at 28 weeks gestation undergoes a 100-g oral glucose tolerance test (OGTT). Results: Fasting 92 mg/dL, 1-hour 187 mg/dL, 2-hour 158 mg/dL, 3-hour 136 mg/dL. Using Carpenter-Coustan criteria (thresholds: fasting 95, 1-hr 180, 2-hr 155, 3-hr 140), how many values are abnormal and what is the diagnosis?

• A One abnormal value — gestational impaired glucose tolerance, not GDM
• B Two abnormal values — gestational diabetes mellitus (GDM) ✓
• C Three abnormal values — overt diabetes in pregnancy
• D Two abnormal values — requires repeat OGTT in 4 weeks to confirm GDM

Explanation

Carpenter-Coustan thresholds for 100 g OGTT: fasting 95, 1-hour 180, 2-hour 155, 3-hour 140 mg/dL. Checking each value: fasting 92 < 95 (normal); 1-hour 187 > 180 (abnormal); 2-hour 158 > 155 (abnormal); 3-hour 136 < 140 (normal). Two values exceed threshold, which meets the criterion for GDM diagnosis (≥ 2 abnormal values). GDM diagnosis requires ≥ 2 abnormal values on the 3-hour 100 g OGTT under Carpenter-Coustan criteria; no repeat test is needed.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.