Which test and criteria are used to screen for gestational diabetes?

• A. 75 g oral glucose tolerance test with thresholds (IADPSG) fasting ≥ 92 mg/dL, 1 hour ≥ 180 mg/dL, 2 hours ≥ 153 mg/dL; any one abnormal.
• B. 50 g oral glucose challenge test with threshold 140 mg/dL
• C. Fasting plasma glucose alone
• D. 100 g oral glucose tolerance test with two abnormal values

Answer: (C)

Screening tests in gestational diabetes are meant to quickly identify who might have GDM and who needs a full diagnostic test. The standard screening approach uses a 50 g glucose challenge test given without fasting, and we measure the glucose level after one hour. If that one-hour value reaches about 140 mg/dL or higher, it signals a higher risk and the patient should proceed to a diagnostic test to confirm whether gestational diabetes is actually present. The diagnostic test most commonly used is a 100 g oral glucose tolerance test, where two or more abnormal values (according to specific criteria) confirm GDM.

Other options describe tests that serve different purposes. A one-step 75 g glucose tolerance test with the IADPSG thresholds is used by some guidelines as a diagnostic approach, not a screening step. Relying on fasting plasma glucose alone misses many cases of GDM and isn’t used as the screening method. The 100 g OGTT with two abnormal values is indeed diagnostic, not screening.

So, the test and threshold used to screen for gestational diabetes is the non-fasting 50 g glucose challenge test with a threshold around 140 mg/dL; a positive result leads to the diagnostic 100 g OGTT.