Is HbA1c recommended for diagnosing gestational diabetes?

• A. No; OGTT is used, and HbA1c accuracy may be affected by red cell turnover
• B. Yes; OGTT is used
• C. HbA1c is used only in second trimester
• D. HbA1c is used to screen after delivery

Answer: (A)

Gestational diabetes is diagnosed with an oral glucose tolerance test because it directly tests how the body handles a glucose load at a specific moment in pregnancy. HbA1c, while useful for monitoring average glucose over about two to three months, is unreliable in pregnancy. Red blood cell turnover increases, iron status can vary, and placental factors can alter HbA1c independently of true glycemia. These changes can make HbA1c falsely low or misleading for diagnosing GDM. That’s why the recommended approach uses the OGTT, not HbA1c, for diagnosis. Postpartum screening isn’t based on HbA1c for diagnosing GDM, so relying on HbA1c after delivery isn’t appropriate.