A 26-year-old pregnant woman at 26 weeks gestation is undergoing a 1-hour glucose challenge screening. She drinks the 50-gram glucose solution, and her blood glucose is measured 1 hour later at 150 mg/dL. Which of the following is the most appropriate next step?

A. Reassure the patient that the result is normal; no further testing is needed is incorrect because a 1-hour glucose screen result ≥140 mg/dL is considered abnormal and requires further evaluation. Simply reassuring the patient without follow-up could miss a diagnosis of gestational diabetes mellitus (GDM). B. Begin insulin therapy immediately is incorrect because insulin therapy is not initiated based on a screening test. A diagnostic test must confirm GDM before pharmacologic management is started. Initiating insulin without confirmation could be unnecessary and potentially harmful. C. Schedule a 3-hour oral glucose tolerance test for diagnostic confirmation is correct because the 1-hour 50-gram glucose challenge is a screening tool. A result of 150 mg/dL is above the typical screening threshold (≥140 mg/dL), so the next step is a diagnostic 3-hour, 100-gram oral glucose tolerance test (OGTT). This test measures fasting, 1-hour, 2-hour, and 3-hour glucose levels to confirm gestational diabetes before treatment is initiated. D. Repeat the 1-hour test tomorrow is incorrect because repeating the same screening test does not provide a definitive diagnosis and may delay appropriate diagnostic evaluation and management. The 3-hour OGTT is the standard next step after an abnormal 1-hour screen.