A 28-year-old primigravida at 24 weeks of gestation presents for routine antenatal care. She is asymptomatic. Her BMI is 26 kg/m². She has no significant past medical history, but her mother was diagnosed with type 2 diabetes at age 45. A 75-g oral glucose tolerance test (OGTT) is performed: fasting glucose 95 mg/dL, 1-hour glucose 185 mg/dL, 2-hour glucose 155 mg/dL. What is the most appropriate next step in management?