A 32-year-old multigravida (G3P2) at 30 weeks of gestation is found to have gestational diabetes on routine screening. She has been on medical nutrition therapy for 4 weeks with SMBG monitoring. Her fasting glucose readings average 98–102 mg/dL and 2-hour postprandial readings average 155–165 mg/dL. She is otherwise healthy with no complications. What is the most appropriate next step?