A 32-year-old woman, currently 28 weeks pregnant, presents to the antenatal clinic for a routine check-up. She has a history of gestational diabetes mellitus (GDM) diagnosed at 24 weeks of gestation. Her current treatment includes dietary modifications and regular blood glucose monitoring. Her recent fasting blood glucose levels have been consistently between 5.5 and 6.0 mmol/L, and her postprandial levels are between 7.5 and 8.0 mmol/L. She reports feeling well and has no symptoms of hypoglycemia. Her obstetric history includes one previous pregnancy complicated by GDM, which was managed with insulin. Her current pregnancy is otherwise uncomplicated. What is the most appropriate next step in the management of her gestational diabetes?