A nurse is caring for a client who is at 23 weeks of gestation and has been unable to control her gestational diabetes mellitus with oral hypoglycemic therapy, diet and exercise. The nurse should anticipate a prescription from the provider for which of the following medications for the client?

A. Letrozole: Letrozole is an aromatase inhibitor used for ovulation induction in clients with infertility. It is not used to manage gestational diabetes and would have no role in glucose regulation during pregnancy. B. Lactulose: Lactulose is a laxative commonly used to treat constipation or hepatic encephalopathy. It has no glucose-lowering effects and is not appropriate for managing gestational diabetes mellitus. C. Insulin: Insulin is the treatment of choice for gestational diabetes when diet, exercise, and oral agents fail to control blood glucose. It does not cross the placenta and allows precise glucose management, making it safe and effective during pregnancy. D. Metoprolol: Metoprolol is a beta-blocker used to treat hypertension or certain cardiac conditions. It is not indicated for gestational diabetes and may affect glucose metabolism, especially at higher doses.