You Are Following Up a 45-Year-Old Woman for Heavy Bleeding

You are following up a 45-year-old woman for heavy bleeding. You initiated treatment, and her bleeding has subsided. She presented a week ago with a 2-week history of heavy vaginal bleeding with blood clots. Her gynecological history revealed 1-year history of irregular bleeding, characterized by several months of no bleeding followed by 1-2 weeks of "heavy menstrual bleeding." Her physical exam, including pelvic exam, was benign. At this follow-up visit, which of the following diagnostic tests is most appropriately ordered for the investigation of this abnormal bleeding pattern?

A) MRI of the pelvic organs
B) Endometrial biopsy
C) Saline infusion sonography
D) Blood serum CA 125