A 25-year-old pregnant fe...

A 25-year-old pregnant female presented to the emergency department with a complaint of two episodes of hematemesis and blood in the stool. She is in her 7th month of pregnancy. On examination, she exhibited pallor, a three-day history of fever, low blood pressure (80/50 mmHg), normal oxygen saturation (SPO2 98%), a temperature of 98.6°F, a random blood sugar level of 128 mg/dL, absent fetal heart sounds, and no fetal activity. The patient had a past medical history of Grade 4 esophageal varices, and the intrauterine device (IUD) was suspected. One hour after presentation, she had a vaginal delivery (IUD), and her condition is now stable. What investigation would be the most suitable for making a diagnosis in this case?