A 28-year-old primigravida at 28 weeks of gestation presents with 300 mL of vaginal bleeding. She is hemodynamically stable (BP 118/76 mmHg, HR 88 bpm). Transvaginal ultrasound confirms placenta previa with the lower placental edge 1.5 cm above the internal cervical os. She is admitted for expectant management. On day 5 of hospitalization, she develops sudden onset of heavy vaginal bleeding (estimated 600 mL in 30 minutes) with hemoglobin drop from 10.2 to 8.5 g/dL. Fetal heart rate is 155 bpm with decreased variability. What is the most appropriate next step?