A 32-year-old primigravida at 28 weeks of gestation presents to the emergency department with painless vaginal bleeding of 200 mL. Vital signs are stable (BP 128/82 mmHg, HR 88/min). Obstetric examination reveals a soft, non-tender uterus. Speculum examination shows blood pooling in the vagina. Transabdominal ultrasound confirms placenta previa (complete type, covering the internal cervical os). What is the most appropriate next step in management?