Placental Abruption

A 32-year-old G3P2 woman at 33 weeks gestation with chronic hypertension presents with sudden-onset severe lower abdominal and back pain, dark vaginal bleeding, and a rigid, tender uterus after a motor vehicle collision. Fetal heart tracing shows late decelerations and decreased variability. Transabdominal ultrasound demonstrates the finding marked **A** in the diagram—a 6 × 4 cm hypoechoic-to-isoechoic collection between the placenta and uterine wall. Which of the following is the most appropriate immediate management for this patient?