A 28-year-old multiparous woman at 28 weeks of gestation presents with vaginal bleeding and mild abdominal pain for 2 hours. Vital signs are stable (BP 118/76, HR 88/min). On examination, the uterus is mildly tender but not rigid. Fetal heart rate is 140/min with normal variability. Ultrasound shows a small retroplacental clot (1.5 cm) with no free fluid in the pelvis. Complete blood count shows hemoglobin 10.5 g/dL, platelet count 250,000/μL. Coagulation studies are normal. What is the most appropriate immediate next step in management?