A 20-year-old woman complains of sudden onset of right-sided lower abdominal pain and bleeding per vagina. Her last normal menstrual period was 35 days ago. Her blood pressure is 90/70 mmHg and the pulse rate is 100 bpm. There is tenderness and guarding in the right iliac fossa. She denies any sexual intercourse.What is the most appropriate next step in the management?