PLE-4567

Maria, a 19-year-old G1P1 who was previously treated for PID 2 years ago, was brought to the hospital due to severe hypogastric pain and vaginal spotting. She is using 3 pads per day, which are lightly soaked. Her history reveals a delay in her menses for 3 weeks now. What is the gold standard procedure for diagnosing an ectopic pregnancy?