A 30-year-old woman presents to the emergency department complaining of severe lower abdominal pain, vaginal bleeding, and nausea. She reports her last menstrual period was 6 weeks ago and she has experienced mild cramping and spotting. A pelvic examination reveals tenderness in the adnexa. A pregnancy test is positive. A transvaginal ultrasound is performed, which shows a non-viable intrauterine pregnancy and a complex adnexal mass, suggestive of an ectopic pregnancy. What is the most common site for an ectopic pregnancy?
