A 16-year-old girl presents to the emergency department complaining of fever, chills, abdominal pain, and vaginal bleeding. She gives a history of unprotected sexual activity with her 17-year-old boyfriend over the past several months. Her last menstrual period was 8 weeks ago. She reports having a dilatation and curettage procedure at an unlicensed abortion clinic recently to try to abort the pregnancy. Her temperature is 38.7°C (101.7°F), heart rate is 120/ min, and blood pressure is 100/70 mm Hg. Pelvic examination reveals cervical motion tender ness, tissue in the internal os, and foul-smelling vaginal discharge. Urine is positive for β-human chorionic gonadotropin. Which of the following is the most likely diagnosis?