FCEM2-1286

A 28-year-old primigravida woman comes in with a moderate amount of vaginal bleeding and lower abdominal discomfort. She reports the bleeding to be heavier than her normal period. She is currently 9 weeks pregnant. During the examination, she experiences mild tenderness in her lower abdomen. A speculum examination is conducted, revealing an open cervical os.

What is the SINGLE most probable diagnosis?