A 31-year-old woman presents to the emergency depament because of two days of abdominal pain without vaginal bleeding. Pelvic examination reveals a closed cervical os and right adnexal pain. The serum beta hCG level is 9,000 mIU/mL. An endovaginal ultrasound demonstrates no intrauterine gestational sac. Which of the following is the most likely diagnosis?

The primary use of pelvic ultrasonography in women with lower abdominal pain, vaginal bleeding, and a positive pregnancy test is to establish the diagnosis of intrauterine pregnancy (IUP). Transvaginal ultrasound should visualize an IUP when the serum beta hCG level is more than 1,200 mIU/mL. If an IUP is not present, then the pregnancy lies outside of the uterine cavity, the patient has just had a miscarriage, or the pregnancy is less developed than menstrual dates indicate. The absence of vaginal bleeding and the closed cervical os suggest that an incomplete aboion is unlikely, but place this patient at high risk for ectopic pregnancy. Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 10. Ectopic Pregnancy. In F.G. Cunningham, K.J. Leveno, S.L. Bloom, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.