Undiagnosed or undetected ectopic pregnancy is a common cause of maternal death during the first trimester. Most valuable diagnostic test in a case of suspected ectopic pregnancy is:

Transvaginal ultrasonography (TVUS) has the advantage of earlier and better localization of the pregnancy, with less pelvic discomfo because the bladder is not painfully distended. The double-ring sign and the yolk sac must be identified to ensure that the pregnancy is intrauterine. When an intrauterine pregnancy is not visualized on TVUS and the hCG level exceeds 1000-2000 mIU/mL, suspicion for an ectopic pregnancy should be high. Ref: Hill M.J., DeCherney A.H. (2013). Chapter 36. Imaging in Gynecology. In A.H. DeCherney, L. Nathan, N. Laufer, A.S. Roman (Eds), CURRENT Diagnosis & Treatment: Obstetrics & Gynecology, 11e.