This case study describes a pregnant patient with vaginal bleeding who had a bedside endovaginal ultrasound in the emergency department (ED). The emergency physician identified a live intra-uterine pregnancy (IUP) with another structure that appeared to be a second gestational sac. The patient subsequently had an endovaginal ultrasound in the radiology department 46 minutes later. The attending radiologist described one live IUP and a subchorionic hemorrhage. Comparison of the ED and radiology ultrasound showed that the second structure, identified as a subchorionic hemorrhage, had significantly decreased in size. Endovaginal ultrasound in the evaluation of possible ectopic pregnancy is a useful bedside tool in the ED. We discuss a pitfall that can occur with endocavitary ultrasound when a twin gestation is presumed
