A 25-year-old woman complains of pain in her right iliac region that lasts for 10-12 days already and a menstruation delay of 7-8 weeks. Palpation detects pain in the right iliac region. Gynecological examination detects pain in the right vaginal fornix, but no enlargement of the uterus or ovaries. A right sided ectopic pregnancy is suspected. What examination method would be optimal in this case?