Q. A 23-year-old primigravida with 12 weeks of gestation presents to the emergency department for vaginal spotting and low back ache from the morning. Her temperature is 37°C (98.6°F), pulse is 84/ min, and blood pressure is 120/70 mm Hg. A pelvic examination shows a closed cervical os with no conceptional tissue. Cervical motion tenderness is absent. A transvaginal ultrasound shows an intrauterine viable fetus of 14 weeks gestational age with a heart rate of 150 beats per minute. What is the most likely diagnosis for this patient?