A 29-year-old primigravida at 9+2 weeks gestation presents with regression of early pregnancy symptoms and plateaued serum beta-hCG. Transvaginal ultrasound shows a gestational sac with irregular contour and a fetal pole with crown-rump length of 12 mm. M-mode assessment over the structure marked **A** reveals absence of cardiac activity sustained for more than 30 seconds. The yolk sac is small and degenerated. According to the Society of Radiologists in Ultrasound (SRU 2013) and RCOG criteria, what is the most appropriate diagnosis?