A 30-year-old pregnant woman complains of pain in her lower abdomen and mild bloody discharge from the genital tract, observed over the first 3 hours. Her last menstruation was 3 months ago. Vaginal examination detects the body of the uterus enlarged to 16 weeks of pregnancy, the external os allows inserting a fingertip, the discharge is bloody, in a small amount, contains small bubbles. Ultrasound shows a "snowstorm pattern" in the uterine cavity. What is the most likely diagnosis in this case?