Girls, I've been wrestling with this question for 13 weeks now... At 5…

Girls, I've been wrestling with this question for 13 weeks now... At 5 weeks ultrasound, they found 3 sacs, one with an embryo, another with a yolk sac, and 3 empty ones. The uterus was enlarged to 7-8 weeks. I went back for an ultrasound a week later, and they found hematomas. I had a screening at 11 weeks, and only one fetus was left. Can it really have disappeared from the sac with a yolk sac? It was indeed without an embryo... Please tell me about this from a scientific point of view ?