That is an interesting observation/question. I would think that when the ovum attaches itself to the wall of the uterus it would began receiving blood but I am not sure. I never thought about it. The blood tests tell you many things
about what is going on in the body, so maybe that's why they say that the life is in the blood. They would not have known any of this back then. I am not really sure when the medical or scientist field discovered all these
things out. Interesting subject for research if a person was so inclined.