Are these statements correct ? When a woman ovulates, her egg remains separate from her body and is protected by a shield that will allow only a single sperm cell to pass. Mother and child do not share the same blood supply, in fact they can have different blood types. At conception there is no blood, just a single cell which is a fertilized egg. This begins doubling itself and forms a yolk sac (similar to what s in a chicken egg) for short-term nutrition. Then it implants into the uterine wall and grows a placenta . The fetus makes its own blood from its liver and spleen , and starting at 21 weeks, from its bone marrow