What is the yolk sac?
Th yolk sac is something that is a normal part of early fetal development. It develops as a cavity in the blastocyst about 8 or 9 days after fertilization. It serves many functions in embryonic development, such as helping to transfer nutrients to the embryo during the second and third weeks, while uteroplacental circulation is being established; and forming early blood cells until this can be done in the liver during the 6th week. Part of the yolk sac remains to become part of the primitive gut. The yolk sac detaches from the midgut loop by the end of the 6th week and shrinks as gestation advances.
