The gestational sac is the primitive placental tissue and the yolk sac is a structure that forms during the development of the embryo in early pregnancy.
The gestational sac is a sac-like structure formed by continuous cell division after the sperm and egg combine to form a fertilized egg. The gestational sac is the primitive placental tissue, a small embryo wrapped by the amniotic membrane and vascular network. The gestational sac is the initial form of pregnancy, when the fetus has not yet formed, and the fetal heart is already beating when the fetal buds appear.
The yolk sac is a structure formed during the development of the embryo in early pregnancy. The yolk sac, on the other hand, is a structure that is formed after the embryogenesis of the body fold, when the proto-gut can be clearly divided into the intra-embryonic proto-gut and the extra-embryonic yolk sac, which contains a large amount of yolk, and the wall of the yolk sac is formed by the extra-embryonic endoderm and the extra-embryonic mesoderm.
The yolk sac is different from the gestational sac. During the development of the fertilized egg, the gestational sac is formed first, and then the yolk sac develops only gradually.