Popularization of Yolk Sac Knowledge

The yolk sac is the first extraembryonic structure that can be scanned by ultrasound. It can be seen in the early stages of pregnancy. The size of the yolk sac is of great significance to pregnant women and may directly affect the outcome of their pregnancy. Next, I will share with you some knowledge about the yolk sac and the importance of the size of the yolk sac to pregnant women. I hope it will be helpful to pregnant female friends.

When the pregnancy is 5 to 6 weeks, the yolk sac is found between the amniotic membrane and the chorionic fluid in the gestational sac, and a round blister-like structure appears in the gestational sac, forming a "sac within a sac" phenomenon. The yolk sac is 3 to 5 mm in size, generally less than 8 mm, and its diameter is about 1/3 of the gestational sac. Later, its proportion gradually decreases and disappears. The yolk sac is located on the ventral side of the embryo and is a membrane sac with rich blood vessels that surrounds the yolk. After the embryo develops body folds, the archenteron is clearly divided into the archenteron within the embryo and the yolk sac outside the embryo, which contains a large amount of yolk. The wall of the yolk sac is formed by the extraembryonic endoderm and extraembryonic mesoderm. At the end of the 5th week, the yolk sac of the human embryo separates from the archenteron and gradually degenerates. By the 7th week, it becomes a small sac with a diameter of less than 5 mm, remaining on the surface of the placenta. The development of the human embryonic yolk sac is also one of the phenomena of recapitulation system development.

The size of the yolk sac is usually expressed in terms of length and width, with the transverse diameter being the standard size value. The approximate number of days of pregnancy can be calculated according to this formula =〔(X+Y+Z)/3〕+25. Where XYZ represents the length, width and height of the gestational sac, in centimeters (mm).

The size of the yolk sac is closely related to the outcome of the pregnancy. Under normal circumstances, it will not exceed 8mm. The editor recommends that all pregnant mothers should check their bodies regularly and maintain a good attitude, which is beneficial to the health of the baby. I also hope that the editor’s knowledge about yolk sac will be helpful to everyone.