The first organ that feeds the fetus is the yolk sac. The norm or, more precisely, the optimal time of appearance is 15-16 days of development of the ovum. This substance is formed from the endoblastic vesicle, which is a derivative of the embryoblast. This small formation, which is in direct contact with the fertilized egg, is unique in its composition and functions.
An interesting fact is that it is the yolk sac that gives rise to the formation of blood cells and the small capillary network. From 18-20 days of development of the fetal egg, a small blood mesh can be found in it.
Thus, this organ is one of the most important for the future baby. Indeed, until the placenta with a dense circulatory network is formed, the embryo will receive all the nutrients from the vitelline formation.
By the 30th day of development, the yolk sac transports primary germ cells to the embryo - the baby's reproductive system begins to form. Many people think that it is at this time that it is decided who will be born, a boy or a girl. However, young parents need to know that the baby’s gender was decided at the time of fertilization, and at all other stages of development only organs are formed in accordance with the genetic information.
Numerous functions of the primary feeding organ do not end there. In addition, before the 6th week of embryo development, the yolk sac also performs the function of the liver, or rather synthesizes proteins: alpha-fetoprotein, transferrins, alpha2-microglobulin.
It must be remembered that this organ is also a kind of fetal shell, until the moment when its immune system will not be able to fight possible pathogenic microorganisms itself. The fact is that the primary organ of the fetus can independently produce macrophages in the fight against infection. Thus, it protects the fertilized egg from negative external influences.
Such a system of protection and nutrition of the fetus does not work very long, by the end of the first trimester, the yolk sac degrades and turns into a small umbilical formation. By this time, the formed placenta and other organs of the fetus take on all its functions.
It must be said that if, for some reason, the yolk formation begins to regress before the placenta or other important formations form, then a miscarriage or intrauterine death of the fetus is possible . That is why there are certain time intervals when it is necessary to undergo ultrasound.
How can I detect the yolk sac and determine its functionality?
Women who are preparing for the birth of a baby have probably already read in the literature that with ultrasound, the yolk sac can be seen only from the 6th week of fetal development, and in some cases a little later. This may be due to the peculiarity of the location of the ovum or the sensitivity of the equipment.
If you are told by ultrasound that the yolk sac is not visualized, you do not need to panic right away. Listen to the doctor to the end. Surely he will explain everything to you.
There are many options for pregnancy pathology in which the bag is reduced too early, or it is not sufficiently developed. A woman should understand that even if it is possible to maintain such a pregnancy, then the likelihood of developing defects in such a baby doubles.
I must say that monitoring the development of yolk formation before 12 weeks of pregnancy can tell you about how the fetal development will proceed and what complications doctors and parents may face.
There is such a thing as “frozen pregnancy” - this is the pathology of the yolk sac, in which it is small and non-functional. The fetus reaches a certain stage of development, and for the further growth of nutrients it is already not enough. In such a situation, it is necessary to perform a cleaning of the uterine cavity together with hormonal therapy.