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In early pregnancy, some structures are created. They are not part of the embryo’s body , but they are there to assist you in your vital functions. So is the yolk sac, along with the other structures create conditions for the baby to develop.
What is the Yolk Bag?
The yolk sac or yolk is the first element observed in the gestational sac during pregnancy, usually from the 3rd day of gestation. It does not work for a long time, about three months, but it is of great importance for the development of the fetus.
Much of it will be incorporated into the primordial intestine from the 4th week of gestation. That is why the size of the yolk sac in the first six weeks after fertilization of the egg is much larger than the size of the amniotic cavity, along with the emerging embryo.
Why do I need a Yolk Bag?
Each stage of pregnancy has characteristics that are a very reliable indicator that the pregnancy is healthy and develops as it should. In the early stages of development, when the embryo is formed, only the yolk sac performs a variety of functions, without which the normal baby development would be impossible.
Yolk Bag Functions
- The yolk sac works to provide food to the embryo during the initial stages until the placenta takes over, which happens around the 8th week of gestation . It also acts as a system that allows blood and nutrients to circulate throughout the embryo, called the circulatory system .
- From the 18th day of the beginning of a new life in the yolk sac, the first embryonic red blood cells (erythroblasts) are formed and the capillaries begin to grow, after which the whole fetal circulatory system has been formed.
- From the 28th day, the walls of the yolk sac produce the first germ cells, which will later move to the embryonic gonads. It is important to say that, at this moment, the eggs of a future girl are formed . If, at this time, the mother has suffered or suffers severe stress – the formation of eggs will occur incorrectly and, in the future, an adult woman may suffer from infertility.
- Until the 6th week, the yolk sac plays the role of “ primary liver ” and produces proteins that are very important for the development of the embryo, such as alpha-fetoprotein.
The yolk sac is also actively involved in metabolic processes, the formation of immunity and replenishes discharges from the fetus.
Is it possible to see the yolk sac on ultrasound?
On ultrasound, the yolk sac is visible from the 5th to the 12th week of pregnancy. If the doctor does not see the yolk sac, this condition is considered unfavorable, as it can be a sign that the pregnancy can stop progressing at any time. The premature disappearance of the yolk sac is also an unfavorable sign.
Normally, the yolk sack should have the following dimensions:
- less than 5.5 mm at 5-10 weeks;
- more than 2 mm at 8-12 weeks.
This is because the diameter of the yolk sac increases exponentially between the 5th and 11th weeks of gestation, decreasing soon afterwards, in accordance with the growth of the fetus.
At the end of the first trimester , the fetus is fully formed and passes through the placental circulatory type . The yolk sac becomes redundant and is reduced, that is, it is reduced to the point that it is no longer seen on ultrasound.
Until the end of the pregnancy it remains in the form of a small body, a little oval , whose diameter varies from 1 mm to 5 mm at the base of the umbilical cord . If the yolk sac is reduced before the right time, that is, when all the organs of the fetus have not yet been formed, the pregnancy will not develop correctly.
The embryo will not be able to evolve to a new stage of development, and it will not become a fetus. This is what often leads to a non-viable pregnancy and a miscarriage.
What happens if the yolk sac is not visible?
If the yolk sac is not visible between the 5th to the 11th week of gestation, there are several hypotheses that can be taken into account:
- Miscalculation of conception – Perhaps the pregnancy has not been properly identified and is less than 6 weeks old (up to 6 weeks the yolk sac is usually not visible).
- Ultrasound can determine the heart rate of the embryo (7 weeks) and the embryo is visible. However, if no yolk sac is seen after 7 weeks, it may result in termination of pregnancy.
- Unfavorable prognosis – The woman should undergo a new ultrasound, preferably transvaginally with the high resolution device, to check for the presence or absence of a yolk sac.
- After the 12th week, normally, if the yolk sac is not identified, it means that the fetus has started to receive nutrients through the placenta.
What Are Embryonic Attachments?
Like the yolk sac, embryonic attachments are temporary structures that are created to give the baby conditions to develop correctly, during its period inside the belly.
Are they:
- Yolk sac;
- Amniotic pouch or amnion;
- Allantois;
- Chorion and
- Placenta.
Or What Does Irregular Gestational Sac Mean?
During the first trimester, one of the items for checking the gestational sac is its contour, because in the case of an irregular shape, the risk of bag detachment and miscarriage is greater.
In these cases, the pregnant woman should remain at rest and use the drugs prescribed by the doctor, so that the gestational sac returns to normal and the pregnancy develops correctly.
See Also: Detachment of the Gestational Sac – How to Detect and Treat
My name is Dr. Alexis Hart I am 38 years old, I am the mother of 3 beautiful children! Different ages, different phases 16 years, 12 years and 7 years. In love with motherhood since always, I found it difficult to make my dreams come true, and also some more after I was already a mother.
Since I imagined myself as a mother, in my thoughts everything seemed to be much easier and simpler than it really was, I expected to get pregnant as soon as I wished, but it wasn’t that simple. The first pregnancy was smooth, but my daughter’s birth was very troubled. Joana was born in 2002 with a weight of 2930kg and 45cm, from a very peaceful cesarean delivery but she had already been born with congenital pneumonia due to a broken bag not treated with antibiotics even before delivery.
