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When the yolk sac disappears. Yolk sac during pregnancy: norm, size by week

The conception and birth of a new living being is truly the greatest miracle in the world. Mammals have a yolk sac, fish have eggs, reptiles and birds have eggs. All these elements allow such a unique action as the birth of a child to be realized.

Evolution brought many changes in the world of living beings. The way babies are born is constantly changing. But every time, at a new stage in the development of the world, evolution introduced some kind of addition. With the advent of such a class of creatures as mammals, a new way of giving birth to children arose - live birth. In this case, the embryo did not arise from an egg, as before, but developed and grew up to a certain age in the mother's womb. It was at this time that the yolk sac appeared.

general description

The yolk sac is perhaps the main organ in the life of a future person. It is he who appears in the embryo in the first stages of its existence. Scientists attribute it to the germinal, or, in other words, to the larval, organs of the embryo.

The prototype of the bag can be considered the yolk of a bird or reptile egg. If you carefully consider a chicken egg, you can divide it into two parts: the yolk and protein. It is a huge fertilized cell. The task of the yolk is to supply the embryo and the future embryo with all the necessary nutrients, while the protein serves as a reservoir of water and essential amino acids, at an early stage it protects the embryo from external stimuli along with the shell.

In viviparous, the embryo develops in a special organ - the uterus - and until the placenta is fully attached and the umbilical cord is formed, the embryo is not able to eat with the mother. In this case, the yolk sac performs the function of a kind of digestive system and an element for providing nutrition.

In mammals and humans at the stage of the embryo, the yolk sac can be perceived as a kind of digestive system. It allows you to absorb nutrients that come to the embryo from the yolk, as well as transport the necessary compounds for growth and development through the bloodstream, thanks to a developed capillary system. In humans and many animals, in the course of evolution, the yolk sac has lost its main function - the digestion of food for the embryo - and has become an important organ for the formation of the circulatory system.

The human organ

After the embryo is fixed on the walls of the uterus, its very rapid development begins. Embryo growth is a real miracle of nature. After birth, no creature is able to develop as quickly as the fetus in the mother's womb.

Within a few weeks after conception, an endoblastic vesicle gradually forms at the site of the merged sperm and egg. He becomes a kind of "prototype" of the future human being. A few weeks later, the yolk sac begins to form from the endoblastic vesicle. It will not last long enough - its "life" takes no more than three months, but without it the fetus will not be able to form normally.

The yolk sac is referred to the so-called provisional organs. They exist only temporarily. Their function is to replace the embryo with those organs that an adult has, but have not yet formed in the embryo. In addition to the yolk sac, the following provisional organs are known:

  1. 1. Amnion, whose task is to form an aquatic environment in which a future person could fully develop.
  2. 2. Chorion. It is practically an external organ of the embryo. Since the child must attach to the walls of the uterus, he needs to "bypass" its mucous protection, and the chorion helps the embryo in this.
  3. 3. Placenta. It is an important provisional human organ. It is he who helps the future person breathe, eat, excrete waste products, grow and develop before birth. The placenta is a reliable protector of the child and accompanies him until the birth.

The main task of the yolk sac in the development of the embryo is the formation of the primary circulatory system and blood vessels. Already on the 15th day after conception, the gradual formation of the very first human capillaries begins in the walls of the organ. A month after fertilization, the yolk sac temporarily becomes the main reproductive organ of the embryo: on the 29th day of the existence of the embryo, the first cells are released that have an impact on the formation of the sex of the future person.

The yolk sac has gradually lost its digestive function, which it was endowed with in birds, fish and reptiles. In the human body, he was able to become a prototype not only of the circulatory system, but also of most organs.

Functions of the yolk sac

What is the yolk sac during pregnancy? In the first 3 months of embryonic development, this is perhaps the most important organ. Starting from the 6th week and ending with the period of the first trimester, the yolk sac is able to replace most of the internal systems of an adult human embryo.

What organs are represented by the yolk sac? Among them:

  1. 1. Liver. Around week 6, it begins to produce alpha-fetoprotein, transferrins, and alpha2-microglobulin. These proteins are vital for the normal growth and development of the embryo. The yolk sac is also called the primary human liver.
  2. 2. Sexual. By the end of the first month of development, the first germ cells appear in the body of the embryo with the help of a sac. If a girl is being formed, then it is at this time that her eggs develop. During this period, any stress is dangerous for the expectant mother, because due to a violation of the development of the fetus, her daughter may become infertile.
  3. 3. Kidneys and metabolic systems. One of the important functions of the yolk sac is excretory. At this time, it is a prototype of the kidneys, which function to purify the blood and remove excess fluid and dangerous toxins from the body.
  4. 4. Immune system. It begins to be laid in the body of a future person quite early, but at the same time it is not able to withstand external threats. The yolk sac perfectly protects the embryo from any attacks from the outside.
  5. 5. Spleen. The organ allows the formation of macrophage cells in the body, the task of which is to monitor the “order” inside a small organism. In addition, do not forget about the main function of the yolk sac - the formation of blood cells and blood vessels.

At the end of the first trimester, when the fetus is 3 months old, all the main organs and systems are already laid in its body. They allow a small embryo to function like an adult. At this time, the need for a yolk sac disappears. After the expiration of its term, the body begins to reduce. Its dimensions change and sharply decrease. But it doesn't disappear completely. It becomes like a small cyst and is located at the base of the umbilical cord of the child throughout the pregnancy until the birth itself.

Developmental pathologies

The formation of the yolk sac is the most important stage in the growth of the embryo. Even minor disturbances in its development can lead to mutations in the fetus and even to a missed pregnancy. The doctor can detect any pathology of the organ with the help of ultrasound. The first examination of a woman in order to establish conception should be carried out using an ultrasound machine. This allows you to assess the size, degree of development of the organ and its possible pathologies.

There are the following pathologies of the yolk sac:

  1. 1. Disruption of functioning. At the same time, this provisional organ ceases to perform its main functions: it does not form blood, does not carry out metabolic and immune-protective processes. Some time after the dysfunction of the organ, the fetus dies and spontaneous abortion occurs. If an abortion does not occur, we can talk about a missed pregnancy. If it continues to develop, the fetus may have a number of the broadest and life-incompatible pathologies. The causes of the condition can be chronic diseases of the mother or ailments received during pregnancy, hormonal characteristics, severe stress, injuries, etc.
  2. 2. Lack of visualization. After 6 weeks, the fetus becomes noticeable and may appear on ultrasound. 10 weeks after conception is the optimal time for an ultrasound examination. But in some cases, even for a fairly long time, the yolk sac may not be visualized. If the fetal egg is in the uterus, and the organ and the embryo are not completely visible, we can talk about the absence of pregnancy.
  3. 3. The organ is larger than the statistical size. An increase in the sac cannot be attributed to pathologies of fetal development, rather, to developmental features. The size of the organ can be affected by the sexual health of the mother, her illness at the beginning of pregnancy, stress and physical fatigue, the use of certain medications, and even the ecology of the place of residence.
  4. 4. Underdevelopment. Previously, such a pathology in most cases ended fatally for the fetus or had detrimental consequences for its further healthy growth. Modern medicine conducts special hormonal therapy. The underdevelopment of the yolk sac occurs due to a lack of progesterone in the body. Hormonal preparations make up for this deficiency and allow pregnancy to proceed normally.

Diagnosis using an ultrasound machine

The most important ultrasound during pregnancy is the first. It is carried out up to 12 weeks during the 1st trimester of a woman's pregnancy. During this ultrasound of the fetus, it is impossible to determine the sex and possible size of the child during childbirth, but the diagnosis at this time helps to find out about possible developmental abnormalities and dangerous genetic diseases.

With the help of ultrasound, the doctor can diagnose the pathology of the development of the yolk sac or violations of its functioning during a missed pregnancy. At this time, it is necessary to have an abortion, since a fetus that has stopped developing carries a mortal danger to the mother.

Most of all, the provisional organ is noticeable by 6 weeks after conception. It was at this time that its parameters, in accordance with the size of the unborn child, are greatest. By 6 weeks, the size of a human organ reaches 5 mm. In the future, they may increase, but the yolk sac will not be noticeable as before, due to the sharp growth of the embryo itself.

During the development of the fetus in the first trimester, the size of the provisional organ gradually decreases, which is clearly visible on an ultrasound examination of the fetal egg. After a while, the organ becomes like a kind of bubble. This suggests that the body of the future person no longer needs it.

By the 12th week of pregnancy, the pouch gradually begins to disappear, but does not disappear completely. It is literally "drawn" into the child's body cavity and becomes a small cyst. At the beginning of the second trimester, the size of the organ is so small that it is no longer possible to determine its position using ultrasound.

The disappearance of the yolk sac indicates that the embryo is carefully entrenched in the mother's body and provides nutrition and respiration through the umbilical cord and placenta.

The yolk sac is formed simultaneously with the amnion from the extraembryonic endoderm in the form of a yolk vesicle, which gives rise to the epithelial lining, and the adjacent layer of the extraembryonic mesoderm (mesenchyme), which forms the connective tissue basis of the organ. The human yolk sac does not contain yolk, but is filled with a liquid containing proteins and salts. Unlike birds, it does not play a significant role in providing nutrition to the fetus (the nutrition of the human fetus comes from the mother's blood). It performs the role of the first hematopoietic organ: the first blood vessels are formed from its mesenchyme, and inside them - blood cells (intravascular hematopoiesis). In the endoderm of the yolk sac, primary germ cells (gonoblasts) appear, which then migrate to the rudiments of the sex glands. After the formation of the trunk fold, the yolk sac remains connected to the intestinal tube by a small yolk stalk. Starting from the 7th - 8th week of embryogenesis, the reverse development of the yolk sac is observed. The remains of the latter can be found in the umbilical cord in the form of a narrow epithelial tube.

Allantois

Allantois is formed on the 16th day of embryogenesis in the form of a finger-shaped outgrowth of the intestinal endoderm, which, going to the amniotic stalk, is surrounded by extraembryonic mesenchyme. In birds, it performs the function of a urinary sac (it accumulates excretion products of the embryo that cannot be released into the environment due to the shell). In humans, it does not reach significant development and serves to conduct blood vessels from the embryo to the chorion. Their thinnest branches, together with the mesenchyme, penetrate into its villi. Through the vessels of allantois at the early stages of embryogenesis, the functions of nutrition, gas exchange and excretion of the embryo are carried out. Starting from the second month, the allantois is reduced and remains in the form of a strand of cells in the umbilical cord along with the reduced yolk sac.

Chorion

The chorion, or villous membrane, is found only in placental mammals and humans. It is formed at the 2nd week of human development, when the extraembryonic mesoderm grows to the trophoblast, forming secondary villi with it. At the beginning of the third week, blood vessels grow into the villi of the chorion, and they are called tertiary villi. Further development of the chorion is associated with the formation of the placenta.

Placenta

The placenta is the organ of communication between the fetus and the mother. It performs all the functions necessary for the development of the fetus. Respiratory, trophic, excretory functions are provided due to the fact that oxygen and nutrients enter the blood of the fetus through the placenta from the mother's blood, and in the opposite direction - carbon dioxide and metabolic products.

The endocrine function consists in the production of hormones that regulate the development of the fetus and the course of pregnancy: chorionic gonadotropin, placental lactogen, progesterone, estrogen, melanotropin, corticotropin, somatostatin and others. The protective function of the placenta is the passive immunization of the fetus with maternal immunoglobulins. At the same time, the placenta provides an immune barrier between the mother's body and the fetus's body. Many micro and macro elements, vitamins A, C, D, E, etc. are also deposited here.

The human placenta is formed from the 3rd to the 12th week of embryogenesis. It distinguishes between the fetal and maternal parts. The fetal part is represented by a chorionic plate, from which villi extend. The maternal part includes a part of the mucous membrane of the uterus, called the basal plate.

The chorionic plate and villi of the fetal part of the placenta are formed by loose fibrous connective tissue covered with epithelium - cyto- and symplastotrophoblast. Part of the villi reaches the basal plate of the maternal part of the placenta and attaches to it, forming anchor villi. Stem villi with their branches form structural and functional units of the placenta - cotyledons, the total number of which reaches 200. Cotyledons are separated by septa extending from the basal plate of the maternal part of the placenta. The basal lamina is the deep layer of the sheath of the endometrium. Here, decidual cells are found in large numbers - large, glycogen-rich cells with oxyphilic cytoplasm and large nuclei. Their participation in the immune response and production of hormones is supposed.

In humans, the placenta is discoidal in shape, and in relation to the chorion to the mucous membrane of the mother, it is hemochorial. The last name is due to the fact that the chorion receives oxygen and nutrients directly from the mother's blood, located in the lacunae of the mother's mucous membrane: "the villi of the chorion bathe in the mother's blood."

A hemochorial (placental) barrier forms between the blood of the mother and the blood of the fetus. It consists of symplastotrophoblast, cytotrophoblast, basement membrane of the epithelium, connective tissue of the villi, basement membrane of the fetal vessels, endothelium of the fetal vessels. By the end of pregnancy, the trophoblast becomes very thin or disappears, being replaced by a fibrin-like oxyphilic mass, consisting of plasma coagulation products and trophoblast decay - fibrinoid. Due to the placental barrier, normally foreign substances, bacteria do not penetrate into the blood of the fetus. However, it is not an obstacle to viruses, alcohol, nicotine and a number of other substances that are dangerous for the fetus, especially in the first 3 months of pregnancy, as they are not metabolized, but accumulate in its tissues and organs, as a result of which they can cause violations of embryonic development and deformity. .

Many pregnant women are interested in questions about what functions the yolk sac performs, what it is and when it occurs. After all, it is no secret to anyone that this is an extremely important element that ensures the normal development of the embryo.

- what is this?

During an ultrasound examination in the early stages of pregnancy, the doctor pays attention to the size and development of this particular structure. The yolk sac is a special one that is formed in the initial stages of pregnancy and performs extremely important functions in the first months. It is located in the region of the umbilical cord and at first is closely connected with the embryonic intestine. This formation is formed from mesoderm cells and has the shape of a ring with thin walls.

Main functions of the yolk sac

In fact, this education is extremely important. At the initial stages of development, the embryo and the yolk sac are closely related. First, this structure is a source of nutrients. Secondly, the yolk sac is actively involved in the process of respiration.

Around the eighteenth day of pregnancy, the first red blood cells begin to form in the yolk sac. This structure also ensures the formation of the first capillaries, from which the circulatory system of the fetus will develop in the future.

On the 28th day, the first germ cells are formed in the walls of the sac, which subsequently become the basis for the development of the gonads and the reproductive system of the child. In addition, during the first six weeks, the yolk sac performs all dangerous substances and toxins in its tissues.

As you can see, this formation is extremely important for the normal development of the fetus. If the yolk sac does not function normally, then this threatens to spontaneously terminate the pregnancy.

Where does the yolk sac go?

Every expectant mother knows that the vital activity of the fetus directly depends on the functioning and condition of the placenta. But where does the yolk sac go? During the first three months, the embryo and placenta have time to fully form. At this stage, the formation of the placental type of blood circulation is completed, and the yolk sac is no longer needed. Its tissues are gradually reduced. Until the end of pregnancy, this formation remains in the form of a small cyst located near the umbilical cord.

Is an enlarged yolk sac dangerous?

Since this structure is very important, it is quite natural that it is examined during an ultrasound examination. You can see it starting from the sixth week from conception. The yolk sac can no longer be examined using ultrasound.

At 5-10 weeks, the size of the bag should not exceed 5.5 millimeters. But in women, the size of this formation, as a rule, is about 2 mm.

But sometimes the doctor notices that the yolk sac is enlarged. What does this mean and how dangerous is it? In fact, any deviation from the norm may indicate a threat to pregnancy. Naturally, this is not a definitive diagnosis, as other, additional studies are needed. For example, an enlarged yolk sac may be due to diet, certain medications, or extreme stress. In any case, with similar ultrasound results, it is necessary to poison yourself with a gynecologist. Only a specialist knows why the yolk sac may be enlarged, what it means and whether special treatment is required.

The yolk sac is a germinal organ that contains a supply of nutrients for the embryo. The yolk sac persists throughout the first trimester and resolves on its own after 12 weeks. The shape and size of the yolk sac is one of the most important indicators of the course of pregnancy in its earliest stages.

Origin

The yolk sac is formed from a special structure - the endoblastic bladder - on the 15-16th day of embryo development (or on the 29-30th day from the last menstruation). During this period, a woman may not yet be aware of her changed status, and only a delay in menstruation indicates a possible conception of a child. The yolk sac develops along with the fetal egg and other structures of the embryo according to a program set by nature. Any deviation from the genetically programmed rhythm can lead to termination of pregnancy.

The yolk sac is a closed ring located inside the chorionic cavity. It functions for a short time - only 12-14 weeks. At the beginning of the second trimester, the yolk sac begins to decrease in size. After 14 weeks, the formation disappears without a trace, having fulfilled all the functions assigned to it.

The role of the yolk sac

The yolk sac is a temporary (provisional) organ, but without it, the normal course of pregnancy and the development of the embryo are impossible. In the early stages, the size of the yolk sac exceeds the size of the embryo and amniotic cavity. The yolk sac actively grows from 6 to 12 weeks of gestation, after which it gradually decreases in size and completely disappears.

On the 18-19th day from conception, the yolk sac becomes the focus of hematopoiesis. In its walls, areas of erythropoiesis are formed, and the first red blood cells are formed. In the future, an extensive network of capillaries is formed here. Primary erythrocytes, leaving the yolk sac, enter the circulatory system of the embryo and are carried with the bloodstream throughout the body.

From the 28th day from the moment of conception, the yolk sac begins the production of the primary germ cells of the embryo. Subsequently, germ cells migrate from the yolk sac and enter the anlages of the gonads (sex glands). 4-5 weeks of pregnancy is an important stage in the development of the reproductive system of the fetus. Any negative effects during this period (infections, radiation, medication) can disrupt the formation of the gonads of the embryo and cause infertility.

From the 2nd to the 6th week of pregnancy, the yolk sac acts as a liver for the embryo. In the walls of the yolk sac, important proteins and enzymes are synthesized that are necessary for the normal development of the whole organism. In particular, AFP (alpha-fetoprotein) is produced here. In the circulatory system of the fetus, AFP binds to PUFAs (polyunsaturated fatty acids) and transports them to all cells and tissues. AFP also suppresses the immune response to newly synthesized proteins, allowing metabolic processes to take place in the right rhythm.

Other functions of the yolk sac:

  • regulation of the fetal immune system;
  • hormone synthesis;
  • creation of conditions for adequate metabolism;
  • excretion of metabolic products.

The yolk sac performs all its functions until the main internal organs form in the body of the fetus and take over this work. After 12 weeks, the yolk sac is no longer needed. By the beginning of the second trimester, only a small cystic formation at the base of the umbilical cord remains from the yolk sac.

Yolk sac on ultrasound

In an ultrasound examination with a transvaginal probe, the yolk sac is determined from the 6th to the 12th week of pregnancy. Minor deviations (up to 2 weeks) in any direction are allowed. The absence of a yolk sac on ultrasound is an unfavorable sign, indicating serious violations during pregnancy.

During an ultrasound, the doctor evaluates the location, shape and size of the yolk sac. The size of the yolk sac will depend on the gestational age.

Yolk sac norms by week:

It is important to remember that the size of the yolk sac changes rapidly in early pregnancy. Minor deviations should not frighten a pregnant woman and cannot be the basis for making serious diagnoses. If the size of the yolk sac does not correspond to the norm, the doctor must carefully examine the embryo, determine the location of the fetal egg and other parameters. If necessary, a second ultrasound is performed after 1-2 weeks.

Timing for an ultrasound:

  • 6-7 weeks;
  • 12-14 weeks.

At a period of 6-7 weeks, the first ultrasound examination during pregnancy is performed. During the procedure, the doctor confirms the fact of pregnancy and determines its duration. The doctor indicates the location of the fetal egg (in the uterus or outside it), assesses the condition and localization of the yolk sac and chorion. The size of the fetus, their correspondence to the gestational age and the size of the yolk sac are determined. At 6 weeks, the heartbeat of the embryo is also heard and its viability is assessed.

At a period of 12-14 weeks, the first ultrasound screening is performed. During the procedure, the doctor assesses the condition of the embryo, chorion and yolk sac. During this period, the yolk sac reaches its maximum size. When ultrasound is performed at a later date, the yolk sac begins to dissolve and is not always visualized on the screen. After 14 weeks, the yolk sac is not normally detected.

Adverse symptoms:

  • absence of the yolk sac for up to 12 weeks;
  • thickening of the yolk sac more than 7 mm or a decrease of less than 2 mm;
  • change in the shape of the yolk sac.

In combination with other symptoms, these conditions may indicate a high risk of abortion in the first trimester. To clarify the diagnosis, an additional examination on an expert class apparatus may be required.

Pathology of the yolk sac

When conducting an ultrasound, the doctor can identify such conditions:

The yolk sac is not visualized

Normally, the yolk sac is determined by ultrasound in the period from 6 to 12 weeks. The absence of a yolk sac is an unfavorable sign. If for some reason such an important organ dissolves ahead of time, the embryo ceases to receive the substances necessary for its development. The synthesis of hormones and enzymes is disrupted, the production of red blood cells stops. With premature reduction of the yolk sac (up to 12 weeks), spontaneous miscarriage occurs. It is not possible to save pregnancy with medications.

The absence of a yolk sac on ultrasound (from 6 to 12 weeks) is considered one of the signs of a regressing pregnancy. The heartbeat of the embryo is not determined, its size does not correspond to the gestational age. Treatment is surgical only. With a regressing pregnancy, the fetal egg is removed and the uterine cavity is scraped.

Yolk sac less than normal

Possible options:

  • The yolk sac is defined as a rudimentary formation.
  • The size of the yolk sac does not correspond to the gestational age (less than normal).

Any of these situations suggests that premature resorption of the yolk sac has begun. If at the time of the reduction of the sac the internal organs of the fetus are not yet formed and are not able to fully function, the death of the embryo and spontaneous miscarriage occur. In some cases, uterine contraction and miscarriage do not occur after the death of the embryo. This condition is called regressive pregnancy.

Yolk sac is larger than normal

The main reason for this symptom is the incorrect determination of the gestational age. This is possible with an irregular menstrual cycle (against the background of various gynecological pathologies or in nursing mothers). In this situation, the doctor should estimate the size of the embryo and recalculate the gestational age, taking into account the available data.

An important point: a change in the size, shape or density of the yolk sac is important only in combination with other ultrasonic indicators. If any abnormalities are detected, the condition of the embryo (localization, size, heartbeat) should be assessed. If the baby grows and develops according to the gestational age, there is no cause for concern. Changes in the yolk sac in this case are considered an individual feature that does not affect the course of the first trimester.

It is so established by mother nature that each organ performs its assigned function in the body. Gradually, with the development of science, mankind has studied each organ and its significance in our body. Only with the advent of ultrasound equipment did doctors have the opportunity to look into the secret world of the origin of life, but this only added new questions that need answers. One of these mysteries was, at that time, an unknown organ, the yolk sac.

By order of the Ministry of Health of the Russian Federation, all pregnant women registered in antenatal clinics at the place of residence are required to undergo three ultrasound screenings at different gestational ages:

  1. 10-14 weeks;
  2. 20-24 weeks;
  3. 30-34 weeks.

The first ultrasound examination is performed from 10 to 14 weeks. But for more accurate data, it is better to do an ultrasound at the end of the first trimester. During this period, it is easier to detect deviations in the development of the embryo, and in case of serious defects, it is safer for the woman's health to get rid of the abnormally developing fetus.

Ultrasound, which is performed before the first screening, is carried out only to establish pregnancy. And they are not able to identify any pathologies or abnormalities, because in the short term the size of the fetal egg cannot allow this.

But the doctor may prescribe an ultrasound examination, if necessary, more than three times.

Inspection by the device using ultrasonic waves is carried out in two ways: through the abdominal wall or through the vagina.

Ultrasound in the first trimester is evaluated according to the following indicators:

  1. Coccyx-parietal size. This is the size of the embryo from crown to tailbone. Each doctor has a table of the ratio of the length of the embryo and gestation. KTR completely depends on the term.
  2. Heart rate. This criterion allows to identify congenital pathologies of the cardiovascular system. The doctor also has a table of normative indications by which early hypoxia and heart defects can be determined.
  3. The thickness of the collar space. This is the length of the area between the skin of the embryo and the soft tissues of the cervical vertebrae. The indicator helps to identify terrible diseases such as Down syndrome. The collar space disappears after 14 weeks after conception.
  4. The position of the chorion. Doctors call chorion in the first trimester the placenta. This standard indicates in which part of the uterus the fetus has taken its place.
  5. The size of the nose bone. Like other criteria, the length of the nasal bone on screening will help to identify a violation in the development of the baby. If ossification of the bridge of the nose is not detected or it is too small, then this indicates a chromosomal abnormality. If no other violations were found, then there is no reason to panic.
  6. Yolk sac. This indicator is of particular importance, as it helps to detect an undeveloped pregnancy. There is a thread between the yolk sac and the result of gestation.

In addition to studies on ultrasound equipment, biochemical screening is done in the period from 10 to 12 weeks. Blood sampling must be taken on the same day on which the ultrasound was performed. The analysis will reveal the likelihood of the birth of a child with chromosomal disorders.

What is a yolk sac?

The yolk sac, or gestational sac, is a circular vesicle attached to the abdominal cavity of the embryo. Inside the sac is a vital yolk, which plays a crucial role in the development of the fetal egg during placentation.

This organ is present in many mammals, birds, fish and cephalopods in the early stages of development and persists throughout life as a cyst-like process in the intestine with the remaining yolk.

Main functions of the yolk sac

Without this small bubble, the full development of the fetal egg is impossible. It takes on many functions, including the nutrition and respiration of the embryo, while the organs corresponding to this are absent.

In addition to nutrition and respiration, the membrane shell with yolk performs the duty of the primary circulatory system, through which oxygen and nutrients are transferred to the embryo.

Yolk sac during pregnancy

The gestational sac is proof of a healthy uterine pregnancy. With ectopic gestation, this membrane sheath is not visualized. The "pouch" appears in the second week of embryonic development and protects the fetus almost until the end of the first trimester, until other organs begin their work.

Between the fifth and sixth weeks, the pouch should be clearly visible on ultrasound. This is one of the important criteria for the proper development of the embryo. The average diameter of the membrane shell is 5 mm.

Between the seventh and tenth weeks, the size of the bubble normally reaches up to 6 mm in diameter.

After 10 weeks, the yolk sac gradually ends its activity and must necessarily decrease in size. By the beginning of the second trimester, the fully formed placenta takes over the function of nutrition and respiration, and the yolk membrane enters the fetal cavity and only a small process in the umbilical cord region remains in its place.