This is how our consciousness works: for thousands of years, women have been carrying their children without thinking at all about some trifles, for example, about what stages of development the fetus goes through - the most important thing is that children are born viable and healthy. However, science has come a long way since then. Fetal ultrasound is now done to every pregnant woman, and more than once. And just in the results of this examination, many discover that the fetus has some kind of yolk sac (a sac, as many affectionately call it). And, of course, it becomes interesting where he came from, why he is needed and where he is in an adult.

The yolk sac is formed at the beginning of the third week from the endoblastic vesicle (a derivative of the endoblast). It functions for a short time - about three months, but is of great importance for the development of the fetus. 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 developing embryo.

Why do you need a yolk sac?

At the earliest stages of development, when the embryo is just being formed, the yolk sac performs a variety of functions, without which normal development is impossible.

FROM 18 -th days the beginning of a new life in the wall of the yolk sac, the first embryonic erythrocytes (erythroblasts) are formed and capillaries begin to grow, from which the entire circulatory system of the fetus is later formed.

FROM 28 -th days the walls of the yolk sac produce the first germ cells, which a little later will move to the anlage of the gonads of the embryo. It is important to note that at this time the eggs of the future girl are laid. If at this stage the mother has been ill or experienced severe stress, egg laying will not happen correctly and in the future an adult woman will suffer from infertility.

Before sixth weeks the yolk sac plays a role primary liver” and produces proteins that are very important for the development of the embryo, such as alpha-fetoprotein.

The yolk sac also takes an active part in metabolic processes, the formation of immunity and collects fetal secretions.

Where does the yolk sac go?

At the end of the first trimester, the fetus is fully formed and passes to the placental type of blood circulation. The yolk sac becomes unnecessary and is reduced, that is, disappears. Until the end of pregnancy, it remains in the form of a small cyst at the base of the umbilical cord. If the yolk sac is reduced before the due date, when all the organs of the fetus have not yet had time to form, then the pregnancy will stop developing. It’s just that the embryo will not be able to move to a new stage of development and become a fetus. This is what most often causes the development of missed pregnancy and spontaneous abortions.

What about an ultrasound?

On ultrasound, the yolk sac is visible from the 6th to the 12th week from conception. If the doctor does not see the yolk sac, this is a very unfavorable sign: pregnancy can stop developing at any time. Also unfavorable is the premature disappearance of the yolk sac.

Normally, the yolk sac should have dimensions:
less than 5.5 mm for a period of 5–10 weeks;
more than 2 mm for a period of 8-12 weeks.

What does the yolk sac not visible mean?

The yolk sac is formed on the 15-16th day after conception and ceases to function at the end of the first trimester - 11 weeks of pregnancy. The yolk sac plays an important role in the respiration and nutrition of the embryo, performs excretory and other functions before this function is taken over by the formed organs of the fetus and the placenta. After 12-13 weeks, the yolk sac is drawn into the fetal cavity, shrinks and remains only in the form of a cystic formation near the base of the umbilical cord. Yolk bag in norm rendered from 6 before 12 weeks pregnancy and is a rounded thin-walled anechoic formation in the immediate vicinity of the embryo. Its diameter is 4-8 mm (on the 7th week from 4-5 mm), gradually increases to 10 mm, and then its reverse development begins.

If the yolk sac is not visualized between 6 and 11 weeks:- You may have incorrectly set the gestational age, and the pregnancy is less than 6 weeks (up to 6 weeks, the yolk sac is normally not visualized). At the same time, ultrasound can already determine the heartbeat of the embryo (from 4-5 weeks) and the embryo is visible. - The absence of a yolk sac after 6 weeks may indicate an unfavorable course of pregnancy, which may end in an interruption or a frozen pregnancy. The prognosis is unfavorable. It is necessary to undergo an ultrasound examination again, preferably by a transvaginal method with a high-resolution apparatus, to verify the presence or absence of a yolk sac. - After 12 weeks is normal if the yolk sac is not detected. This means that the fetus began to receive nutrients through the placenta.

Yolk sac

YOLK SAC- in embryology, an outgrowth of the middle section of the intestine in the embryos of cephalopods, most vertebrates and humans. Filled with yolk and performs the function of nutrition, respiration and hematopoiesis ... Big Encyclopedic Dictionary

In terms of 5-6 weeks, the largest diameter of the fetal egg is 1-2 cm. At 8 weeks, the fetal egg occupies half of the uterus: at 9 weeks it occupies 2/3 of the uterus, at 10 weeks - the entire uterus.

The gestational age with an accuracy of 1 week is determined by the average diameter of the fetal egg. On a longitudinal section, measure the maximum size along the length (length), at an angle of 90 ° - the anteroposterior size (AP). Make a transverse cut at a right angle to the longitudinal plane and measure the largest dimension of the width of the fetal egg. The average diameter of the fetal egg is determined as the arithmetic mean of three sizes.

Average diameter of the fetal egg = Length + Anteroposterior size + Width / 3

With transvaginal echography one of the first signs of uterine pregnancy is an anechoic rounded inclusion with a diameter of only a few millimeters, located in the uterine cavity against the background of a thickened hyperechoic endometrium. A fetal egg can be detected no earlier than 4 weeks and 3 days, but is most often detected during transvaginal examination after 5 weeks.

Yolk sac

Although mammals and there is in essence no accumulated yolk in the egg, the yolk sac is formed in the early stages of development as if there were actually a yolk. This retention of structure despite the loss of its original function is not uncommon and has led to the biological aphorism "morphology is more conservative than physiology".

Until the 6th week of pregnancy, the yolk sac for a child plays the role of a primary liver and produces vital proteins: transferrins, alpha-fetoprotein, alpha2-microglobulin. From the 18-19th day of pregnancy in the walls of the yolk sac, with the help of nuclear erythrocytes, the primary circulatory system is formed - a capillary network that will nourish the fetus. From 28-29 days, the yolk sac is responsible for the production of primary germ cells, which then migrate to the embryo and contribute to the formation of an embryo of a certain sex.

The yolk sac has various functions that determine the viability of the fetus. It fully fulfills its role as a primary nutrient by the end of the 1st trimester, until the formation of the spleen, liver and reticuloendothelial system in the fetus (the system subsequently responsible for the development of macrophages - part of the immune system). The yolk sac after 12-13 weeks of pregnancy ceases its functions, is drawn into the cavity of the embryo, contracts and remains in the form of a cystic formation - the yolk stalk, near the base of the umbilical cord. With the pathological development of the yolk sac, the pregnancy may be non-developing, or a miscarriage will occur.

Why is the size of the yolk sac so important during pregnancy?

At the first ultrasound examination, when it comes to actually confirming pregnancy, doctors always pay attention to the shape and size of the yolk sac. After all, these indicators are key in determining the problems that may arise with the development of the fetus. The thing is that the lack of yolk in such a bag can cause the pregnancy to freeze at a certain stage, and the fetus stops developing. Such a situation is quite dangerous not only for the unborn baby, but also for the woman herself, whose life may be endangered. The irregular shape of the yolk sac, in turn, can also indicate problems with the development of the fetus and the presence of various pathologies in its body, including genetic abnormalities.

Fetal egg 19*13*20 in it yolkbag 5 mm, corpus luteum 14 mm IR 0.45, the embryo is not visualized, period 5 weeks, monthly 6 days and 4 days (last month 10/23/15), tell me, is it worth worrying? Thanks! open

Good afternoon! Today I have 5 obstetric weeks of pregnancy, I did an ultrasound - 3 weeks and 1 day a fetal egg, size 9.5 mm, yolkbag 2 mm, the embryo is not visible. I constantly take hCG, at first it grew quickly, from 24.09 to 02.10 it ... open

Diagnosis of pregnancy complications by ultrasound results

The most common pathology in the first trimester is the threat of abortion. The main echo sign of the threat of interruption is a local thickening of the muscles of the uterus (myometrial hypertonicity). Several areas of hypertonicity can be determined. At the same time, the shape of the fetal egg changes: from round or oval, it becomes irregular, sometimes severely deformed. The most unfavorable situation is when the site of increased tone is located at the placenta formation site: in this case, detachment of the fetal egg and termination of pregnancy is possible.

In most cases, hypertonicity of the myometrium is accompanied by pain in the lower abdomen. This requires treatment aimed at maintaining pregnancy. In the event that the fetal egg loses contact with the uterine wall and exfoliates from its bed, a retrochorial hematoma is formed (a limited accumulation of blood between the fetal egg and the uterine wall). This is typical for a miscarriage that has begun. With a significant detachment, deformation and a decrease in the size of the fetal egg occur, and the death of the embryo. Clinically, bleeding of varying intensity is usually observed. The shortening of the cervix to 2.5 cm (the norm is 3.5-4 cm) and the funnel-shaped expansion of the internal pharynx also indicate the threat of termination of pregnancy.

If, against the background of bloody discharge from the genital tract, an ultrasound scan reveals an expansion of the uterine cavity and the presence of heterogeneous contents in it, and the fetal egg is not visible, then an incomplete miscarriage is diagnosed. In this case, hospitalization in the gynecology department is necessary to carry out curettage of the remnants of the fetal egg and stop bleeding.

A non-developing pregnancy is characterized by a smaller size of the fetal egg for a given gestational age, its deformation, fuzzy contours, a decrease in the thickness of the chorion, and the absence of heart contractions of the embryo.

The localization of the fetal egg in the cervical canal (cervical canal) is typical for cervical pregnancy. In this case, the best visualization is achieved with transvaginal ultrasound. In this situation, urgent hospitalization is necessary, since the likelihood of heavy bleeding is very high.

Quite often during pregnancy, a corpus luteum cyst occurs in one of their ovaries, which is a formation with a diameter of 3 to 8 cm with thick walls and a heterogeneous internal structure. This is a variant of the norm. A characteristic feature of this cyst is a gradual decrease in its size and disappearance by the end of the first trimester.

Cystic skidding is a rare complication observed in 1 case per 2000-3000 pregnancies associated with chorion pathology, in which the chorion turns into cluster-shaped formations that destroy all other structures of the fetal egg. In this case, the uterus is filled with many bubbles with fluid. With ultrasound, the uterus is visualized with dimensions larger than normal for a given gestational age, with an expanded cavity filled with inhomogeneous contents (the so-called “snowstorm” picture).

• less than 5.5 mm for a period of 5-10 weeks;
• more than 2 mm for a period of 8-12 weeks.

Many future mothers, getting into the ultrasound room, hear about the yolk sac during pregnancy. However, the ultrasound doctor does not always give complete answers to all questions of pregnant women.

What is the yolk sac during pregnancy - not to be confused with the corpus luteum

Even before conception, an egg cell is formed in one of the woman's ovaries, the names of which, having combined with the spermatozoon, will give a new life - the life of your child. In the middle of the menstrual cycle, the "pouch" or dominant follicle containing the mature egg, bursts

The egg is released and the egg travels to the uterus through the fallopian tubes. And in place of the bursting sac, a corpus luteum is formed, the purpose of which is the production of progesterone. This hormone is extremely important, it is designed to support and maintain a future pregnancy in the first trimester. Hormones produced by the yolk sac help prevent rejection of the fetus after attachment - implantation (i.e., reduce the risk of termination of pregnancy, spontaneous abortion), prepare the mammary glands for lactation, lower blood pressure and suppress the immune system, which ensures the loyalty of the mother's body to the new , actively developing life.

Yolk sac, what is it?

After conception, on the 15-16th day of pregnancy, the yolk sac is formed. Being the "temporary organ" of the baby, the yolk sac during pregnancy is an appendage located on the ventral side of the embryo. It contains a supply of yolk necessary for development. At first (before the functioning of the fetus's own organs), it performs the functions of the liver, spleen, and is also a supplier of primary germ cells, actively participating

tvuet in the formation of immunity and in metabolic processes.

The value of the size of the yolk sac

According to studies, an increase or, conversely, a decrease in the yolk sac, as well as an irregular shape, are often accompanied by a missed pregnancy. That is why it is so important to assess the size of the yolk sac during pregnancy.

first trimester ultrasound

With ultrasound in early pregnancy, it is the yolk sac that is an important diagnostic criterion. This is due to the fact that the size of the yolk sac in the first nine weeks of pregnancy significantly exceeds the size of the child. The yolk sac during pregnancy begins to be visualized from 5.5 weeks. With a normally developing pregnancy for a period of 5-10 weeks, the size of the yolk sac should be less than 5.5 millimeters. From 8 to 12 weeks of pregnancy

the size of the yolk sac should be more than 2 millimeters.

Reduction of the yolk sac

At the beginning of the fourth month of pregnancy, the fetus is already fully formed, and placental circulation begins, as a result of which the yolk sac, which has become unnecessary during pregnancy, disappears at a later date. However, there are cases when its reduction (decay) is delayed, and its cystic degeneration occurs. This fact should not cause much concern, provided that all other indicators of the screening ultrasound were normal. If anxiety does not leave you, you can do an ultrasound scan again - in about 2-3 weeks.

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 15th-16th day of embryo development (or on the 29th-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 matters 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.