When the yolk sac and embryo appear. Yolk sac during pregnancy: normal, size by week

The embryo and the membranes surrounding it are the main initial components of the amniotic egg. As the fetus develops, the space around it also increases - this is a normal process of embryo development. Next, you are invited to familiarize yourself with key information directly about the fertilized egg, as well as regarding the peculiarities of changes in its size during pregnancy and possible pathologies of formation.

As you know, fertilization occurs through the penetration of a male sperm into a female egg. After this, the active process of embryo development begins: first, the fertilized egg is divided into 2 parts, then into 4, then into 8, etc. As the number of cells increases, the embryo itself grows. Without stopping to develop, the embryo moves towards its destination, which is normally the cavity of the female uterus. It is the mentioned group of cells that represents the fertilized egg in question.

Once the desired location is reached, the embryo is implanted into the wall of the uterus. On average, this process takes up to 7-10 days after the sperm penetrates the egg. Until reaching its destination, nutrition of the fertilized egg is provided directly by the egg, and after consolidation, by the uterine mucosa.

Over time, the functions of providing nutrition to the embryo are taken over by the placenta, which is formed from the outer layer of the fertilized egg. Directly on the mentioned outer layer there are so-called. villi, which ensure implantation of the embryo in a suitable place.

The formation and successful consolidation of the fertilized egg is the main sign of the normal course of female pregnancy. On average, the embryo becomes visible during ultrasound examination 5 weeks after the missed period, while the fertilized egg can usually be seen after 2 weeks. If during the first ultrasound the doctor sees the so-called. empty ovum, after a couple of weeks the test is repeated.

Normally, the embryo is visualized by the 6-7th week of pregnancy. During the same period, his heartbeat is usually noticeable. If there is no embryo in the ovum during repeated ultrasound examination, a non-developing pregnancy is diagnosed.

In view of this, if menstruation is delayed, a woman should have an ultrasound scan as early as possible in order to promptly detect existing abnormalities and, if such a possibility is present, undergo treatment to eliminate the identified problems.

When assessing the condition of the ovum, the specialist first of all pays attention to its shape and internal diameter. During the first weeks, the shape of the fertilized egg is close to oval. By assessing the internal diameter, the doctor can draw conclusions about the expected gestational age. Along with this, not every woman’s fertilized egg has the same size, so when determining the gestational age, an error often occurs, averaging one and a half weeks. For more accurate results, fetal CTE and other diagnostic measures are assessed.

Features of the growth of the fertilized egg

As noted, the size of the fertilized egg, in the absence of various kinds of pathologies, is constantly increasing.

More detailed weekly information regarding the normal size of the gestational sac is given in the following table.

Table. Sizes of fertilized egg by week

Possible developmental disorders of the ovum

Under the influence of certain factors, the development of the fertilized egg can occur with certain pathologies. You can find a description of the most commonly diagnosed anomalies in the following table.

Table. Pathologies of development of the ovum

Pathologies	Description
Form violations	The shape of the fertilized egg in both scans up to 5-6 weeks is usually round. By 6-7 weeks, the fetal egg becomes oval in a longitudinal scan, but remains round in a transverse scan. Along with this, the development of form can occur with various kinds of deviations. Most often, this is caused by various types of tumors in the uterine cavity. Also, this pathology can occur in the case of partial placental abruption.
Pathologies of location	In the absence of deviations, implantation of the fertilized egg most often occurs in the fundus of the uterus or its posterior wall, sometimes in the area of ​​the internal os or at the top of the uterus. Other options for the location of the ovum are assessed by a specialist. He also makes a decision on further actions in relation to a particular patient.
Dimensional violations	Information regarding changes in the size of the ovum as pregnancy progresses has been provided previously. Significant deviations from the given values ​​in both directions are considered pathological, and conclusions about their significance are made by a specialist.
Functional pathologies

It is impossible to give any definite answer regarding the causes of the development and treatment of pathologies in the development of the ovum - each case requires individual consideration by a qualified specialist. Only a doctor can objectively assess the situation and make the most appropriate decision.

Regularly undergo the necessary examinations, follow the recommendations of your treating specialist and be healthy!

Video - Size of fertilized egg by week of pregnancy table

It is so established by Mother Nature that each organ performs its assigned function in the body. Gradually, with the development of science, humanity has studied every 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 needed answers. One of these mysteries was the then unknown organ, the yolk sac.

By order of the Ministry of Health of the Russian Federation, all pregnant women registered with antenatal clinics at their place of residence are required to undergo ultrasound screening three times at different stages of gestation:

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

The first ultrasound examination is carried out 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 abnormalities in the development of the embryo, and in the case of serious defects, it is safer for the woman’s health to get rid of the abnormally developing fetus.

An ultrasound scan, which is performed before the first screening, is carried out only to establish pregnancy. And we are unable to detect any pathologies or abnormalities, because in a short period of time the size of the fertilized egg cannot allow this.

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

Examination with a device using ultrasonic waves is carried out in two ways: through the abdominal wall or through the vagina.

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

1. Coccyx-parietal size. This is the size of the embryo from the crown to the tailbone. Every doctor has a table of the relationship between embryonic length and gestational age. KTE depends entirely on the period.
2. Heart rate. This criterion allows us to identify congenital pathologies of the cardiovascular system. The doctor also has a table of normative indications that can be used to determine early hypoxia and heart defects.
3. 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 nuchal translucency disappears after 14 weeks of conception.
4. Position of the chorion. Doctors call the placenta in the first trimester chorion. This standard indicates in which part of the uterus the fetus has taken its place.
5. Nose bone size. Like other criteria, the length of the nasal bone during screening will help identify abnormalities 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 are 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 certain thread between the yolk sac and the result of gestation.

In addition to studies using 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 having a child with chromosomal abnormalities.

What is a yolk sac?

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

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

Main functions of the yolk sac

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

In addition to nutrition and respiration, the membrane membrane with the yolk serves as the primary circulatory system, through which oxygen and nutrients are transferred to the embryo.

Yolk sac during pregnancy

The gestational sac is evidence of a healthy intrauterine pregnancy. During ectopic gestation, this membranous membrane is not visualized. The “bag” 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 sac 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 breathing, and the yolk membrane is absorbed into the fetal cavity and in its place only a small appendage remains in the umbilical cord area.

Yolk sac norms by week

The gestational sac appears in the second week after conception; it is visible on the ultrasound monitor only in the fifth and sixth weeks. During the research, doctors determined the norms for the diameter of the yolk sac based on the timing of embryo development. These norms are considered signs of a favorable pregnancy:

1. In the fifth week – 3 mm.
2. At the sixth week – 3 mm.
3. In the seventh week – 4 mm.
4. At the eighth week - 4.5 mm.
5. At the ninth week – 5 mm.
6. At the tenth week - 5.1 mm.
7. At the eleventh week - 5.5 mm.
8. At the twelfth week - 6 mm.
9. At the thirteenth week - 5.8 mm.

After 10-12 weeks, the gestational sac begins to decrease in size.

What does not visualizing the yolk sac indicate?

Modern equipment makes it possible to detect and reduce the risk of complications during pregnancy at any stage. If, during the examination, the yolk “vesicle” is not visualized during the period between six and ten weeks, this indicates an unfavorable course of pregnancy. Because this organ can accurately assess the state of development of the embryo.

The absence of a gestational sac is a sign of a missed or undeveloped pregnancy. In case of a frozen pregnancy, urgent cleaning of the uterine cavity is necessary, but it is necessary to first conduct repeated studies after 7 days to ensure the accuracy of the diagnosis.

An undeveloped gestational sac in the fertilized egg often indicates a lack of the hormone progesterone. Timely treatment with drugs containing progesterone allows you to save the fetus and avoid subsequent complications.

What do increases and decreases mean?

Small deviations from the norm in the size of the yolk sac are not an indicator of any pathology or threat to the fetus.

A belated decrease towards the end of the first trimester indicates the slow resorption of an already unnecessary organ. Additional examination is necessary after 7 days to ensure that there are no abnormalities in fetal development. If there are no pathologies and all other indicators are normal, then there is no reason to worry either. If any abnormalities are detected, cleaning the uterine cavity is recommended. The shorter the period, the safer it is for the mother’s health.

An increase in the size of the yolk sac above normal also does not immediately indicate an existing pathology. Diagnostics are required to determine possible causes. Taking certain medications, poor diet and stress can cause an increase in the diameter of the yolk sac. Or simply an individual feature that does not portend any threat to the fetus. The doctor must perform a repeat ultrasound to clarify and confirm the diagnosis.

An increase, decrease, irregular shape or compaction of the shell with nutritious yolk from the established standards is significant only in conjunction with violations of other indicators.

Is your yolk sac the right size for your due date?

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When conducting the very first ultrasound examination, which is done when menstruation is delayed and in order to accurately diagnose the presence of intrauterine pregnancy, the fertilized egg can be examined. It is when the doctor sees this miniature formation on the monitor that he already informs the woman that she will soon become a mother. On the monitor you can see the fertilized egg, which is a small oval-shaped formation. In the early stages, the embryo, which will subsequently develop and grow in the fertilized egg, is not yet visualized, but soon it will grow up, and then it will be possible to clearly see it.

An empty fertilized sac is an egg without an embryo when pregnancy does not develop. The embryo is often visible already from the fifth week of pregnancy, but sometimes there are cases when even at this stage the doctor does not see the embryo during an ultrasound examination, in such a situation a repeat ultrasound is prescribed. Very often, a repeat ultrasound shows both the embryo and its heartbeat. When the embryo is not visible after six to seven weeks, then, unfortunately, there is a high risk that the pregnancy will not develop. In this article we will look at the norms of the fertilized egg by week.

What is a fertilized egg

The fertilized egg consists of embryonic membranes and an embryo. This period of pregnancy is its first stage of development. And it all starts with the fusion of two cells – male and female.

Then the fertilized egg actively begins to divide, first into two parts, then into four, and so on. The number of cells, like the size of the fetus, is constantly growing. And the entire group of cells that continue the division process moves along the fallopian tube to the zone of its implantation. This group of cells is the fertilized egg.

Having reached its goal, the fertilized egg attaches to one of the walls of the woman’s uterus. This occurs a week after fertilization. Until this time, the fertilized egg receives nutrients from the egg itself.

• Fertilized egg 2 weeks after insertion into the uterine cavity, it nourishes the swollen mucous membrane of this reproductive organ, which is already prepared for the process of development and nutrition of the fetus until the time of formation of the placenta.
• The baby's place, or placenta, is created from the outer shell ovum at 3 weeks, which at this time is already densely covered with villi. These villi at the site of attachment of the fertilized egg destroy a small area of ​​the uterine mucosa, as well as the vascular walls. Then they fill it with blood and immerse it in the prepared area.
• In general, the fertilized egg is the very first sign of a normally ongoing pregnancy. It can be examined by ultrasound after two weeks of missed menstruation. Usually in this case it is visible fertilized egg 3-4 weeks. The embryo becomes noticeable only at the 5th week of pregnancy. However, if the doctor diagnoses the absence of an embryo in fertilized egg 5 weeks- in other words, an empty fertilized egg, then the ultrasound is repeated again after a couple of weeks.
• Usually in such a situation, at 6-7 weeks the fetus and its heartbeat begin to be visualized. When fertilized egg at 7 weeks is still empty, this indicates a non-developing pregnancy. In addition to this complication, others may appear in the early stages of pregnancy - incorrect location of the fertilized egg, its irregular shape, detachments, and others.
• It is for this reason that it is important to undergo an ultrasound examination as early as possible, so that the situation can be changed if it can be corrected. Since in the first trimester ( fertilized egg up to 10 weeks) there is a high probability of spontaneous miscarriage, detachment and other pathologies. However, enough about the sad things.

Fertilized egg at 6 weeks and until this stage of pregnancy it has an oval shape. And an ultrasound examination usually evaluates its internal diameter - the SVD of the fetal egg. Because ovum size 7 weeks or at another stage of pregnancy is a variable value, that is, the error in identifying the gestational age using this fetometric indicator.

On average, this error is 10 days. Gestational age is usually determined not only by this indicator, but also by the values ​​of the coccygeal-parietal size of the fetus and other indicators, which are also very important

Diameter of fertilized egg by week

When the fertilized egg has a diameter of 4 millimeters, this indicates a fairly short period of time - up to six weeks.

• Often they are fertilized egg size 4 weeks. Already at five weeks, the SVD reaches 6 millimeters, and at five weeks and three days the fertilized egg has a diameter of 7 millimeters.
• At the sixth week, the gestational sac usually grows to eleven to eighteen millimeters, and the average internal size of the gestational sac of sixteen millimeters corresponds to a period of six weeks and five days. At the seventh week of pregnancy, the diameter ranges from nineteen to twenty-six millimeters.
• Fertilized egg at 8 weeks increases to twenty-seven to thirty-four millimeters. At this stage, the ultrasound can clearly examine the fetus.
• Fertilized egg 9 weeks grows to thirty-five to forty-three millimeters.
• And at the end of the tenth week, the fertilized egg measures about fifty millimeters in diameter.

As you can see, fertilized egg at 4 weeks It differs very much in size during the tenth week.

The question of how quickly the fertilized egg grows can be answered with confidence: until the fifteenth to sixteenth week, its size increases by one millimeter every day. Further, the diameter of the fertilized egg increases by two to three millimeters per day.

Average size of the fertilized egg in the first trimester of pregnancy

Date of last menstruation (weeks)	Time at conception (weeks)	Inner diameter (mm)	Area (mm 2)	Volume (mm 3)
5	3	18	245	2187
6	4	22	363	3993
7	5	24	432	6912
8	6	30	675	13490
9	7	33	972	16380
10	8	39	1210	31870
11	9	47	1728	55290
12	10	56	2350	87808
13	11	65	3072	131070

A special organ that forms in the initial stages of pregnancy and eventually atrophies until the end of the third trimester is called the yolk sac. It resembles the shape of a ring and has thin walls. The size of the yolk sac from the fifth to the twelfth week should be 3-6 millimeters in diameter.

Yolk sac during pregnancy

This small organ plays a very important role in the development of the embryo:

• Its name suggests that it contains nutrients, which in turn are used in the initial stages of embryo development.
• During a pregnancy of three weeks, germ cells begin to form in the yolk sac, which then enter the rudimentary gonads of the embryo.
• The yolk sac is capable of producing the very first red blood cells, namely red blood cells, which are responsible for respiratory function.
• It is the yolk sac that is responsible for the transformation of substances that will then flow into the fetal liver.

Even these brief enumerations lead us to the idea that the role of the yolk sac is very important. It is very important to conduct an ultrasound examination in the early stages of pregnancy, with its help the doctor will be able to assess the condition of this formation.

Pathologies of the yolk sac

When examining the yolk sac, one may encounter the following phenomena: increased density of the yolk sac, its doubling or pathological change in shape, pathological size, and even the absence of this formation.

But the assessment of such pathological signs as a decrease or increase in the yolk sac is very subjective; it very much depends on the quality of the device and the qualifications of the doctor. Therefore, in such situations, you are usually advised to undergo repeated diagnostics in special centers, where the level of equipment and doctors is quite high.

If the yolk sac is not able to function normally, that is, it freezes, then spontaneous abortion, if the abortion does not occur, then there is a high probability of fetal pathology.

Undoubtedly the first Ultrasound For any woman, this is a very exciting stage during pregnancy. Right now she is beginning to worry about the health of her unborn child, his normal development. Naturally, if during the examination the doctor discovers some abnormalities, including the yolk sac, then the mother begins to worry. You should not draw premature conclusions; it would be better to calm down and discuss the possible consequences with your doctor. There are situations when neither the embryo nor the yolk sac are visible during an ultrasound. But the fertilized egg is still there. Unfortunately, this situation is a sign of a failed pregnancy. But there are also cases when the size of the yolk sac is much larger than usual. This is not a pathology, but it is imperative to monitor the progress of the situation.

The yolk sac is not visualized:

For example, ladies cite the results of an ultrasound, in which, for example, neither the embryo nor the yolk sac are visualized (that is, not visible). At the same time, the fertilized egg is present. Unfortunately, this situation is called “anembryony” - that is, the pregnancy did not take place.

The yolk sac is enlarged:

In other cases, on the contrary, it means that the yolk sac is larger than normal. The online consultant reassured the woman who came with a similar problem, explaining that this does not indicate any specific pathology and may be an individual feature. But, of course, it is necessary to control the development of the situation.

In general, every expectant mother should imagine what processes take place in her body at one or another stage of pregnancy or menstrual cycle. You should know how some medications, stress, and foods can affect the state of the reproductive system and fetus. Treat pathologies that may complicate pregnancy in a timely manner. But the most important thing is to find a specialist who will actually, and not formally, take responsibility for your health, bearing a child and a successful birth.

The fertilized sac is a round or ovoid (egg-shaped) formation that surrounds the embryo, usually located in the upper half of the uterine cavity.

In the early stages of pregnancy (in the first trimester), an ultrasound examination is performed to determine the localization (location) of the fetal egg. On an ultrasound, the fertilized egg looks like a small dark gray (almost black) spot with clear contours.

The presence of a fertilized egg in the uterine cavity eliminates the possibility of ectopic pregnancy. In a multiple pregnancy, you can see two separately located fertilized eggs.

At what stage of pregnancy can you see the fertilized egg?

Approximately two and a half weeks after conception, if menstruation is delayed by 3-5 days or more, that is, in the fourth to fifth obstetric week of pregnancy from the last day of the last menstruation, an ultrasound diagnostician can already see the fertilized egg in the uterine cavity using transvaginal ultrasound. The diagnostic level of hCG in the blood serum, at which the fertilized egg should be visible in the uterine cavity during transvaginal ultrasound, is from 1000 to 2000 IU.

The fertilized egg looks like a rounded black (anechoic or echo-negative, that is, not reflecting ultrasonic waves) formation, the diameter of which is very small and ranges from 2-3 mm. The embryo and extra-embryonic organs still have a microscopic structure and therefore are not yet visible using ultrasound. Using a parameter like average internal diameter of the ovum It is most advisable in the first 3-5 weeks of pregnancy from conception, when the embryo is not yet visible or is difficult to detect. The error when using the measurement usually does not exceed 6 days.

Size of fertilized egg by week of pregnancy

The size of the ovum by week is a very important indicator during pregnancy. For example, a gestational sac diameter of 3 mm corresponds to a gestational age of 4 weeks, and a gestational sac diameter of 6 mm corresponds to a gestational age of 5 weeks. An increase in the average diameter of the ovum occurs in the early stages of pregnancy at a rate of approximately 1 millimeter per day.

Most standard indicators for the average internal diameter of the ovum are limited to a period of 8-10 weeks. This is due to the fact that after 6–7 weeks of pregnancy, the size of the fertilized egg cannot reflect the growth of the embryo. With its advent, the coccygeal-parietal size of the embryo (CTE) is used to estimate the gestational age.

The dimensions of the average internal diameter of the ovum by week are given in the calculator.

Irregularly shaped ovum (deformed ovum)

If the fertilized egg is located in the uterine cavity, then such a pregnancy is called a physiological uterine pregnancy. A fertilized egg up to 5-6 weeks normally on ultrasound has a round or drop-shaped shape, surrounded by a thin membrane. By 6-7 weeks, it completely fills the uterine cavity and acquires an oval shape in a longitudinal scan, and a round shape in a transverse scan. If on an ultrasound the doctor sees a deformation of the fertilized egg (it is elongated, flattened on the sides, looks like a bean), then this may indicate uterine tone. A change in the shape of the fertilized egg is also possible with partial detachment. Significant deformation with unclear contours is observed during frozen pregnancy.

Timely diagnosis of deformation of the ovum during pregnancy makes it possible to save the child.

Empty fertilized egg

Normally, the fertilized egg in the uterine cavity is visible on transvaginal ultrasound approximately 32-36 days after the first day of the last menstrual period. An important place is given yolk sac, which is of great importance in the development of the fertilized egg. During the physiological course of pregnancy, the yolk sac has a round shape, liquid contents, and reaches its maximum size by 7–8 weeks of pregnancy.

The embryo appears as a thickening along the edge of the yolk sac. The image of a normal embryo with a yolk sac looks like a "double bleb". By seven weeks, the yolk sac measures 4-5 mm. A relationship has been established between the size of the yolk sac and pregnancy outcome. When the diameter of the yolk sac is less than 2 mm and more than 5.6 mm, spontaneous miscarriage or non-developing pregnancy is quite often observed at 5–10 weeks.

The absence of a yolk sac with an average internal diameter of the ovum of at least 10 mm is an unfavorable ultrasound criterion for the threat of miscarriage.

An empty (false) ovum is an accumulation of fluid, usually irregular in shape, located near the border of the endometrium.

Sometimes there are cases when the fertilized egg has the usual shape and size, but there is no yolk sac or embryo inside it. The chorion of an empty fertilized egg produces the hCG hormone, as in normal physiological pregnancy, so pregnancy tests will be positive. An ultrasound performed in the early stages of pregnancy can be erroneous, since the earlier it is done, the less chance there is of seeing the embryo. Before 7 weeks of pregnancy, a repeat study is required to clarify the diagnosis.

When on an ultrasound they see a fertilized egg in the uterine cavity, but do not see the embryo itself, doctors call this pathology anembryony (without embryo).

The following signs indicate a non-developing pregnancy (death of the embryo): altered membranes, the absence of an embryo when the size of the fetal egg is more than 16 mm in diameter, or the absence of a yolk sac when the membranes are more than 8 mm in diameter (when performing a transabdominal ultrasound: 25 mm - without an embryo and 20 mm – without yolk sac); uneven contours, low location or absence of the double decidual sac.

In the early stages, the cause of pregnancy loss is most often chromosomal abnormalities that arose during the process of fertilization.