Yolk sac sizes by week. What is a yolk sac during pregnancy

08.08.2019

A fertilized egg is a round or ovoid (egg-like) 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), ultrasound is performed to establish the localization (location) of the ovum. On ultrasound, the ovum looks like a small dark gray (almost black) spot with clear contours.

The presence of the ovum in the uterus eliminates the possibility of an ectopic pregnancy. In multiple pregnancies, two separate ovules can be seen.

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

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

The ovum looks like a round-shaped black (anechoic or echo-negative, that is, does not reflect ultrasonic waves) formation, the diameter of which is very small and ranges from 2-3 mm. The embryo and extraembryonic organs are still microscopic and therefore not yet visible with ultrasound. Using a parameter like average inner diameter of the ovum most expedient in the first 3-5 weeks of pregnancy from conception, when the embryo is not yet visible or is difficult to identify. The measurement error is usually less than 6 days.

The size of the ovum by weeks of pregnancy

The size of the ovum by week is a very important indicator during pregnancy. For example, a fetal egg diameter of 3 mm corresponds to a gestation period of 4 weeks, and a 6 mm fetal egg diameter corresponds to a 5th week of gestation. The 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 of the normative indicators of the average inner 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 ovum cannot reflect the growth of the embryo. Since its appearance, the coccygeal-parietal size of the embryo (CTE) is used to estimate the duration of pregnancy.

The sizes of the average inner diameter of the ovum by week are given in the calculator.

Irregularly shaped fertilized egg (deformed fertilized egg)

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

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

Empty fetal egg

Normally, the ovum in the uterine cavity is visible with transvaginal ultrasound approximately 32-36 days after the first day of the last menstruation. An important place is given to yolk sac, which is of great importance in the development of the ovum. In the physiological course of pregnancy, the yolk sac has a rounded shape, liquid content, reaches its maximum size by 7–8 weeks of gestation.

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

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

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

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

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

Non-developing pregnancy (death of the embryo) is evidenced by the following signs: altered fetal membranes, the absence of an embryo when the size of the ovum is more than 16 mm in diameter or the absence of a yolk sac when the membranes are more than 8 mm (when carrying out transabdominal ultrasound: 25 mm - without an embryo and 20 mm - without yolk sac); uneven contours, low location or absence of a double decidual sac.

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

The development of the embryo during a woman's pregnancy proceeds according to a certain scenario. Monitoring with the help of ultrasound diagnostics of certain primary organs, as well as their condition, makes it possible to diagnose certain pathologies at an early stage of a woman's pregnancy. Some pathologies may require an abortion, it is better that this be done at a short stage of pregnancy. The condition of some of the primary organs of the fetus makes it possible to predict the course of pregnancy and the likelihood of spontaneous abortion in some cases, as well as to conduct appropriate therapy. It is these primary organs that include the yolk sac, which appears at an early stage of development of the ovum.

Yolk sac. What it is?

Evolution has gone through a complex process, before man appeared in his true likeness. A kind of mini-evolution can be observed during pregnancy. With the development of the human embryo, organs appear that are characteristic of less complex biological species, which implies a single evolution and only the subsequent complication of the biological species.

The yolk sac is an organ that appears in the human embryo and provides nutrition and respiration of the ovum. A similar provisional organ also appears in embryos, bony and cartilaginous fish, cephalopods, birds and all reptiles. The yolk sac develops at the earliest stage of embryonic development - on the 15-16th day of development of the ovum, by overgrowing the yolk of a fertilized egg with embryonic tissue - endoderm and visceral leaf of the lateral plates. In most animals, with the exception of some mammals, including humans, the yolk sac is preserved as an intestinal process with undissolved yolk.

Yolk sac during pregnancy

Until the 6th week of pregnancy, the yolk sac for the baby plays the role of the primary liver and produces vital proteins: transferrins, alpha-fetoprotein, alpha2-microglobulin. From 18-19 days of pregnancy, a primary circulatory system is formed in the walls of the yolk sac with the help of nuclear erythrocytes - a capillary network that will feed 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 vitality of the fetus. It fully fulfills its role of primary nutrient matter 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). After 12-13 weeks of gestation, the yolk sac 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, pregnancy may not develop, or a miscarriage will occur.

What does it mean if the yolk sac is not visualized

Observation of the yolk sac is usually done during artificial insemination to analyze the fertilization process, although assessment of the yolk sac is an effective way to diagnose early pregnancy. There are different options for the pathologies of the development of the embryo. By the size of the yolk sac, one can judge how the pregnancy develops, with an insufficient size of the yolk sac, we can talk about a frozen pregnancy, in which cleaning of the uterine cavity is recommended. It is important to do it on time. Although in this case, there are effective methods of hormone therapy.

In general, the yolk sac is visualized between 6 and 12 weeks of gestation. If during this period the yolk sac is not visualized, then there is a high probability of complications. Premature reduction (contraction) of the yolk sac will suggest an undeveloped pregnancy. The likelihood of complications during pregnancy increases sharply if the size of the yolk sac is more than 5.5 mm (with a norm of max 6 mm) at 5-10 weeks and less than 2 mm at 8-12 weeks. In the second case, the risk of missed pregnancy is very high.

What does an enlarged or reduced yolk sac mean?

There is no need to panic if deviations from the norm are found, which will determine the results at 12-13 weeks. There are cases of normal pregnancy with a large yolk sac, which is significantly higher than the norm. Everything is purely individual. In addition, you need to understand that the assessment of the yolk sac is a subjective factor that largely depends on the quality of the ultrasound machine and the qualifications of the ultrasound diagnostician. But with a subjectively enlarged yolk sac, a triple test is usually immediately prescribed to determine if there are reasons for concern. Additional diagnostics are also prescribed if the yolk sac slowly dissolves after 12-13 weeks. Even with slow resorption, pregnancy can proceed without complications, but to remove all questions about the nature of the course of pregnancy and early development of the fetus, you need to pass a triple test and assess the possibility of genetic abnormalities (!) In the child. In the presence of genetic abnormalities, it is recommended.

Pathologies with underdevelopment of the yolk sac are mainly associated with a lack of progesterone in a woman's body, usually a progesterone-containing hormonal drug is prescribed to support the normal course of pregnancy. With the timely appointment of progesterone-based therapy, pregnancy usually proceeds normally. If you have a shortened second phase of the cycle or estrogen-progesterone deficiency occurs during the menstrual cycle, you need to pay special attention to the nature of the development of early pregnancy and take all steps to avoid a frozen pregnancy, which will require cleaning.

A lack of progesterone can be in women with a shortened menstrual cycle of 21 days, with the second phase of the cycle less than 10 days, with a chaotic basal temperature schedule. The state of the hormonal background can be independently assessed before pregnancy by measuring the basal temperature. Estrogen-progesterone deficiency will cause a chaotic basal temperature measurement.

) ultrasound examination is carried out in order to establish the localization (location) of the ovum. A fertilized egg is a round or ovoid (egg-like) formation that surrounds the embryo, usually located in the upper half of the uterine cavity. On ultrasound, the ovum looks like a small dark gray (almost black) spot with clear contours.

The presence of the ovum in the uterus eliminates the possibility of an ectopic pregnancy. In multiple pregnancies, two separate ovules can be seen.

How long can you see the fertilized egg.

Fertile egg: size by week

The sizes of the average inner diameter of the ovum by week are given in the calculator.

Irregularly shaped fertilized egg (deformed fertilized egg)

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

Empty fetal egg

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

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

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

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

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

What is SVD during pregnancy and how to determine it on ultrasound? There is only one answer to this question.

SVD is the average inner diameter of the ovum according to ultrasound diagnostics. This indicator is measured exclusively in millimeters.

Ovum illustration

The gestational age is characterized by certain values of the inner diameter. The digital value of the SVD is constantly changing, so the period is considered with an error from a week to one and a half. A more reliable sign is the CTE (coccygeal-parietal size). It should be noted that the coccygeal-parietal size of the embryo is less subject to individual fluctuations compared to the average inner diameter of the ovum, and therefore is used more often to establish a reliable gestation period. The error is approximately three days.

When the fetus is well visualized, the term is determined by the length of the fetus, and not by the indicator of the inner diameter. The coccygeal-parietal size is fixed during the planned ultrasound scan and reflects the actual size of the fetus in combination with the approximate weight of the fetus. As a rule, the measurement of CTE indicators is used before, and in later ultrasound studies, the biparietal diameter of the fetal head and abdomen is used.

Indicative indicators of SVD, depending on the timing of gestation

When the diameter of the ovum is approximately 4 millimeters, then the gestational age is. It is possible to assume that about four weeks have passed since the day of conception.
Closer to the fifth week, the diameter will reach 6 millimeters.
After a few days, the fetus becomes 7 millimeters.
the diameter increases to 12 - 18 millimeters.
The average SVD value for a period of six weeks and five days is 16 millimeters.

Fetal egg for ultrasound

Of course, the expectant mother is concerned about the following question: how intensively does the fetus grow in the second and third trimesters? We can say with confidence that its diameter grows by one millimeter daily. Then its value increases by an average of 2 - 2.5 millimeters every day. In the borderline period of 16 - 17 weeks, they stop measuring the inner diameter of the ovum, focusing on more reliable indicators.

Ultrasound examination at a short period of gestation

Diagnostics are carried out for the following purposes:

Diagnostics of the localization of the ovum

1. Establishing the exact localization of the fetus (in the uterine cavity or outside it). When the fetus is located outside the uterus, it is a question. When the fetus cannot be visualized or the recognition process is significantly hampered, then they resort to an accurate determination of the heartbeat of the embryo. Signs of fetal viability can be found in the fallopian tubes or abdomen.

In addition to this complication, other complications may appear at the initial stages of pregnancy: for example, an altered form of the ovum; incorrect attachment; high risk of placental abruption and other pathological disorders.

2. Determination of single or multiple pregnancy is not difficult. In the uterine cavity, there are two or more fetuses with active life.

3. Assessment of the main sizes of the ovum and embryo and their comparison with the indicators of the norm.

4. Study of the correct structure of the embryo and ovum to exclude serious congenital malformations. These can be chromosomal mutations (for example, Down's syndrome).

5. Assessment of vital signs is carried out on the basis of the presence of a heartbeat, which is detected already in the fifth week of gestation. The motor activity of the embryo is quite well determined after the seventh week of gestation.

At the initial stage, the movements are so weak and sporadic that they can hardly be distinguished during ultrasound. As the embryo grows, motor activity begins to resemble characteristic flexion and extension movements, and then active movements of the upper and lower extremities. Since individual moments of motor activity are rather short in time and are counted in seconds or their fractions, the definition of cardiac activity is used to register the fact of fetal activity.

6.. This small cystic formation provides the mother-to-be with important hormones to preserve the fetus in the early stages of development.

7. The study of the amnion and chorion is reduced to their ratio depending on the gestation period already in the first trimester. Based on the obtained ultrasound results, the further course and outcome of pregnancy can be predicted.

Ultrasound is indispensable for identifying possible pregnancy problems

8. Diagnosis of threatened miscarriage by ultrasound allows you to recognize early symptoms, which are characterized by a clear thickening of one of the walls of the uterine cavity, as well as a significant increase in the internal pharynx. According to ultrasound, with a possible miscarriage, the vital signs of the fetus and the state of the uterus and placenta as a whole are assessed.

9. Diagnosis of diseases and possible malformations of the female genital area (anomalies in the development of the vagina or uterus). Any deviation from the norm determines the course and outcome of pregnancy.

Typical signs and features of ovum implantation

Often, the ovum is attached to the wall of the uterus after a few days after the unprotected intercourse, and then the egg is introduced into the endometrial layer after fertilization. From this moment in the woman's body, the hormone CG (chorionic gonadotropin) begins to be actively produced, to which the pregnancy test strip reacts.

Ovum implantation

The screening test will not always be positive, therefore, it is necessary to resort to a reliable blood test to determine hCG. After receiving a positive test result, it is necessary as soon as possible to contact the gynecologist at the antenatal clinic for registration and further observation for nine months.

A formed ovum is the surest sign of pregnancy. It has a characteristic oval shape and is quite well visualized on ultrasound in the third week of absence of menstruation.

The embryo itself can be seen only when the term reaches the fifth week. If the ultrasound doctor does not detect the embryo in the ovum, then the study is repeated after about half a month. As a rule, the embryo becomes more clearly visible, and its heartbeat is also determined. In other cases, we are talking about pathological development or even about a frozen and undeveloped pregnancy.

That is why it is very important to undergo an ultrasound scan to exclude possible complications for further correcting the situation. The first trimester is the most important period of gestation, since throughout its entire length there is an active laying of all organs and systems of the unborn baby.

Terms of routine ultrasound diagnostics

According to the results of the WHO, strict periods have been determined for conducting mandatory ultrasound examinations during the gestation period of the unborn baby.

It is obligatory to perform three ultrasound screenings

At other time intervals, the examination behavior is prescribed strictly according to individual indications from the mother and the fetus:

recommended at 12-14 weeks;
for 20 - 24 weeks;
necessary at 32 - 34 weeks of gestation.

It is undesirable to neglect the term of the next examination, since it is during this period of gestation that it is possible to recognize fetal malformations. And if there is a forced need - interruption for medical reasons. The last screening examination can be carried out at a later time.

The results of current diagnostics may be significantly outside the normal range, but this is far from a cause for concern. Do not forget that the development of each child has its own characteristics. However, it is also not worth ignoring the identified symptoms.

Ultrasound during pregnancy has long been an understandable and familiar procedure, because it is the simplest, most reliable and informative method for monitoring the condition of the fetus. As a rule, a diagnostician during the study determines the duration of pregnancy, and almost every patient takes this for granted, without thinking - how exactly does the doctor determine the timing? And how accurate? What parameters does it use for this?

It is diagnostics with the help of ultrasound that helps doctors reliably determine the timing of bearing a child on the basis of indicators of a very different nature, but at the same time directly established for a more informative result.

Setting the exact due date also helps to predict the due date, which is very important both from a medical point of view and simply to calm the expectant mother. Knowing the most accurate time is also necessary in order to control the development of the fetus, its condition, the ratio of norms to reality.

How does the specialist determine the timing?

Some patients believe that it is enough for the doctor to look at the image on the monitor - and immediately the "age" of the child becomes visually clear, but this, of course, is not the case. The specialist records the received data of the embryo and compares it with the variants of the norm... Usually, to help the doctor, there is a special table with fixed indicators, which lists all the relevant norms by week.

Quantitative indicators.

Table No. 1. Rates of indicators at 5-10 weeks of gestation.

Table No. 2. Rates of indicators for the second trimester.


11	17-21	10-16	52-73
12	22-24	17-21	58-83
13	25-27	23-28	73-95
14	28-30	27-31	84-110
15	31-33	32-39	110
16	34-37	41-49	111-135
17	38-41	45-54	122-149
18	42-47	48-59	131-160
19	48-49	52-63	142-174
20	50-53	56-67	154-186
21	54-56	61-72	167-200
22	57-60	65-76	178-211
23	61-64	68-80	190-223
24	65-67	71-85	201-236

Table 3. Standards of indicators for the third trimester.

Pregnancy period (in weeks)	BPR (biparietal size) (in millimeters)	Frontal-occipital size (in millimeters)	Head circumference (in millimeters)
25	68-70	73-88	215-250
26	71-73	76-93	224-261
27	75-76	80-96	235-273
28	77-79	83-98	245-284
29	80-82	86-101	255-295
30	83-85	89-104	265-304
31	86-87	93-108	273-314
32	88-89	95-112	283-325
33	90-91	98-116	289-332
34	92-93	101-119	295-338
35	94-95	105-120	299-345
36	96-97	104-123	303-348
37	98-98	106-126	307-352
38	99-100	108-128	309-357
39	101-102	109-129	311-359
40	103	110-120	312-361

Table No. 4. Standards for the length of the fetus.

Pregnancy period (in weeks)	Embryo size (in centimeters)
5	0,8
6	1,1
7	1,3
8	1,5
9	2,2
10	3,2
11	4,1
12	5,3
13	7,5
14	8,7
15	10
16	11,5
17	13,1
18	14,2
19	15,2
20	16,5
21	26,6
22	27,8
23	29,8
24	31
25	34,6
26	35,5
27	36,5
28	37,7
29	38,6
30	39,8
31	41,1
32	42,5
33	43,6
34	45
35	46,1
36	47,3
37	48,6
38	49,8
39	50,6
40	51,7
41	52
42	53

Table 5. Standards for the abdominal circumference of the embryo.

Pregnancy period (in weeks)	Abdominal circumference (in millimeters)
11	40-61
12	50-71
13	58-79
14	66-91
15	91
16	88-115
17	93-130
18	105-144
19	114-154
20	125-163
21	137-177
22	148-190
23	160-201
24	173-223
25	183-228
26	194-240
27	206-253
28	217-264
29	228-277
30	238-290
31	247-300
32	258-314
33	267-334
34	276-336
35	285-344
36	292-353
37	300-360
38	304-368
39	310-375
40	313-380

Table No. 6. Norms of the thickness of the placenta.

Pregnancy period (in weeks)	The optimal value of the thickness of the placenta (in millimeters)
20	22-23
21	22,8-23,5
22	23,6-24,4
23	24,5-26
24	25,3-25,8
25	26,2-26,7
26	27-27,5
27	27,9-28,3
28	28,7-29
29	29,6-30
30	30,4-30,7
31	31,3-31,8
32	32,1-32,5
33	33-33,4
34	33,9-34,3
35	34,7-35
36	35,6-36
37	34,3-34,7
38	34,1-34,5
39	33,8-34
40	33,5-33,7

What exactly is the specialist analyzing?

The analyzed indicators of the norm depend on the trimester and the specific period.

In the first trimester, special attention is paid to the length of the fetus, since this is the only parameter that provides reliable information. During this period, there are no decisive differences in the development of embryos in different women, therefore, ultrasound establishes the "age" of the child with an accuracy of the day.

The second and third trimesters are periods during which absolute accuracy cannot be achieved, because from this moment the embryos begin to develop individually. Doctors use average figures, but even in this case, the period is set as reliably as possible, and it is very possible to identify possible pathologies. At the same time, specialists analyze such indicators as the circumference of the child's head, the diameter of the chest, the coccygeal-parietal distance of the embryo.

Now it is necessary to analyze in more detail the meaning of the indicators presented in the indicated tables, which may raise questions from patients.

Coccyx-parietal distance - the distance, respectively, from the crown of the embryo to the coccyx... Thanks to this indicator, the most accurate definition of the term is possible, because these sizes are universal. Also, if there are factors that impede the setting of the deadline, the CTE is the only reliable parameter in this case.

The diameter of the ovum is the directly fertilized egg, from which the embryo will develop in the future. Its size, of course, directly depends on the specific period and has been studied for a long time - it is enough for the doctor to look at the corresponding table.

The diameter of the yolk sac is also an important indicator. b, since the yolk sac plays a very important role throughout the development of the child (for example, in the first trimester it supplies the circulatory system of the embryo with nuclear erythrocytes). The dimensions are also always available in the table from the doctor.

Biparietal size- the distance between the parietal bones of the embryo.

Frontal-occipital size- the distance between the frontal and occipital bones, respectively.

Embryo length- is calculated when the child is in the maximum "unbent" state.

Placenta thickness- a lot depends on the placenta: it protects the child, and supplies him with everything he needs, and produces many hormones. Therefore, it is very important to check whether its thickness meets the deadline standards. If the mother's condition is stable, there are no deviations - by the thickness of the placenta, it is enough to simply establish the "age" of the embryo.

Accuracy

Many women are interested - how accurately does the ultrasound of the fetus help determine the timing of the weeks? Therefore, it is important to note that ultrasound diagnostics sets obstetric terms, in other words, the "age" of the embryo is calculated from the first day of the last menstruation. Sometimes a situation arises when a patient, while checking the tables on the Internet and the results of ultrasound, discovers differences in terms, so you need to know exactly which system was used to calculate, and not “sin” on the imperfection of ultrasound diagnostics.

Pathology

Ultrasound of the fetus is informative not only as an aid to determine the term, but also when pathologies of a different nature are detected. Moreover, some of them can be detected only with the help of ultrasound, it is also important to note that, since ultrasound can be done as often as you like, this is a fairly effective method of monitoring the condition of the fetus.

So, the main pathologies that can be determined are:

Development lag (detected by comparing the normative parameters with reality, indicators below the threshold indisputably indicate the presence of an anomaly).
Various defects (also detected when indicators do not match).
Low water.
Polyhydramnios.
Thickening of the placenta.
Non-developing pregnancy (indicators below the standards (especially the coccygeal-parietal size) in the first trimester).

When can I go to the diagnostic room?

Of course, modern ultrasound technologies make it possible to detect an embryo as early as a week after conception, but most clinics still have less perfect equipment. It is also important to note that this will require transvaginal ultrasound, which is very dangerous for the unborn child and can cause spontaneous miscarriage. So an early examination can be done only if there are special medical indications, in any other case, you can be patient with the knowledge of the exact time.

It is advised to contact a diagnostician at the 5th week of pregnancy, when it will already be possible to examine the fetus in more detail using an ultrasound scan, draw up certain conclusions and set the deadline with maximum accuracy.

Is it dangerous?

Some patients refuse ultrasound diagnostics with both transvaginal and transabdominal methods, citing the danger of ultrasound. Indeed, these fears are logical, because taking care of the baby's health is inherent in any mother. But ultrasound is absolutely not dangerous for the embryo, even at a short time there is no reason to believe that ultrasound waves will harm the development of the child, cause pathologies or cause miscarriage.

Error probability

Any woman can quite rightly think that the size of the embryo is not the most reliable indicator for setting the term, because each child develops in different ways and it is difficult to determine his exact age. But in fact, over the years of medical practice, there is no doubt about the correctness of the time period set on the ultrasound of the fetus.

If a woman still doubts the results of an ultrasound scan, you can always carry out a number of additional diagnostic procedures, which in turn will allow you to determine the timing at the most accurate level.

Fetal ultrasound is not only a method for monitoring the condition of the fetus, monitoring its development, but also a completely reliable, accurate, informative, convenient and simple way to determine the term by weeks. According to a variety of parameters that have been studied quite fully over the years of development of ultrasound medicine, the diagnostician quickly determines the obstetric "age" of the embryo, using special tables on which a simple patient can rely.

The yolk sac is the earliest visible part of the ovum. If it is visible on ultrasound, then this confirms the proper placement of the embryo. This is evidence that the egg has successfully implanted into the wall of the uterus, and the developing embryo has taken root in the womb, as it should be. So, the yolk sac: the norm by week.

The gestational sac and its role in the development of the embryo

The yolk sac is a membrane attached to the embryo on the ventral part. This formation provides early nutrition for the fetus. The gestational sac functions as the development of the cardiovascular system of the human embryo prior to the onset of internal circulation.

The fetal egg is the only structure available that can be used to determine the existence of an intrauterine pregnancy until the embryo can be identified. The yolk sac during pregnancy, if it develops normally, is visible in the early stages using ultrasound. The gestational sac determined at week 5 is a critical reference point for monitoring early pregnancy.

The normal functioning of the yolk sac is important at the beginning of embryonic circulation. The transport of blood to the walls of the sac occurs through the primitive aorta. Its circulation passes through a wide network of capillaries and returns through the yolk vein to the tubular heart of the embryo. Through this circulation, nutrients from the yolk are absorbed and transported to the embryo.

In the short term of pregnancy, ultrasound is performed to identify a viable embryo in the uterine cavity, confirm the gestational age, exclude the pathology of the embryo, or identify normal variants, for example, multiple pregnancies.

The initial sign of pregnancy is a thickening of the endometrium, but ultrasound does not allow us to say what exactly is causing this thickening.

When using a high-resolution transvaginal transducer, a fetal egg with a diameter of 1 mm is visualized in the uterine cavity 4 weeks and 2 days after the last menstruation with a regular menstrual cycle.

If menstruation is delayed for 5-7 days or more (gestation period is 5 weeks), a fetal egg with a diameter of 6 mm should be clearly defined in the uterine cavity. It has a clear rounded shape with an indistinct light rim along the periphery (hyperechoic rim - chorion). In this case, the level of beta-hCG blood is 1000-1500 IU / L (see What is hCG?). With a hCG level of more than 1500 IU / L, the ovum in the uterine cavity should be clearly visualized.

With a lower level of hCG, the ovum in the uterine cavity with transvaginal echography may not be detected. With a transabdominal study, the determination of the ovum in the uterine cavity is possible at a beta-hCG level of 3000-5000 IU / L.

Fig. 1Uterine pregnancy 4-5 weeks. Transabdominal scan.

IMPORTANT: gestational age cannot be accurately determined by the size of the ovum. Many tables on the Internet with the size of the ovum - determine the period very approximately (see table below).

From about 5.5 weeks, with transvaginal ultrasound, an extraembryonic structure, the yolk sac, begins to be visualized in the ovum. In this case, the level of beta-hCG is approximately an average of 7200 IU / L (see the norms of hCG during pregnancy).

Since the yolk sac is part of the embryonic structures, its detection makes it possible to distinguish the ovum from a simple accumulation of fluid in the uterine cavity between the sheets of the endometrium, and in most cases, makes it possible to exclude an ectopic pregnancy. The frequency of ectopic pregnancies is 1-2 per 2000-3000 pregnancies. Its risk increases with the use of assisted reproductive technologies (ART). It is necessary to suspect an ectopic pregnancy when the hCG level is more than 1500 IU / L, and the ovum in the uterine cavity is not detected.

Fig. 2Pregnancy 5.5 weeks. The yolk sac is determined. Transvaginal scanning.

From 6 weeks of pregnancy (sometimes a little earlier), an embryo can be identified in the ovum, about 3 mm long. Since the same time, most ultrasound devices can determine the heartbeat of the embryo. If the heartbeat is not detected or is indistinct when the embryo length (CTE) is 5 mm, a second ultrasound is shown in a week. Lack of cardiac activity during this period is not necessarily a sign of fetal distress or missed pregnancy.

The numerical values of the heart rate in the embryo in uncomplicated pregnancy gradually increase from 110-130 beats / min at 6-8 weeks of gestation to 180 beats / min at 9-10 weeks.

The length of the embryo is measured from the head to the tail end, and is designated under the term KTP (coccygeal-parietal size), in eng. literature - CRL (Crown-Rump Length). It should be noted that the coccygeal-parietal size of the embryo is less subject to individual fluctuations than the average inner diameter of the ovum, and therefore, its use to determine the gestational age gives better results. The error in this case usually does not exceed ± 3 days. With clear visualization of the embryo, the gestational age is established depending on its length, and not on the size of the average internal diameter of the ovum (SVD).

For correct measurement of the coccygeal-parietal size of the embryo, its clear visualization is necessary. In this case, one should strive to measure the maximum length of the embryo from its head end to the coccyx.

In the normal course of pregnancy, the diameter of the ovum increases by 1 mm per day. Smaller growth rates are a poor predictor. With a gestation period of 6-7 weeks, the diameter of the ovum should be about 30 mm.

Table 1. Dependence of gestational age on the average inner diameter of the ovum (D), M. N. Skvortsova, M. V. Medvedev.

Table 2. Normal values of the coccygeal-parietal size (CTE) depending on the gestational age (full weeks + days), given in millimeters, the lower limit is the 5th percentile, the upper limit is the 95th percentile.

It should be emphasized that the determination of the gestational age by the length of the CTE is best done before 12 weeks of pregnancy. At a later date, the measurement of the biparietal diameter, head and abdominal circumference should be used.

Fig. 3 Pregnancy 12 weeks 3 days.

The motor activity of the embryo is determined after 7 weeks of pregnancy. At first, these movements are very weak and single, barely distinguishable during examination. Then, when it becomes possible to differentiate into the head and pelvic ends of the embryo, the movements resemble flexion and extension of the trunk, then separate movements of the limbs appear. Since the episodes of the embryo's motor activity are very short and are counted in seconds, and the periods of motor rest can be significant in time, the registration of the embryo's cardiac activity is undoubtedly a more important criterion for assessing its vital activity.

The diagnosis of anembryonia (empty ovum) is assumed if the yolk sac is not detected in a 20 mm ovum. Or if a fertilized egg with a diameter of more than 25 mm with a yolk sac does not contain an embryo. And also with a yolk sac of 10 mm or more. In any case, if anembryonic disease is suspected, all the data obtained should be interpreted in favor of pregnancy, and the study should be repeated after 7 days.

The diagnosis of a non-developing pregnancy should not be made if, with an ultrasound scan, the ovum is less than 20 mm in size. With an embryo length of 5 mm or more, in most cases, the heartbeat should be clearly defined. If the embryo is less than 5 mm, the ultrasound should be repeated a week later. If, on a second study after a week at CTE = 5-6 mm, cardiac activity is not determined, pregnancy is not viable. The diagnosis of non-developing pregnancy can be confirmed by the discrepancy between the level of beta-hCG and echographic data.

It should be noted that the frequency of abortion in the normal population is 15-20% of all clinically diagnosed pregnancies. However, in reality, if you count all "chemically" diagnosed pregnancies, determined by the level of beta-hCG before the expected next period, the frequency of miscarriages can reach up to 60%.

Best regards, doctor of ultrasound diagnostics, Barto Ruslan Aleksandrovich, 2012

Setting the exact due date also helps to predict the due date, which is very important both from a medical point of view and simply to calm the expectant mother. Knowing the most accurate time is also necessary in order to control the development of the fetus, its condition, the ratio of norms to reality.

How does the specialist determine the timing?

Quantitative indicators.

Table No. 1. Rates of indicators at 5-10 weeks of gestation.

Table No. 2. Rates of indicators for the second trimester.


11	17-21	10-16	52-73
12	22-24	17-21	58-83
13	25-27	23-28	73-95
14	28-30	27-31	84-110
15	31-33	32-39	110
16	34-37	41-49	111-135
17	38-41	45-54	122-149
18	42-47	48-59	131-160
19	48-49	52-63	142-174
20	50-53	56-67	154-186
21	54-56	61-72	167-200
22	57-60	65-76	178-211
23	61-64	68-80	190-223
24	65-67	71-85	201-236

Table 3. Standards of indicators for the third trimester.

Pregnancy period (in weeks)	BPR (biparietal size) (in millimeters)	Frontal-occipital size (in millimeters)	Head circumference (in millimeters)
25	68-70	73-88	215-250
26	71-73	76-93	224-261
27	75-76	80-96	235-273
28	77-79	83-98	245-284
29	80-82	86-101	255-295
30	83-85	89-104	265-304
31	86-87	93-108	273-314
32	88-89	95-112	283-325
33	90-91	98-116	289-332
34	92-93	101-119	295-338
35	94-95	105-120	299-345
36	96-97	104-123	303-348
37	98-98	106-126	307-352
38	99-100	108-128	309-357
39	101-102	109-129	311-359
40	103	110-120	312-361

Table No. 4. Standards for the length of the fetus.

Pregnancy period (in weeks)	Embryo size (in centimeters)
5	0,8
6	1,1
7	1,3
8	1,5
9	2,2
10	3,2
11	4,1
12	5,3
13	7,5
14	8,7
15	10
16	11,5
17	13,1
18	14,2
19	15,2
20	16,5
21	26,6
22	27,8
23	29,8
24	31
25	34,6
26	35,5
27	36,5
28	37,7
29	38,6
30	39,8
31	41,1
32	42,5
33	43,6
34	45
35	46,1
36	47,3
37	48,6
38	49,8
39	50,6
40	51,7
41	52
42	53

Table 5. Standards for the abdominal circumference of the embryo.

Pregnancy period (in weeks)	Abdominal circumference (in millimeters)
11	40-61
12	50-71
13	58-79
14	66-91
15	91
16	88-115
17	93-130
18	105-144
19	114-154
20	125-163
21	137-177
22	148-190
23	160-201
24	173-223
25	183-228
26	194-240
27	206-253
28	217-264
29	228-277
30	238-290
31	247-300
32	258-314
33	267-334
34	276-336
35	285-344
36	292-353
37	300-360
38	304-368
39	310-375
40	313-380

Table No. 6. Norms of the thickness of the placenta.

Pregnancy period (in weeks)	The optimal value of the thickness of the placenta (in millimeters)
20	22-23
21	22,8-23,5
22	23,6-24,4
23	24,5-26
24	25,3-25,8
25	26,2-26,7
26	27-27,5
27	27,9-28,3
28	28,7-29
29	29,6-30
30	30,4-30,7
31	31,3-31,8
32	32,1-32,5
33	33-33,4
34	33,9-34,3
35	34,7-35
36	35,6-36
37	34,3-34,7
38	34,1-34,5
39	33,8-34
40	33,5-33,7

What exactly is the specialist analyzing?

The analyzed indicators of the norm depend on the trimester and the specific period.

In the first trimester, special attention is paid to the length of the fetus, since this is the only parameter that provides reliable information. During this period, there are no decisive differences in the development of embryos in, therefore, ultrasound establishes the "age" of the child with an accuracy of the day.

Now it is necessary to analyze in more detail the meaning of the indicators presented in the indicated tables, which may raise questions from patients.

Biparietal size- the distance between the parietal bones of the embryo.

Frontal-occipital size- the distance between the frontal and occipital bones, respectively.

Embryo length- is calculated when the child is in the maximum "unbent" state.

Accuracy

Pathology

Ultrasound of the fetus is informative not only as an aid to determine the term, but also when pathologies of a different nature are detected. Moreover, some of them can be detected only with the help of ultrasound, it is also important to note that, since ultrasound can be done as often as you like, it is a fairly effective method of monitoring the condition of the fetus.

So, the main pathologies that can be determined are:

Development lag (detected by comparing the normative parameters with reality, indicators below the threshold indisputably indicate the presence of an anomaly).
Various defects (also detected when indicators do not match).
Low water.
Polyhydramnios.
Thickening of the placenta.
Non-developing pregnancy (indicators below the standards (especially the coccygeal-parietal size) in the first trimester).

When can I go to the diagnostic room?

Is it dangerous?

Error probability

What is SVD during pregnancy and how to determine it on ultrasound? There is only one answer to this question.

SVD is the average inner diameter of the ovum according to ultrasound diagnostics. This indicator is measured exclusively in millimeters.

Ovum illustration

Indicative indicators of SVD, depending on the timing of gestation

When the diameter of the ovum is approximately 4 millimeters, then the gestational age is. It is possible to assume that about four weeks have passed since the day of conception.
Closer to the fifth week, the diameter will reach 6 millimeters.
After a few days, the fetus becomes 7 millimeters.
the diameter increases to 12 - 18 millimeters.
The average SVD value for a period of six weeks and five days is 16 millimeters.

Fetal egg for ultrasound

Ultrasound examination at a short period of gestation

Diagnostics are carried out for the following purposes:

Diagnostics of the localization of the ovum

2. Determination of single or multiple pregnancy is not difficult. In the uterine cavity, there are two or more fetuses with active life.

3. Assessment of the main sizes of the ovum and embryo and their comparison with the indicators of the norm.

4. Study of the correct structure of the embryo and ovum to exclude serious congenital malformations. These can be chromosomal mutations (for example, Down's syndrome).

6.. This small cystic formation provides the mother-to-be with important hormones to preserve the fetus in the early stages of development.

Ultrasound is indispensable for identifying possible pregnancy problems

Typical signs and features of ovum implantation

Ovum implantation

A formed ovum is the surest sign of pregnancy. It has a characteristic oval shape and is quite well visualized on ultrasound in the third week of absence of menstruation.

Terms of routine ultrasound diagnostics

According to the results of the WHO, strict periods have been determined for conducting mandatory ultrasound examinations during the gestation period of the unborn baby.

It is obligatory to perform three ultrasound screenings

At other time intervals, the examination behavior is prescribed strictly according to individual indications from the mother and the fetus:

recommended at 12-14 weeks;
for 20 - 24 weeks;
necessary at 32 - 34 weeks of gestation.

The presence of the ovum in the uterus eliminates the possibility of an ectopic pregnancy. In multiple pregnancies, two separate ovules can be seen.

How long can you see the fertilized egg.

Fertile egg: size by week

The sizes of the average inner diameter of the ovum by week are given in the calculator.

Irregularly shaped fertilized egg (deformed fertilized egg)

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

Empty fetal egg

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

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

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

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

If the doctor during an ultrasound found a fertilized egg in the uterine cavity, then you can congratulate the woman on the onset of pregnancy. This formation in the uterine cavity is the very first and most important sign of the development of pregnancy.

The formation contains the embryo, as well as the amniotic fluid. Depending on what shape, size and location the structure has, the doctor determines the nature of the course of pregnancy.

Having learned about their pregnancy, many curious expectant mothers begin to ask the doctor questions about how and for how long the fertilized egg is visible and how it looks. We will try to answer them.

The fertilized egg, the diameter of which is very small in the first days of pregnancy, can be seen as early as two to three weeks after a delay in menstruation. The formed structure in most cases is located in the upper part of the uterine cavity, has a dark (gray) shade and a round or oval shape. The embryo at this time is still microscopic in size, so when it is not detected.

Development and structure

The growth of the ovum begins from the moment of conception. The fertilized egg begins to move along the fallopian tube, during which the cells are cleaved. Making its way to the uterus, the fertilized crushing egg needs nutrients and oxygen, therefore, a week later, a chorion begins to form from above, which is subsequently transformed into.

The surface of the chorion has villi that help the formation attach to the uterus. In the future, these villi are contained only at the site of implantation of the formation into the wall of the uterus. The rest of the structure loses villi and remains smooth. Chorion provides the fetus with all vital functions, one of which is protection against infections.

A value less than 7 mm indicates the onset of the middle of the fifth week. This is one of the most important periods when there is an active formation of blood vessels, heart and nervous system. The embryo is usually 2 mm in size.

When an ultrasound scan shows a 10 mm ovum, this indicates that the heart and blood vessels are already fully formed and the embryo has a neural tube with a slight thickening at the end (future brain).

6 obstetric week visualizes a value of 12 mm. At the 6th obstetric week, the ovum is 12 mm in size, has a spherical shape, the embryo looks like a white strip about 5-6 mm long. At this point, the heart rate is 110-130 per minute. If any deviation is detected during the sixth week, a re-examination is recommended after a week.

To correct the situation, doctors remove and then the egg takes the correct shape. What a fertilized egg looks like during miscarriage depends on the gestation period. At 1-2 weeks, a miscarriage may look like the bleeding of your period. At a later date, the formation looks like a blood clot. If a miscarriage occurs within 7-9 weeks, then the woman may find pieces of fetal tissue.

If the structure is oval and at the same time flat, this may also indicate. However, in the absence of pain and other ailments, it makes sense to continue monitoring the pregnancy. Re-examination will allow the doctor to draw the correct conclusion.

Wrong location

A low ovum does not indicate a serious pathology, but requires more careful monitoring throughout pregnancy. If the formation is very close to the cervix, then a cervical pregnancy may occur, which is fraught with the removal of the uterus.

Empty fetal egg

When you can find an empty fertilized egg, when there is only liquid or a blood clot inside the cavity.

Types of ultrasound. What are SVD and KTR?

To determine the parameters of the ovum, various types of ultrasound are performed:

Transabdominal - examination takes place through the external abdominal wall.
Transvaginal - the examination is carried out through the vagina.

With TA examination, a clear identification of the formation is possible starting from the 5th obstetric week. At this time, the ovum is 5-8 mm in size. Using the second research method, it is possible to determine the size of the ovum on 3-6 days of delayed menstruation, and this is 4-5 weeks of gestation. The embryo is visualized starting from the 5th week of pregnancy with a TV examination, and with TA - from the 6th week in the form of a linear formation.

To assess the size and growth of education and embryo, indicators such as:

SVD is the average inner diameter of the ovum.
CTE is the coccygeal-parietal size of the embryo / fetus.

SVD shows the size of the ovum by week and is measured in millimeters. So the indicator of the size of the ovum by weeks of pregnancy constantly varies, the CTE indicator is more accurate for determining the reliable gestation period. In this study, the error can be up or down three days. Basically, the study is carried out up to 12 weeks of gestation.

The size of the ovum helps to quickly determine how long the pregnancy is and how the fetus is developing in the womb. The first three months of development are the most important, because it is at this time that all organs and systems of the unborn baby are actively laid. Accordingly, it is important to undergo a scheduled ultrasound on time, which helps to identify possible deviations and to carry out the optimal correction of the current situation.

This is how our consciousness works: for thousands of years, women have carried their children without thinking at all about any 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, since then science has made great strides. Fetal ultrasound is now done to every pregnant woman, and more than once. And just in the results of this examination, many find that the fetus has some kind of yolk sac (sac, as many affectionately call it). And, of course, it becomes interesting where it came from, why it is needed and where it is located in an adult.

The yolk sac is formed at the beginning of the third week from an endoblastic vesicle (a derivative of an endoblast). It does not function for long - about three months, but it 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 together with the developing embryo.

Why do you need a yolk sac?

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

WITH 18 -th of the day 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.

WITH 28 -th of the day the walls of the yolk sac produce the first germ cells, which will move a little later to the embryonic gonadal primordia. It is important to note that the eggs of the future girl are laid at this time. If at this stage the mother has been ill or experienced severe stress, the laying of the eggs will not occur correctly and in the future the adult woman will suffer from infertility.

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

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

And where does the yolk sack 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 ahead of time, 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 determines the development of a frozen pregnancy and spontaneous abortions.

And what about the 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 measure:
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 it mean that the yolk sac is not visualized?

The yolk sac is formed 15-16 days after conception and ceases to function at the end of the first trimester - 11 weeks of gestation. 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, contracts and remains only in the form of a cystic formation near the base of the umbilical cord. Yolk bag v the norm visualized with 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 (at the 7th week from 4-5 mm), gradually increases to 10 mm, and then its reverse development begins.

If the yolk sac is not visible at 6 to 11 weeks:- It may be that you have incorrectly set the gestational age, and the pregnancy is less than 6 weeks (up to 6 weeks, the yolk sac is not visualized normally). In this case, 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 result in an abortion 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 ensure the presence or absence of a yolk sac. - After 12 weeks it is normal if the yolk sac is not detected. This means that the fetus has begun to receive nutrients through the placenta.

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 early 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 associated with the embryonic intestine. This formation is formed from the cells of the mesoderm and has the shape of a ring with thin walls.

Basic 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 to each other. First, this structure is a source of nutrients. Secondly, the yolk sac is actively involved in the respiration process.

At about 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 main ones 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 with spontaneous abortion.

Where does the yolk sac go?

Every expectant mother knows that the vital activity of the fetus directly depends on the functioning and state of the placenta. But where does the yolk sac go? In 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 the increase in the yolk sac dangerous?

Since this structure is very important, it is quite natural that it is precisely this structure that is examined during an ultrasound examination. You can see her starting from the sixth week from conception. The yolk sac can no longer be examined with 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 related to diet, certain medications, or severe stress. In any case, with similar ultrasound results, you need to go to a gynecologist. Only a specialist knows why the yolk sac can be enlarged, what this means and whether special treatment is required.