Expanded collar zone in the fetus. What is TVP on ultrasound during pregnancy. What is the indicator - TVP

In the first trimester, during which the norm of the collar space at 12 weeks plays an important role.

The determination of TVP in combination with biochemical markers is today considered one of the main criteria for the formation of a risk group with chromosomal pathologies. It is believed that a certain period is considered the most informative period, and after 13 weeks of pregnancy, such a study does not provide any information.

Collar space is the accumulation of fluid in the neck of the fetus

The collar space is the accumulation of a certain amount of fluid in the neck of a developing fetus. In fact, the presence of a small volume of such fluid is normal for a developing person, but with Down syndrome, an excess of the norm is noted.

You should be aware that measuring only one collar space is not enough to confidently assert that a child has a chromosomal disease. To assess the image of the collar space in medical practice, both transabdominal and transvaginal scanning are used. The risk of diagnosing chromosomal abnormalities in a child is higher if a large width of the collar space is diagnosed.

The size of the collar space itself is not a sentence, but only indicates the presence of a certain risk.

It is possible to draw conclusions about the increased risk of developing chromosomal diseases in a child only if the results are poor and if the size of the neck fold is above 3 mm. In such a situation, to clarify the diagnosis, a chorion biopsy is performed, which makes it possible to refute or confirm the presence of a chromosomal disease in the fetus.

Features of TVP measurement

Experts say that the optimal time for measuring TVP is 12 weeks. Compliance with just such terms is associated with the fact that an ultrasound scan earlier or later than the proposed dates may not carry diagnostic value due to the receipt of incorrect data.

Measuring TVP up to 12 weeks has some difficulties and this is due to the small size of the fetus. Performance after 12 weeks is undesirable, since after this time the fluid accumulated in the collar region can be actively absorbed by the child's lymphatic system, which began to develop with accelerated force.

It is important to remember that before starting the measurement of TVP, it is necessary to determine the exact gestational age.

For this purpose, the specialist determines the coccyx - the parietal size of the developing fetus.

To measure TVP according to all the rules, the following conditions must be met:

ultrasound should be performed at 12 weeks
it is important to observe the sagittal plane along which the scanning process will be performed
KTR size should be equal to 45-84 mm

It should be remembered that the position of the fetus during the procedure can have a significant confluence on the results of the measurement of TVP. The TVP indicator can be increased by 0.6 mm if the child straightened his head. When the child presses the chin to the chest, a decrease in the indicator to 0.4 mm can be observed. It is for this reason that it is possible to speak about the reliability of the measurements obtained only if the measurement took place with the correct position of the child.

Normative indicators of TVP

During pregnancy, when performing ultrasound at 12 weeks, the norm of TVP should be 0.7-2.5 mm. In the event that a thickening of the collar space is observed, then the likelihood of the birth of a baby with chromosomal pathologies increases. It is for this reason that with a TVP of 3 mm or more, an invasive karyotyping is prescribed by a specialist.

Thanks to this type of research, it is possible to diagnose at the cellular level the probability of having a child with a genetic syndrome. In addition, a chorionic villus biopsy is performed, when a piece of placental tissue is taken for research.

It is also possible to confirm the risk of a child with chromosomal abnormalities in parents with the help of early amniocentesis, when a sample of amniotic fluid is taken.

It is important to remember that the risk of diagnosing various abnormalities in a baby increases with the age of the expectant mother. When the collar space is thickened, the specialist pays attention to the size of the nasal bone, because with pathologies of a chromosomal nature, there is a discrepancy between its size and the term. In addition, with such deviations, a shortened upper jaw can be diagnosed, which makes the contours of the face smooth.

Chromosomal pathologies and abnormalities in TVP

The risk of developing chromosomal abnormalities in the unborn child is directly proportional to the increase in TVP.

Medical practice shows that the following pathologies are most often diagnosed:

Down syndrome
Patau Syndrome
Turner syndrome
Edwards syndrome

Diagnosis of such disorders is associated with trisomy, when an extra chromosome is determined. In addition, monosomy is possible, which is characterized by the absence of one chromosome. If complex defects incompatible with life are revealed in the expectant mother, she is offered an artificial termination of pregnancy. When determining Down syndrome, parents have the right to independently decide whether to terminate the pregnancy or continue it.

An increase in the size of the collar space has a direct relationship with genetic chromosomal defects and congenital malformations.

At the same time, it is not necessary to completely equate the increase in TVP with the obligatory termination of pregnancy, because parents often give birth to completely healthy children without any defects and deviations. The expansion of the collar space is considered only one of the indications for a more detailed examination of the expectant mother, which will allow diagnosing congenital malformations.

Useful video - 12 weeks of pregnancy: the development of mother and baby.

Particular attention is paid to the collar space thickness (TVP), the value of which correlates with the presence fetal chromosomal disorders(First of all, it concerns). Therefore, the definition of TVP, together with today, is one of the main criteria for the formation of a risk group for chromosomal pathology. Collar space- This is the area between the inner surface of the skin of the fetal neck and the outer surface of the soft tissues that cover the cervical spine. TVP measurement is carried out at the following mandatory conditions:

strictly sagittal scanning the fetus / embryo (the sagittal plane goes from front to back and divides the human body into two symmetrical parts);
gestational age 10-14 weeks with numerical values (KTR) from 45 to 84 mm.

Determination of TVP using ultrasound

During pregnancy, women undergo an ultrasound examination and with the help of it, TVP is determined. The procedure is prescribed once a trimester and it is aimed at identifying pathologies. To determine them, sonographic markers are measured in the fetus. The obtained parameters correspond with the norm. The most important is the study in the first trimester, then these markers lose their relevance.

During the first trimester, measure:

limb length;
profile bones;
collar space thickness.

To implement the last of the listed measurements, the ultrasound doctor, using a sensor, directs a sound wave to the neck area under the back of the head or to the first spine and takes readings. In this place, subcutaneous fluid accumulates between the skin and bone tissues of the embryo. Its presence can indicate both a normally developing pregnancy and deviations in the unborn child. Later, the amount of fluid gradually decreases, and the result of the study loses its information content.

For accurate diagnosis, when measuring the thickness of the collar space, several conditions must be met:

The pregnant woman is in a prone position;
The fetus is located in a convenient position for research. A lateral position is considered appropriate when the profile can be analyzed. If the desired position is not occupied, then a transvaginal examination is performed.
The ratio of the coccygeal-parietal size;
Compliance with the terms of diagnostics;

In addition, the specialist must be competent in the issue of TVP. And also an important role is played by the apparatus with which the diagnosis is carried out.

When measuring the collar, two rules are also observed:

Accounting for the thickness of the amniotic membrane;
Doppler use.

Norms of the thickness of the collar space

Medical statistics on the thickness of the collar space at various stages of pregnancy are presented in the following table.

Important Values greater than the 95th percentile are accepted as deviations from the norm.

The likelihood of developing chromosomal diseases

The likelihood of chromosomal abnormalities is directly proportional to the increase in TVP, with the most common pathologies such as:

(trisomy on chromosome 21, more than 50%);
(trisomy on chromosome 18, ?25%);
(monosomy on the X chromosome, ?10%);
(trisomy on chromosome 13, ?5%), etc.

Trisomy is the presence of an extra chromosome, and monosomy- the absence of a chromosome in the chromosome set. The dependence of chromosomal abnormalities on the value of TVP (study P. Pandya) is presented in the table.

If TVP is abnormal

At the moment, the optimal for the formation of a risk group for chromosomal abnormalities is a combined examination, including the determination of TVP by , analysis ( β- PAPP-A in the blood serum of a pregnant woman) and. After it, a conclusion is made, in which the risk for chromosomal abnormalities is noted (for example, a combined risk of 1:300). If there is a high risk, a woman is recommended to make ( sampling) to determine the chromosomal set of the fetus. It may also be offered cordocentesis(cord blood sampling) or chorionbiopsy(collection of material from chorionic villi).

Information It should be remembered that these examination methods are performed only with the informed consent of the pregnant woman, and every woman has the right to refuse them!

With a normal chromosome set (23 pairs of chromosomes), pregnancy is prolonged in the usual way. In the presence of severe chromosomal diseases that are incompatible with life, a woman is strongly recommended to terminate the pregnancy. In the presence of Down syndrome, the family can independently decide on the future fate of the unborn child (prolong the pregnancy, or terminate it). Thus, the definition of TVP is fundamental for, as it makes it possible to diagnose fetal chromosomal pathology in time and make the correct and informed decision about each specific pregnancy.

If the thickness of the collar space is increased

With increased TVP, a woman is included in the risk group. Depending on the other indicators, this will be a group of medium or high degree. The most common abnormalities associated with TVP expansion are chromosomal:

Down syndrome
Patau Syndrome
Turner syndrome
Edwards Syndrome.

In addition to the wrong number of chromosomes, the size of the neck fold can be affected by:

Heart defects
Improper circulation of lymph
Anomalies in the development of connective tissues
Deviations in the formation of bone structures

It may also be associated with a complicated course of pregnancy:

Anemia
taxoplasmosis
Cytomegalovirus
Parvovirus.

With an unfavorable result, a woman is recommended to undergo an ultrasound scan every four weeks to track growth or, conversely, reduce fluid in the cervical region. In addition, expectant mothers who are at risk are assigned a genetic consultation to clarify possible pathologies.

The specialist studies the anamnesis, calculates the percentage of probability by correlating:

ultrasound indicators;
the result of a biochemical blood test;
mother's age.

If TP is increased An additional blood test and a second ultrasound examination may be ordered. With secondary confirmation and a risk ratio of 1:300, further studies are recommended:

Amniocentosis. Intake of amniotic fluid;
Chorionic biopsy. Taking for analysis the cells that form the placenta;
Placentobiopsy. Collection of placental cells;
Cordocentesis. Taking for analysis of umbilical cord blood or material from the villi of the embryo.

The result of each procedure, unlike the previous ones, gives one hundred percent clarity on the presence of pathologies of TVP in the fetus.

After receiving the data, the pregnancy is prolonged or recommendations are given for termination for medical reasons. The choice is up to the future parents.

Features of the thickness of the collar space at 12 weeks

At the twelfth week, the embryo has already passed three months of development and the main markers by which conclusions can be drawn about its development are visible to the specialist. This is the most informative stage for determining various pathologies and abnormalities in the development of the fetus, as well as during pregnancy in general. Each parameter has its own data, which correlate with the norm table. As for the collar zone, its thickness also has indicators with certain limits. The accumulation of fluid, giving a fold at the twelfth week, should not exceed 3 millimeters, the minimum size is 0.7 mm. It is important to keep in mind that the data may vary depending on the location of the fetal head: it is pressed against the chest, turned to the side, etc.

Features of TVP at 13 and 14 weeks

In the second trimester, at 13-14 weeks of gestation, the cervical fold decreases in size. The indicator is gradually becoming irrelevant. At week 13, an indicator from 1.7 to 4 mm can be put in the form with the baby's data, in the line with data on TVP. These figures are within the accepted range and the risk of developing pathology in the embryo or pregnancy complications in the mother is reduced to a minimum percentage.

The expansion of the collar zone does not always indicate the development of problems in the fetus. It is important to know that its dimensions are always correlated with the indicators of other echographic markers obtained by ultrasound. If, nevertheless, the dimensions of the TVP have gone beyond the boundaries of normal, you should not despair. There can be many reasons. In each case, they are determined by a specialist with a specific qualification. And depending on the identified anomalies, further actions can be assigned. It should not be forgotten that the result of measuring the collar zone is relevant only during the first trimester. Try not to miss this time.

Pregnant women have to keep in mind a lot of parameters that speak about the development of the child. TVP is one of them.

What is TVP?

TVP stands for "collar space thickness". The collar space, or cervical fold, is the accumulation of fluid under the skin of the fetus in the occipital (back) of the neck. The collar space at 11 weeks is not the most important, but not the least important indicator of the normal development of the child. After 13-14 weeks, the subcutaneous fluid is gradually absorbed by the child's lymphatic system, and the measurement of this parameter ceases to be significant, as, for example, the measurement of TVP at 11 weeks.

The control of TVP at 11-12 weeks occurs by ultrasound - in other words, using a conventional ultrasound (sometimes, however, it is required to undergo a vaginal ultrasound). The specialist measures the length of the fetal body and the thickness of the collar space, and based on the data obtained, draws preliminary conclusions about the development of the child. The results of conventional and vaginal ultrasound can give different indicators of TVP. This is due to the fact that different devices "see" the child in different ways.

What is the significance of measuring the collar zone at 11 weeks, and is it possible to make a final diagnosis based on it? Strictly speaking, deviations from the norm (see below) in the thickness of the collar space for a period of 11 weeks does not indicate the presence of pathology in development. TVP is measured to determine the risk group who will need additional research for the presence of Down syndrome in a baby. By itself, the thickened collar space still does not say anything.

According to statistics, only 7% of children in whom the thickness of the collar space differed from the norm for a period of 11 weeks were born with Down syndrome. Do not panic if an additional examination is required - this is not a sentence for the child at all!

Normal TVP at 11 weeks

At week 11, the fetus has a size of 50-60 mm. At the same time, the reflective TVP at 11 weeks is as follows: 1-2 mm. It remains the same at week 12, and at week 13, the last week, when the TVP is important, the collar zone increases to 2.8-3 mm. The thickness of the collar space is more than 3 mm - a deviation from the norm. In this case, the woman is sent for examination. To confirm the diagnosis of "Down's syndrome", it is not enough to measure TVP alone. You will also need a triple test, a chorionic villus biopsy and other tests. If the ultrasound was performed transvaginally, the normal collar zone at 11 weeks is no more than 1.8 mm, at 13 weeks it is no more than 2.5 mm.

Even after several tests confirming fears about a thickened collar space at 11 weeks, it is impossible to say for sure that the child has Down syndrome. The only accurate diagnostic method is amniocentesis (examination of amniotic fluid), but it is not recommended before 16 weeks. In rare cases, TVP values can exceed 4 or even 5 mm. But even with such an excess of the TVP norm at 11 weeks, there is a very real chance of giving birth to a healthy baby - almost 50%.

What to do if TVP at 11 weeks is higher than normal?

As mentioned above, the main thing is not to panic and not invent all sorts of horrors. Stress is harmful to the expectant mother and the child, who before that was quite healthy and developed normally. Usually, TVP is measured at 11 weeks in case of deviation from the norm, it is carried out two or three times. Sometimes (in 10% of cases) it turns out that the cause of deviations in the thickness of the neck fold is the umbilical cord, wrapped around the fetal neck, obscuring the "view" for the device. In this case, the measurement is carried out at the borders of the umbilical cord, and then the average value is calculated.

If the doctor sees that the indicator "thickness of the collar space 11 weeks" exceeds the norm, he also measures the length of the nasal bone of the fetus. This parameter is used not only for suspected Down syndrome, but also for Patau (extra chromosome 13), Edwards (extra chromosome 18) and Turner (X-chromosome defect) syndromes. Thus, TVP can become a signal for a comprehensive examination, including an assessment of blood flow. This is especially important for expectant mothers with late pregnancy.

An increase in the collar zone at 11 weeks indicates the presence of any of the listed chromosomal pathologies even less often than a Down's symptom. So, Edwards syndrome is found only in 24% of children with an enlarged cervical fold, Shereshevsky-Turner syndrome - in 10%, and Patau syndrome - in less than 5% of children.

Do not write off the measurement error. Of course, modern equipment allows you to give high-precision results, but even it is powerless if, for example, the fetus has strongly bent or unbent the head. It is clear that it is not always possible to "catch the moment" when the child's head is fixed in a neutral position. Incorrectly or inaccurately measured nuchal thickness at 11 weeks is one of the most common reasons for re-examination and, unfortunately, another cause for concern.

What if other tests confirmed the risk of pathology in the child, as indicated by TVP at 11-13 weeks? The choice is for the woman. She may agree to an amniocentesis, but this procedure is fraught with risk to the fetus, especially in the early stages. It is worth agreeing to it if there is a predisposition to deviations (there were similar cases in relatives; the woman is over 35 years old; there were chromosomal abnormalities during a previous pregnancy; ultrasound revealed defects in the development of the internal organs of the child). In any case, the decision must be made only after weighing all the pros and cons and discussing this problem with a doctor and loved ones. But you can’t give in to pressure and act against your will - most often, female intuition tells you how to do the right thing.

The measurement of TVP should not instill undue anxiety in the expectant mother. The chances that the child will be born healthy are high, and an appointment for additional tests is not a sentence.

When carrying a fetus, a woman has to undergo many medical examinations. One of them is fetal TVP. The term is deciphered by the phrase "collar space thickness" - this is the amount of fluid that accumulates on the fetal neck in a special skin fold. Its presence is a phenomenon characterized as a norm if it does not exceed certain limits. On ultrasound, this parameter is determined only in a strictly limited period - from 10 to 14 weeks of pregnancy.

The width of the collar space is directly related to the chromosomal abnormalities of the embryo, i.e. deviations in its development due to changes in DNA. Usually, such violations are detected immediately by the maternal organism itself - then miscarriages occur.

If the anomalies appear at a later date, babies survive, but are born with various genetic diseases. That is why the determination of fetal TVP at 12 weeks is an important point in the course of pregnancy.

How is TVP checked?

As mentioned above, the determination of the size of the collar space is carried out only in a strictly defined period.

This is due to the following reasons:

The area at the back of the head of the embryo increases by weeks, starting from the 10th. Until that time, there is simply nothing to explore.
After the 14th week, all the accumulated fluid is absorbed by the lymphatic system, the collar fold disappears, and ultrasound becomes pointless.

Measurement of the size of the cervical fold of the fetus is performed by ultrasound. The pregnant woman is laid on the couch in the “back down” position. The ultrasound machine has a special sensor that is lubricated with a gel that increases the conductivity of the waves.

There are two types of ultrasound:

Transabdominal, in which the sensor of the ultrasound machine is outside: the doctor leads it along the abdominal region, having previously lubricated the woman's stomach with the gel.
The transvaginal method is suitable for situations where it is difficult to determine the location of the fetus. Then the sensor, with a condom put on it and a gel applied, is immersed in the vagina.

Having received the necessary data, the doctor compares the indicators of fetal TVP by week.

Table of TVP norms by week

If the child does not have developmental anomalies, then ultrasound will show an expansion of the collar space of no more than three millimeters with the transabdominal method and no more than two and a half millimeters with the transvaginal one.

What does the weekly rate table show? As an example, we can analyze the TVP data for the 12th week. In women expecting a healthy child, the value of the collar zone will approach the figure 1.6 - this is the norm. The minimum indicator is 0.8, the maximum is 2.5.

If the latter number exceeds the specified one, there is a risk of congenital pathologies. So, Down's syndrome is diagnosed with a TVP of 3.4 mm or more. Its value, exceeding 5.5 mm, indicates Edwards syndrome.

Additional factors affecting the result of ultrasound

Many details are important to obtain accurate results. Among them are:

ultrasound should be carried out strictly during the specified period, and it is most optimal to determine the fetal TVP at 12 weeks;
The KTR of the fetus should be equal to 45-84 mm;
at the time of the ultrasound, the embryo must be positioned correctly: if its head is thrown back, then the TVP will seem larger than it actually is. Conversely, neck flexion reduces the index by approximately 0.4 mm. It is also important that the child be seen from the side - it is from this position that the fold on the fetal neck is best seen;
measurement of TVP should be carried out only along the inner contour of the collar zone;
an important role is played by the image size of the ultrasound device: it is recommended to choose a scale of 2/3 of the ultrasound picture.

In addition to these factors, the qualifications of the ultrasound specialist, as well as the quality of the equipment, are important.

Increased fetal TVP: causes

If during the ultrasound it was found that the amount of fluid in the collar area exceeds the norm, this may be due to such reasons:

problems of the functioning of the heart and blood vessels;
anemia;
infectious diseases;
stagnation of blood in the upper body of the child;
skeletal deformity;
deviations in the formation of connective tissue;
congenital pathologies.

As a rule, the last point is the most common explanation for the fact that the norm of the amount of fluid in the occipital fold is exceeded.

These include anomalies associated with the presence of one extra chromosome in the set - trisomy:

Down syndrome is an anomaly accompanied by deviations from certain medical indicators and impaired physical development of the child.
Patau syndrome is a pathology manifested by underdevelopment of the brain, some internal organs;
Edwards syndrome - along with Down syndrome, it is considered the most common genetic disease associated with deformation of the structure of the skeleton, face, abnormalities in the functioning of internal organs, problems in the overall development of the child.

On the other hand, a missing chromosome, or monosomy, is possible. This phenomenon explains Turner's syndrome, which is observed only in girls and is characterized by a lag in mental and physical development.

When diagnosing one of these pathologies, parents are recommended to terminate the pregnancy, but the decision always remains with them. A child with such genetic abnormalities is a great test for the family, in addition, in many cases there is no guarantee of the baby's survival at all. One way or another, no one has the right to force parents to any decision.

It is also important to understand that the expansion of the collar zone in itself is not an indicator of congenital anomalies: often, in cases where the norm is less than the actual value of TVP, completely healthy children are born. If the TVP norm is exceeded, this is the reason for conducting special examinations that will accurately determine the presence or absence of fetal developmental abnormalities.

The following types of research are assigned:

Repeated ultrasound (fourteen days after the first).
A blood test that will help identify the risks of developmental pathologies.
Examination of amniotic fluid and umbilical cord fluid.

All methods of examination proposed by the doctor should be carried out immediately, since in the presence of anomalies and the decision of the parents to terminate the pregnancy, the duration of the latter is important. The earlier an abortion is done, the less harm it will bring to a woman's health. In addition, the doctor may suggest additional tests to determine the possibility of having healthy children in the future.

Chromosomal anomalies: risk groups

The most common congenital abnormality in the development of a child is Down syndrome, caused by the appearance of an extra chromosome. This phenomenon has nothing to do with gender or race. The main criterion that determines the risk of the syndrome is the age of the father and mother of the unborn child.

The likelihood of an anomaly increases significantly if a pregnant woman is 35 to 45 years old. The opinion about the influence of the age of a man on the birth of a baby with the syndrome is debatable, however, fathers from 42 years old are included in the risk group.

The image of the collar space can be assessed using both transabdominal and transvaginal scanning. Assessment of TVP in the fetus is carried out at values of the coccyx-parietal size (KTR of the fetus) from 45 to 84 mm and allows suspecting chromosomal abnormalities, especially trisomy of the 21st chromosome (Down syndrome) and forming a risk group for the birth of children with congenital and hereditary pathologies among pregnant women .

The thickness of the collar space. Norm

The thickness of the collar space is normally from 0.7 to 2.7 mm depending on the gestational age. The risk of having a child with chromosomal abnormalities increases markedly with the thickening of the collar space and the age of the mother. Therefore, whenever the thickness of the collar space is 3 mm or more, the doctor prescribes an invasive karyotyping (a study that allows you to identify at the cellular level the possibility of having a baby with a genetic syndrome, such as Down syndrome, Edwards, Patau, etc.), using a chorionic villus biopsy (a piece of placental tissue is taken for analysis) or early amniocentesis (in order to obtain a sample of amniotic fluid).

For young women (under 35 years of age) who do not have increased risk factors for chromosomal abnormalities, non-invasive screening ultrasound and blood donation for biochemical markers (PPAP-A, hCG, AFP) may be recommended.

Simultaneous consideration of the mother's age, embryonic TVP and the results of determination of free β-hCG and PAPP-A in the mother's blood serum makes it possible to more accurately confirm or refute the possibility of a child being born with chromosomal abnormalities, as well as to reduce the number of invasive interventions.

Despite the presence of a direct relationship between the frequency of chromosomal defects, congenital malformations and the expansion of the nuchal space in the fetus in the early stages of pregnancy, TVP cannot be fully identified with the need for termination of pregnancy, since healthy children are born in more than 80% of cases. An expanded collar space is only an indication for a more detailed and extended examination, in particular for the timely diagnosis of congenital malformations that may appear later than the detection and disappearance of TVS.