Fetal Arrhythmia - A Pediatric Cardiologist's Perspective | Webinar | Dr S Mani Ram Krishna | AIMS
Fetal TVP by week: table of normal values
When carrying a fetus, a woman has to undergo many medical examinations. One of these is fetal TBP. The term is deciphered by the phrase the thickness of the collar space is the amount of fluid accumulating on the neck of the fetus 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 of its development due to changes in DNA. Usually, such violations are detected immediately by the mother's body itself - then miscarriages occur.
If the abnormalities appear at a later date, babies survive, but are born with various genetic diseases. That is why the definition of TBP of the fetus at 12 weeks is an important moment 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 within a strictly defined period.
This is due to the following reasons:
- The area at the nape of the embryo increases by week, starting from the 10th. Until then, 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 meaningless.
Measurement of the size of the cervical fold of the fetus is performed by ultrasound. The pregnant woman is placed on a couch with her back facing down. The ultrasound machine has a special probe that is lubricated with a conduction-enhancing gel.
There are two methods of performing ultrasound:
- Transabdominal, in which the transducer of the ultrasound machine is located outside: the doctor guides it over the abdominal region, having previously lubricated the woman's belly with gel.
- The transvaginal method is suitable for situations where it is difficult to determine the location of the fetus. Then the sensor, with the condom put on it and the applied gel, is immersed in the vagina.
Having received the necessary data, the doctor compares the indicators of fetal TBP by week.
Table of RTA by week
|Period||Average value of TVP norm, millimeters||Normal limits, millimeters|
|10 weeks||1.5||0.8 - 2.2|
|11 weeks||1.6||0.8 - 2.4|
|12 weeks||1.6||0.8 - 2.5|
|13 weeks||1.7||0.8 - 2.7|
|14 weeks||1.8||0.8 - 2.8|
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 method.
What does the weekly rate table show? As an example, you can analyze the RST data for the 12th week. For women expecting a healthy child, the value of the collar zone will approach 1.6 - this is the norm. The minimum is 0.8, the maximum is 2.5.
If the last number exceeds the specified, there is a risk of congenital abnormalities. So, Down syndrome is diagnosed with a TVP index of 3.4 mm or more. Its value exceeding 5.5 mm indicates Edwards syndrome.
Additional factors affecting the ultrasound result
Many details are important to get accurate results. Among them are:
- an ultrasound scan should be carried out strictly within the specified period, and it is most optimal to determine the TVP of the fetus at 12 weeks;
- CTE of the fetus should be 45-84 mm;
- at the time of the ultrasound, the embryo must be located correctly: if its head is thrown back, the TVP will seem larger than it really is. Conversely, flexion of the neck decreases the reading by approximately 0.4 mm. It is also important that the baby is seen from the side - it is from this position that the fold on the neck of the fetus is best seen;
- TVP measurement should be carried out only along the inner contour of the collar zone;
- The image size of the ultrasound device plays an important role: it is recommended to select a scale 2/3 of the ultrasound image.
In addition to these factors, the qualifications of the ultrasound specialist, as well as the quality of the equipment, are important.
Increased Fetal TST: Causes
If during an ultrasound scan it was found that the amount of fluid in the collar area exceeds the norm, this may be due to the following reasons:
- problems with the functioning of the heart and blood vessels;
- infectious diseases;
- stagnation of blood in the upper part of the child's body;
- skeleton deformation;
- abnormalities in the formation of connective tissue;
- congenital pathologies.
As a rule, the afterbirthny point is the most common explanation for exceeding the amount of fluid in the occipital fold.
This includes 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's syndrome is considered the most common genetic disease associated with deformation of the skeleton, face, abnormalities in the work of internal organs, problems of the general development of the child.
On the other hand, there may be a lack of a chromosome, or monosomy. This phenomenon explains Turner 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 big 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 make 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 real value of TVP, completely healthy children are born. If the TVP rate is exceeded, this is a reason for conducting special examinations, which will accurately determine the presence or absence of fetal developmental abnormalities.
Assign the following types of research:
- Repeated ultrasound scan (fourteen days after the first).
- A blood test that will help identify the risks of developmental pathologies.
- Study of amniotic fluid and umbilical cord fluid.
All the examination methods 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 term of the latter is important. The sooner an abortion is performed, 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 abnormalities: risk groups
The most common congenital developmental disorder of a child is Down syndrome, caused by 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 between 35 and 45 years old. The opinion about the influence of a man's age on the birth of a baby with the syndrome is controversial, but the risk group includes aboutttsov from 42 years old.
Also, the likelihood of developing a fetus with abnormalities is high in families with blood relatives with chromosomal abnormalities. Heredity is a factor whose presence significantly increases the risk of the syndrome, so if such cases have already been noted in the family, the doctor will advise not to plan a pregnancy at all.
When comparing the obtained results of ultrasound of TVP with the table where the norm is indicated, the doctor takes into account other circumstances that can affect the development of the fetus. If there is a slight deviation from the figure, which is marked as normal, but there are no other risk factors, then, most likely, additional analyzes will show the absence of pathologies. On the other hand, if, when the thickness of the collar region is exceeded, the parents are in the specified age category, or there are already relatives with the syndrome, the likelihood of having a child with congenital abnormalities is high.
In the first three months of pregnancy, the most important study of the fetus is precisely ultrasound, which determines the size of the child's cervical zone. An increase in TBP in a fetus does not mean a deviation of its development. There may be other reasons for this indicator, mentioned above.
But you cannot ignore the figure exceeding the norm - it is always better to play it safe and take additional tests to make sure that the baby is born healthy.