Nuchal translucency is a critical test during pregnancy/PR
Nuchal translucency is a very important ultrasound test that is performed from week 11, until week 13 and six more days, through which Down syndrome can be diagnosed in the fetus.
So why is the test so important, and what is increased cervical transparency?
Nuchal translucency is a critical test during pregnancy, which was developed in order to predict Down syndrome and other genetic defects in the fetus.
Before we go into detail and explain about the test itself, including the possibility that we have today, not only to "satisfy" with the transparency test itself, but to "take advantage" of this unique window of time, and significantly expand the scope of the test (to check if there are additional findings), a few words regarding history, related to the diagnosis of Down syndrome.
When was the test developed and why?
In 1866, a British doctor named John Langdon Down described for the first time, a relatively common appearance, which repeats itself among children with a unique facial pattern, short stature and a typical appearance, together with retardation.
And thus, in fact, the syndrome that was also named after him was described for the first time: Down's syndrome.
In 1930, the British Dr. Lionel Penrose noticed that there was a statistical relationship between the mother's age and the degree of risk of Down syndrome. It was only in the 70s of the last century, with the development of genetic diagnosis and the development of the amniocentesis test, that it was decided to allow women Over the age of 36 (in those years), to undergo amniocentesis, funded by the state, in light of a certain increase in risk associated with age. Nevertheless, within a short period of time, it became clear that relying on the woman's age as a single parameter, to detect Down syndrome, does not really provide a diagnostic mechanism effective, since she was able to locate only 25% of the cases.
About three-quarters of the cases appeared precisely in the group of younger women. The explanation for this comes from the simple fact (something that was even more prominent, in the seventies of the last century) that from an absolute point of view, the vast majority of pregnancies in the general population, They are precisely in the younger group of women. Therefore, and in an attempt to improve diagnostic capabilities, in 1984, it was proposed to start using a blood test: the fetal protein (AFP) during pregnancy, to locate these fetuses.
Within a short period of time, two proteins were added to the fetal protein test itself: HCG (pregnancy hormone) and estriol, and these three proteins, combined with the age of the woman, constitute the "fetal protein" test that is known today.
It turns out that this test (a combination of the mother's age, along with the three aforementioned proteins), will succeed in detecting no more than 60% of the cases of Down syndrome, so from everything described above it was clear that we need to continue to strive and look for "something more" that will improve the ability to diagnose in the population of pregnant women and significantly.
In front of her Dr. Erez Yizhar on the "Zap Doctors" website,
the article is courtesy of "Zap Doctors"
In recent years, with the technological improvement in the imaging capabilities and resolution of the ultrasound devices, we are able to diagnose additional findings and abnormalities/PR
The breakthrough in the field
A little over a hundred years will pass, since Dr. Down first described the syndrome in England, and until the beginning of the 90s of the last century, when Professor Nicolaides, also in London, published his impression of "the fullness and thickening of the skin the neck and the back of the neck" in newborns born with Down's syndrome, and then also decided to check whether these signs can already be seen in the ultrasound examinations at the end of the first trimester. In a groundbreaking work published in 1992, he proved that thickening of the nape of the neck in these fetuses already occurs in the ultrasound examination in the first trimester, and that the existence of This thickening significantly increases the risk of Down syndrome, and even other genetic defects. At the same time, he also coined the term "nuchal translucency" for the first time, since the fluid that accumulates in the nape of the neck, during the ultrasound examination, has a "transparent" appearance. Researches Others in other parts of the world, came back and confirmed the discovery, when the data show that a nuchal translucency value of 3 mm or more, between weeks 11-13.6 of pregnancy, significantly increases the risk of Down syndrome and other genetic defects.
It was soon discovered that if we add to the ultrasound examination of the nuchal translucency a blood test and, next to it, the level of two different proteins in the blood: PAPP-A and β-hCG (relevant only in pregnancies with a single fetus), then we can reach diagnostic capabilities approaching 90% From the fetuses with Down's syndrome already at this time of pregnancy (and even before the early examination, and the fetal protein).
So what exactly is the test and what do we test in it?
Nuchal translucency is an ultrasound test in which the distance in the nape of the neck, between the skin and the neck, is measured when the fetus is lying horizontally (laterally), and is not folded: a position that allows the measurement of the fluid level in millimeters, and accurately.
It should be noted that between weeks 11-14 of pregnancy, there is always a certain amount of fluid in this area of the neck, in all fetuses.
This fluid is called lymph, when this phenomenon occurs due to a (normal and temporary) delay in the development of the pipeline that is responsible for absorbing the lymph fluid and which will appear later, so that it will disappear after week 14 (hence also the fixed time limits in which the test can be performed).
As mentioned, many studies have proven a significant statistical relationship between the size of the distance in the nape of the neck between the skin and the neck (amount of accumulated fluid), and the risk of Down syndrome, and other genetic defects.
In the time window described, there will always be a certain amount of fluid in the nape of the neck - even in normal fetuses, but in fetuses with Down syndrome and other genetic defects, according to most, the accumulation of fluid is significantly greater. During the test, the length of the fetus from the head to the rump (CRL) is measured, the thickness of the aforementioned fluid, from the skin to the neck in the nape of the neck, and also look at the existence of the nasal bone (NASAL BONE), when observations have shown that a delay in the appearance of the nasal bone also increases the risk of Down syndrome.
Increased nuchal translucency: so what does this mean?
It is important to understand that even though the transparency of the nape of the neck was planned, originally, fetuses were at increased risk of Down syndrome, it has been proven over the years that increased transparency of the nape of the neck (3 mm or more) also increases the risk of the existence of additional genetic defects (Turner's syndrome, etc.), and even the existence of of other findings - which are not genetic, such as heart defects, infections with various viruses, and other structural defects. At the same time, it is very important to emphasize and point out that increased nuchal translucency in itself does not indicate with absolute certainty whether the fetus is normal or not, but is a screening test. The meaning It is, that in cases where the transparency of the occiput is increased, there is an increase in the risk of the appearance of various defects, and therefore when the transparency is increased, additional things must be done and the tests should be expanded. A careful assessment of the structural integrity of the fetus by a detailed ultrasound review, contacting a genetic counselor, to receive an orderly consultation And the intention is for planning the execution of in-depth tests, such as amniocentesis, fetal echocardiography, blood tests for various viruses, or alternatively making clinical decisions.
"What else" can be diagnosed at this stage?
In recent years, with the technological improvement in the imaging capabilities and resolution of ultrasound devices, we are able , sometimes, the ability to diagnose additional and unusual findings, earlier than we were used to in the past (during the review of the systems) and this by using the advanced ultrasound devices, and sometimes, even in combination with the vaginal transducer.
It should be noted that the actual situation (and complies with the procedures of the Ministry of Health's guidelines) is that not all doctors who perform nuchal transparencies necessarily have the training and knowledge to perform a systems review (requires dedicated and significantly long training).
Hence, the ability, and certainly not always, to arrive at diagnoses of abnormal findings earlier in pregnancy (during the nuchal translucency) requires the combination of: both the use of advanced ultrasound devices, but no less than that - the diagnostic ability of a doctor, who also has the training specific for detecting complex fetal malformations.
From the aforementioned, it appears that although the nuchal translucency test, at least originally, was intended to detect an increase in the risk of Down syndrome, there is the possibility and ability for doctors with the appropriate training (trained to perform a systems review), sometimes, to also see "additional findings", far beyond the risk of Down syndrome, such as Defects of the brain, kidneys, skeleton, urinary system, and more - but subject to the two conditions mentioned: the training ability of the operator and the quality of the ultrasound device.
Here is also the place to emphasize, that there are definitely defects that will not yet appear at this stage, so it is clear that the occipital transparency test, even when it is performed in the most extensive way, does not pretend to or can replace the early review!
An examination that fell short of explaining and emphasizing its great importance.
In fact - today, when a patient comes in for a nuchal translucency examination, a doctor who will investigate and examine in depth, with patience and the time required for this, may sometimes find significant medical findings first - and allow the parents, after receiving the appropriate consultation, to make the most correct medical decision for them, and significantly earlier.
Another important layer, which I come across in my daily life, and many times, during the performance of the nuchal translucency, is to recommend to the parents, when is "the most correct and appropriate" to come for the early examination.
This is because the ultrasound imaging is greatly affected by various factors such as the transgression of the sound waves through the abdominal wall, (very different in different patients), the texture of the abdominal wall, people who have undergone surgeries in the past, and more - something that significantly affects the way the sound waves transgress (a factual limitation of the ultrasound technology: the ability of the sound waves to pass through the tissue) and there is no doubt that we can use the window of time in which the nuchal translucency is optimally performed and recommend to the parents that they come for the early examination (by the way: this is also true for the later examination) - while the ultrasound can produce "the best of the examination" (the best timing - From a technical point of view), it is a fact that those who perform the tests are well aware of its great importance.
As well, we will often come across, during nuchal translucency, that we need to make a correction for the gestational age - something that is easy to do in these early stages, (unlike the tests that will be performed in the second half of the pregnancy).
Correcting the gestational age may also "save a lot of trouble" for the parents later, such as receiving wrong answers (for example: fetal protein that is "supposedly not normal" - due to an error in determining the gestational age, and more).
It is also important to note that the recommendation to perform a nuchal translucency is valid for every pregnant woman, and after we explained the added value of the test, and its many advantages "beyond the issue of the risk of Down syndrome", it is clear that the recommendation to perform a nuchal translucency is absolutely and unequivocally relevant, even for women who intend to have it from the beginning to perform amniocentesis, and for multiple pregnancies, in which a first or second trimester biochemical screening ("fetal protein") is not performed, so that the available detection tests are less in twin or triplet pregnancies, and therefore - the transparency of the nape of the neck is extremely important in these cases as well.
I would like to emphasize a second time - proper back-end transparency is not capable of, nor does it claim to replace, a prior systems review, in a meticulous and rigorous manner, and it seems that the time is short, in this context, to explain its great importance (...requires a separate article), but after we described and explained in detail the importance of The nuchal transparency, I will conclude by saying that it is important to take advantage of an important window of time, and to try to reach the best and broadest possible diagnosis, beyond the nuchal transparency itself, for the benefit of the parents - although this definitely requires an investment of time,
Dr. Yizhar Erez. Senior physician in the gynecological ultrasound unit at Lis Hospital (Ichilov).
Kaplansky 15, Givataim.
050-2220965
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