Modern prenatal diagnostics allows not only to establish the sex of the child long before his birth, but also helps to identify possible malformations, most of which become visible during ultrasound examination. One of the important indicators detected at the first ultrasound screening is the size of the collar zone of the fetus.
First trimester screening
First trimester screening is done between the 11th and 14th weeks of fetal development. In this case, the doctor pays special attention to the so-called collar zone, the size of which is determined by the amount of accumulated lymphatic fluid in the occipital region of the fetus. An increase in its amount may signal the presence of a possible genetic defect, for example, trisomy 21, which is the cause of Down's syndrome.
Collar size
The size of the collar zone depends on the age of the fetus. At the beginning of the 11th week, a value of up to 2 mm is considered normal, by the end of the 13th week it can reach 2.8 mm. At the same time, do not panic if the numbers turn out to be slightly overestimated. According to statistics, 9 out of 10 babies with a collar zone size between 2, 5 and 3.5 mm are born completely healthy. And only when the indicator turns out to be significantly overestimated, for example, 5-6 mm or more, one can suspect the presence of a genetic defect. After the 13th week, the fetal lymphatic system is formed, the fluid from the collar zone spreads through the vessels of the body, and the measurement indicators are no longer relevant.
Additional research
Moreover, it should be understood that these indicators, although they are considered a rather important point in prenatal diagnosis, are not a diagnosis in themselves. This is just a screening that helps to assess the degree of risk of a particular disease. Therefore, no doctor has the right, relying only on a high value of the size of the collar zone, to send a woman for an abortion. Accumulation of lymphatic fluid in the neck does not necessarily mean that the baby has some kind of genetic defect. On the other hand, no one can guarantee that a fetus with a normal collar area will be born completely healthy. Therefore, other studies may be necessary. For example, cordocentesis or analysis of amniotic fluid, which allows you to give more specific data about the health of the baby.
Measurement error
In addition, do not forget about the probability of measurement error. The fetus is still so small and it is quite difficult to measure it down to a tenth of a millimeter. And the device may be old, and the doctor is not yet so experienced, and the position of the fetus is not the most optimal, therefore, if dubious results were obtained during the first trimester screening, it is always worth rechecking them with another specialist and on other equipment.
