1.What is NT? In this article, we talk about NT not to discuss New Technoly, New Taiwan Dollar, or the sensitive National Treatment, but the Nuchal Translucency, which is the maximum thickness of the soft tissue between the skin layer and the fascial layer at the back of the fetal neck. The thickness of NT is also the maximum thickness of the soft tissue between the skin layer and the fascial layer at the back of the fetal neck. 2. How is NT formed? Before the normal embryonic lymphatic system is complete, a small amount of lymphatic fluid collects in the cervical lymphatic sacs or lymphatic vessels, forming the nuchal translucency layer. After 14 weeks, when the lymphatic system is well developed, the accumulated lymphatic fluid rapidly drains to the internal jugular vein, and the nuchal translucency layer then disappears rapidly. Whether due to genetics, anatomy or infection, the delayed communication between the lymphatic vessels and the jugular vein may cause obstruction of lymphatic return, resulting in excessive accumulation of lymphatic fluid in the jugular region, which leads to the thickening of the hyaline layer and even the development of cystic lymphadenoma (lymphatic hydrocystic tumor) in the middle of pregnancy. 3.What is the significance of NT? More often than not, it is the obstetrician who asks us to measure NT thickness by ultrasound, the specific significance of which is very long, in short, NT is closely related to chromosomal abnormalities, including trisomy 21, trisomy 18, trisomy 13, etc. Increased NT is also associated with serious abnormalities and rare syndromes that are not chromosomal, such as congenital heart disease, non-immune edema, cervical early stage of cystic lymphadenoma, etc. However, it should be noted that about 80% to 90% of NT abnormalities in fetuses are transient lesions with normal final results. If thickening of the hyaline layer is detected, in addition to the recommended fetal karyotype check, close follow-up is needed for those with normal karyotype to rule out congenital heart development abnormalities. 4.How is NT measured? This part is the focus of our ultrasound attention. The following text and pictures in bold are from the Chinese textbook of FMF Foundation. (1) It should be performed at 11-13+6 weeks, when the fetal head and rump length is 45-84 mm. If your obstetrician asks you to measure the NT of a fetus at 20 weeks of gestation, you can rightfully refuse and despise it. (2) Obtain a mid-sagittal view of the fetus and measure the NT in the natural position; if the fetus is too nervous, you can reassure it with the “fetal language” that the ultrasound is harmless and that the baby is relaxed. (3) Always zoom in on the ultrasound image so that only the head and upper chest are visible. The fetus is the main character and you should let him or her occupy at least 3/4 of the whole screen. (4) Measurements should be taken in the clear zone at the widest distance between the skin and the soft tissue on the cervical spine. This statement is meant to remind you not to take the bull by the horns, the open area is the best target for you to chase. (5) Be careful to distinguish between fetal skin and amniotic membrane. Sometimes what you think is simple is often easier to miss. Patting the PP of the fetus and making him move around may be enough to identify it. (6) The transverse vernier ruler should not be placed on the cervical fluid, but on the border of the white line until the two are fused and the transverse ruler is not easily visible. As the “judge” of the scale, should have Chinese characteristics, and never interfere with the internal affairs of other countries. (7) In the scan, the number of measurements should be more than once, and record the maximum value of the measurement obtained. Don’t be middle of the road, don’t be evenly divided, and demand the maximum benefit. (8) When the fetus’ neck is surrounded by the umbilical cord, its NT thickness should be measured above and below the umbilical cord, taking the average of the two values. The fetus is actually very well behaved, you wait for him for half an hour or he will not be in a mood. (9) The ultrasound instrument used must have a high resolution, image playback function that provides a light scale accurate to 0.1 mm measurement. You can take this WeChat message and find the dean’s theory as a bird’s eye view. The following six images are all fetal sonograms at 12 weeks of gestation, all of which achieved good midsagittal views of the fetus. Figure (a) is suitable for measuring NT because it shows only the fetal head and upper thorax, and a thin transparent layer separated from the amniotic membrane is visible. In Figure (a) Figure (b), the image is not sufficiently magnified to meet the picture standard of the Wuda head saga for accurate measurement of NT. In Figure (b) Figure (c), the fetal neck is hyperextended for accurate measurement of NT. In Figure (c) Figure (d), the fetal neck is (d) In figure (e), the maximum thickness of NT should be measured. In Figure (e) and Figure (f), because the neck is surrounded by the umbilical cord, the NT should be measured at both the upper and lower parts of the umbilical cord, and then the average of the two should be used to calculate the risk. Figure (f) 5. What are the criteria for determining NT? The commonly used judgment index is NT ≥ 2.5 mm at 10-14 weeks of gestation, which is considered abnormal. However, the judgment of NT abnormality should not only be combined with the gestational week, but also consider the age of the pregnant woman, and the range of abnormal value should be relaxed if the pregnant woman is of advanced age (above 35 years old).