Cervical hyaline layer is an abbreviation for the translucent membrane of the fetal neck, a translucent protein membrane that surrounds the mobility of the posterior part of the fetal neck around 10 to 13 gestations. Its thickness is related to certain fetal defects and can be measured by ultrasound imaging. Fetal nuchal translucent tissue thickness is the thickness between the dorsal soft tissues and the skin of the fetus and is considered to be the most effective indicator for screening fetuses with Down syndrome because children with Down syndrome tend to have soft tissue edema in the neck, whereas normal fetuses do not have this abnormal sign. It is thought that the cause of thickened fetal nuchal translucent tissue may be related to cardiovascular anomalies due to chromosomal abnormalities and early cardiac failure due to severe cardiac anomalies such as ventricular septal defect and aortic stenosis, while cephalic and cervical vascular and lymphatic vessels are underdeveloped; it has also been reported that if a fetus shows abnormal fetal nuchal translucent tissue thickness in early pregnancy, its development of Down’s syndrome or other trisomy It has been reported that the chance of Down’s syndrome or other trisomic syndromes is 13 times higher if the fetus shows abnormal nuchal translucency in early pregnancy, and it has diagnostic significance from 10 to 22 weeks of gestation, but the diagnostic value is highest from 10 to 14 weeks. In early pregnancy, the term “translucency” is used irrespective of whether the fluid collection at the back of the neck is next door or confined to the neck. In midtrimester, the translucency usually subsides, but in a few cases, it may become cervical edema or hydroceles. Cervical translucency – measurement should be performed at 11-13+6 weeks when the fetal head-rump length is 45-84 mm. A median sagittal view of the fetus should be obtained and the NT should be measured in the natural fetal position. the image should always be maximized so that it shows only the head and upper thorax. The fetal skin and amniotic membrane should be carefully distinguished by measuring in the clear zone with the widest distance between the skin and the soft tissues on the cervical spine. Measurements should be taken more than once during the scan, and the maximum value obtained should be recorded. In normal fetuses, NT thickness increases with fetal head-rump length. The median and 95th percentile NT thicknesses are 1.2 and 2.1 mm, respectively, at a head-rump length of 45 mm and 1.9 and 2.7 mm, respectively, at a head-rump length of 84 mm. However, the 99th percentile does not vary significantly with head-rump length, being approximately 3.5 mm. NT thickening is defined as a thickness exceeding the 95th percentile, regardless of whether the hydrops is compartmentalized, localized or generalized. After 14 weeks, NT thickening usually subsides, but in some cases it evolves into cervical edema or hydrocysticercosis. Fetal NT thickening at 11C13+6 weeks is a common sign of chromosomal abnormalities, multiple fetal malformations and genetic syndromes. The prevalence of fetal pathology and adverse pregnancy outcomes increases exponentially with increasing NT thickness. However, if the fetal NT is between the 95th and 99th percentiles, the chance of delivering a baby without severe pathology is over 90%; if the NT is between 3.5 and 4.4 mm, it is about 70%, between 4.5 and 5.4 mm, between 5.5 and 6.4 mm, 30%, and above 6.5 mm, 15%. The vast majority of fetal lesions associated with NT thickening are diagnosed in a series of tests performed before 14 weeks of gestation.