Around the third trimester, when we go to the hospital for our delivery, the doctor will tell us that it’s time for an NT. What exactly is NT? Why do we need NT, when should we have it, and how to read the NT results? Let’s clarify the following questions so that we won’t be unfamiliar with NT anymore. First of all, what is NT? NT (nuchal translucency) refers to the maximum thickness between the skin and the subcutaneous soft tissue in the posterior coronal section of the fetal neck, which is formed by the accumulation of fluid produced by the physiological metabolism of the fetus. During normal embryonic development, the cervical lymphatic vessels and the jugular venous sinus are connected at around 11-14 weeks, before the connection, a small amount of lymphatic fluid accumulates in the neck to form the nuchal translucency layer, which is shown by ultrasound as an echogenic band behind the fetal median sagittal section of the neck (as shown in the figure). Secondly, what is the significance of NT examination? The thickening of the nuchal translucency is closely related to fetal anomalies, and the thickening of the nuchal translucency indicates the possibility of fetal anomalies. The more obvious the nuchal translucency thickening is, the higher the chance of fetal abnormality and the more serious the abnormality is. It has been found that 90% of fetuses with a nuchal translucency of 3 mm are normal and 10% are abnormal, while 90% of fetuses with a nuchal translucency of 6 mm are abnormal. These abnormalities include chromosomal aneuploidy, such as 2l-trisomy, 18-trisomy and x-monosomy (45, X0), in addition to 13-trisomy, 15-trisomy and triploidy; they also include serious abnormalities and rare syndromes of non-chromosomal abnormalities, such as dewlap or anencephaly, cerebral bulge, total forebrain, spina bifida, severe cardiac abnormalities, some diaphragmatic hernia, umbilical bulge, ventral cleft, polycystic kidney, Fetal polycystic kidney, renal agenesis, giant bladder, anomalies of the body clitoris, lethal skeletal malformations and some skeletal muscle anomalies, etc. Thirdly, when to do NT test? The NT test should be done between 11-13+6 weeks of gestation, with a head and hip length between 45-84mm. The best time is 12 weeks, which means that the test is appropriate during your third trimester delivery. To avoid missing the NT test, it is best to have your obstetrician estimate the time for your NT test during your early pregnancy visit, taking into account the ultrasound report.