NT examination is performed at 11-13 weeks + 6 days of gestation to check the thickness of the nuchal translucency, which is too small to be imaged before 11 weeks, and disappears after 14 weeks of gestation. If the week of pregnancy is more than 12 weeks but less than 13 weeks + 6 days, an NT result of <3.0mm is normal. If the NT value exceeds the normal range, you can consult your doctor to decide whether to undergo further diagnostic tests such as non-invasive prenatal genetic testing or amniocentesis. If the thickness has reached 6mm, the risk of the fetus having Down syndrome and other chromosomal abnormality diseases and heart problems is high, and further amniocentesis or chorionic villus biopsy is needed to clarify the situation. While undergoing the NT test, the head and hip length of the fetus will be measured to determine the gestational week, and the amniotic fluid, placenta, uterus, and adnexa will also be observed, as well as the structures of the fetus, such as cranial, nasal, facial, spinal, and cardiac development, to rule out major malformations.