NT thickening of 4.5 has a relatively high probability of malformation, but there is no specific percentage. An NT thickening of 4.5 mm does not indicate that the pregnancy needs to be terminated immediately or that the fetus is definitely chromosomally abnormal.The NT value, i.e. the thickness of the posterior nuchal translucency zone of the fetus, needs to be examined at a specific range of gestational weeks. If the fetal NT is thickened, the baby’s gestational week needs to be checked to see if the NT was measured during 11-13 weeks + 6 days of pregnancy; if it is greater than this, the NT is likely to be elevated. The normal value of NT is ≤2.5mm, if it is larger than this value, it is not clear that the fetus is definitely malformed, but the probability of having chromosomal abnormality is increased, and further examination is needed, such as non-invasive DNA test or amniocentesis, both of which can help diagnose the presence of chromosomal abnormality in the fetus. Moreover, the NT measured by different ultrasound doctors varies to a certain extent, if the NT value is reported to be 4.5mm thickened in the screening hospital, the NT should be rechecked in the prenatal diagnostic hospital, and if the rechecked NT is still abnormal and still shows thickening, amniocentesis or non-invasive DNA testing should be done to clarify.