NF is a screening test for Down’s syndrome, a prenatal test that measures the thickness of the fetal nuchal fold with color ultrasound in the middle of pregnancy, usually performed at 15-20 weeks of gestation, to determine the presence of chromosomal abnormalities in the fetus. The most common disorders such as trisomy 21, or Down’s syndrome, may manifest as obvious congenital mental retardation, peculiar facial features, mental and physical developmental delays, digestive tract abnormalities, and heart disease in affected children. However, there will be a few fetuses with normal karyotype of NF thickening, such as fetuses with congenital heart malformation, which may experience temporary heart failure, resulting in elevated venous pressure and impaired lymphatic return, allowing excessive lymphatic fluid to accumulate in the fetal neck and presenting as NF thickening. It is important to maintain a good state of mind before the NF examination. Generally, no special preparation is needed, and regular feeding is sufficient, and there is no need to hold urine. If NF thickening is detected during NF examination, it can be combined with maternal age, maternal history, pregnancy medication and other medical history as well as serum markers to comprehensively analyze the risk of fetus with trisomy 21, and if necessary, amniocentesis amniotic fluid cell culture can be performed to determine the diagnosis.