An NT test for pregnant women is a way to screen for abnormalities in the fetus by ultrasound measurement of the thickness of the posterior hyaline layer of the fetal neck. The test is usually performed at 11-13 weeks + 6 weeks of gestation and its results are more accurate. The technique requires high quality control, and if combined with Down’s syndrome screening, it can further improve the detection rate and reduce the false-positive rate. With the development of non-invasive 4 technology, maternal blood is collected after 12 weeks of pregnancy for prenatal screening of fetal trisomy 21, trisomy 18, trisomy 13 and sex chromosome abnormalities with an accuracy rate of 70%-99%. This technique is called noninvasive prenatal genetic testing, but the test is currently expensive, so it is not yet popular. Alternatively, invasive amniocentesis genetic testing can be taken for more accurate results.