Usually, NT thickening in one of the twin fetuses means that in one of the twin children, the thickness of the fetal nuchal translucency exceeds the normal value, which needs to be alerted to the associated diseases caused by chromosomal and genetic abnormalities. NT is a strong marker of aneuploidy and is normal within 3 mm, greater than 3 mm, 90% are normal fetuses, 10% are abnormal fetuses, and greater than 6 mm, 90% are abnormal fetuses. If the NT is thickened, further non-invasive prenatal screening or prenatal diagnosis is needed to rule out fetal chromosomal abnormalities. If the fetal posterior nuchal translucency is found to be thicker than normal, genetic counseling and prenatal diagnosis should be conducted under the guidance of a doctor. Fetal karyotyping, such as non-invasive DNA testing, chorionic villus aspiration or amniocentesis, is recommended.