Normal NT value is not necessarily normal chromosome, but also combined with non-invasive prenatal testing technology or prenatal diagnosis and other tests to clarify. NT refers to the thickness of fetal nuchal translucency, which is an ultrasound examination for screening the risk of chromosomal disorders in fetus during early pregnancy, and the normal value should be <2.5mm, when the NT examination is normal, it does not determine whether the chromosomes are normal. A mid-pregnancy serologic screening test or amniocentesis should also be performed to confirm chromosomal abnormality. For low-risk individuals, Down's syndrome screening is required, and for those at critical risk for Down's syndrome, non-invasive prenatal screening techniques can be performed to rule out fetal abnormalities, but prenatal diagnosis is recommended for high-risk individuals to determine fetal chromosomal abnormality. For those with intermediate to high risk, non-invasive prenatal screening technology or prenatal diagnosis should be performed as prescribed by the doctor. Consult your doctor for advice.