The NT thickening of 3mm is necessary for review, the NT thickening may indicate the risk of chromosomal abnormalities in the fetus, and further examination is necessary. NT examination mainly refers to the measurement of fetal nuchal translucency thickness by ultrasound to screen for the risk of chromosomal abnormality in the fetus, clinically the normal range of NT value is less than 2.5mm, when the NT result is 3mm, it is an abnormal result, and it is necessary to carry out further non-invasive DNA or amniocentesis under the guidance of the doctor, to rule out the risk of chromosomal abnormality in the fetus. NT examination is mainly carried out by ultrasound, the examination time is generally 11~13+6 weeks of pregnancy, it is recommended that pregnant women try their best to do regular obstetric examination during pregnancy, to avoid missing the obstetric examination program resulting in adverse consequences.