NT and Down’s syndrome screening are both methods of screening Down’s syndrome children, but the two examination methods and examination time are not the same: 1, examination method: NT is through ultrasound examination, while Down’s syndrome screening is through blood sampling. The risk factor of fetal trisomy 18, trisomy 21 and neural tube defects can be determined by taking the blood of pregnant women and testing their serum concentrations of alpha-fetoprotein, HCG and free estriol, combined with maternal age, weight and gestational age; 2. Screening test is usually performed at 15-20 weeks + 6 days of pregnancy. NT and Down’s syndrome screening can both assess the risk of fetal chromosomal abnormalities, and early Down’s syndrome screening can combine the two to effectively improve the screening rate of fetal chromosomal abnormalities.