The NT test result is normal, which only indicates a low risk of fetal chromosomal abnormalities, but the need for non-invasive DNA testing is determined by the risk of Down’s syndrome, the family history of the pregnant woman, her age and other factors. The NT test is more accurate than the NT test in that it can be used to determine whether the fetus has chromosomal abnormalities and congenital genetic problems based on the maternal weight and gestational week, and can accurately rule out trisomy 21, trisomy 13 and trisomy 18. If a family history of chromosomal disorders is not present and the mother is <35 years old, non-invasive DNA testing is usually not necessary. If the pregnant woman has a family history or is >35 years old, a repeat 4D ultrasound and Down’s syndrome screening is recommended at 16-20 weeks of pregnancy. If the Down’s syndrome screening is low risk, non-invasive DNA testing is usually not necessary. If the Down’s syndrome screening has gray area manifestation or high risk, only then will it be recommended to go for non-invasive DNA testing.