What is the difference between noninvasive prenatal genetic testing and Down's screening?

What is the difference between noninvasive prenatal genetic testing and Down's screening? Noninvasive prenatal genetic testing and Down screening are mainly used to prevent prenatal testing of Down syndrome.
Down syndrome is the most common disease leading to mental retardation and the most common disease caused by genetic material defects, with an overall incidence rate of about 1/700.
more importantly, the occurrence of Down syndrome is completely random, and every pregnant woman is at risk of having a child with Down syndrome.
, therefore, whether it is noninvasive prenatal genetic testing or Down's screening, their suitable population is normal pregnancy pregnant women.
Down screening is by far the most widely used prenatal screening for Down syndrome.
it is characterized by its simple operation, cheap price, and a long period of accumulation of clinical practice. The main problem with
Down screening is the relatively high rate of misse and very low specificity.
the detection rate of Down's screening is about 30%, while the specificity of Down's syndrome is about 1% to 2%.
noninvasive prenatal genetic testing is designed for the same purpose as Down screening, and is a screening method used primarily to prevent Down's syndrome.
but noninvasive prenatal genetic testing is better than Down's screening in terms of accuracy.
noninvasive prenatal genetic testing had a leakage rate of only about 2% on Down's syndrome, while specificity reached about 99%.
noninvasive prenatal genetic testing is a method far superior to Down's screening in terms of accuracy.
compared to Down screening, its main drawback is that it is more expensive, and clinical application time is short, long-term effects need to be observed.
make a specific hypothesis about the difference between noninvasive prenatal genetic testing and Down's screening.
assuming that Down screening has a 70% detection rate for Down syndrome, and if you are screened for Down's, your child's chances of having Down's syndrome will be reduced from 1/700 to 1/2333, or 1/3.3.
that's what Down screening means.
for noninvasive prenatal genetic testing, assuming a detection rate of about 99% for Down syndrome, if you have a noninvasive prenatal genetic test and the results show that it is normal, your child's probability of having Down syndrome will be reduced from 1/7000 to 1/70000, i.e. to 1/100.
this is the advantage of noninvasive prenatal genetic testing for Down's screening rate.
99 out of every 100 fetuses with Down syndrome, compared with about 70 for Down screening.
if specificity is taken into account, the specificity of noninvasive prenatal genetic testing is more than 99%, i.e. 99 of the 100 noninvasive prenatal gene tests determined to be at high risk of down syndrome.
and Down screening is about 1% to 2%, meaning that only 1-2 out of every 100 Down screening-rated pregnant women who are considered to be at high risk do have Down syndrome.
, as a result, Down's screening will result in a large number of false positives compared to noninvasive prenatal genetic testing, and the psychological burden of these pregnant women and the actual risk of amniotic fluid punctures are considerable.
If analyzed purely technically, noninvasive prenatal genetic testing is clearly a highly accurate screening method suitable for replacing Down's screening.
recommends that pregnant women with financial conditions use noninvasive prenatal genetic testing instead of Down's screening.
Source: Decoding Medicine.