Trisomy 21 is generally referred to as Down’s syndrome, and the critical risk of 1:539 is a reference ratio for Down’s screening, which is risky but not absolute. There is a risk, but not an absolute risk. Down’s syndrome screening itself has a certain false-positive rate, and the Down’s syndrome screening value is only a reference ratio value.
If the Down’s syndrome screening index exceeds the normal value, non-invasive DNA screening or amniocentesis test should be performed. If the test is normal, Down syndrome can be maximally excluded. Down’s syndrome screening can only determine the chances of a fetus having Down’s syndrome, not whether the fetus has Down’s syndrome.
Even low-risk people cannot completely rule out Down syndrome, so the critical risk requires further testing. If there are no abnormalities, there is nothing to worry about.
If there is an abnormal Down’s syndrome screening result, there is no need to be too anxious. A single piece of test data tells you nothing. It is recommended to follow the doctor’s instructions for further examination, to clarify the cause with the help of the doctor, and to carry out targeted treatment.