Noninvasive usually refers to noninvasive DNA, and its value is usually as close to 0 as possible, with the closer being an indication of a lower chance of the fetus having the condition.
Non-invasive DNA refers to the risk of a fetus having Trisomy 21 and other chromosomal disorders by drawing peripheral blood from a pregnant woman and testing for fetal free DNA. Noninvasive DNA testing has an extremely high detection rate of over 95% for Trisomy 21, and a relatively high detection rate for Trisomy 18 and Trisomy 13.
A high risk non-invasive DNA test alone does not determine that the fetus has a chromosomal disorder. If the non-invasive DNA test suggests a high risk, an amniocentesis is also required to determine whether the fetus has a chromosomal disorder.
Amniocentesis is the gold standard for diagnosing whether a fetus has a chromosomal disorder. Non-invasive DNA is only a screening method with a higher accuracy rate, and is not a substitute for amniocentesis.