In recent years, noninvasive prenatal screening tests have been made available. These tests involve blood being taken from the expectant mother as early as 10 weeks of gestation. It relies on the detection of cell-free DNA that circulates between the fetus and the expectant mother. According to the latest research, this blood test can detect up to 98.6% of fetuses with trisomy 21. A “positive” result on the test means that there is a 98.6% chance that the fetus has trisomy 21; a “negative” result on the test means that there is a 99.8% chance that the fetus does not have trisomy 21. The turn around time for the test is about 8-10 days, and approximately 0.8% of the time, results are not obtained from the tests due to technical standards. While the initial clinical trials were conducted just on cases with trisomy 21, one form of Down syndrome, a “positive” result cannot distinguish between trisomy 21, translocation Down syndrome and high-percentage mosaic Down syndrome. Put another way, a “positive” result will pick up all forms of Down syndrome, except mosaic Down syndrome that is 33% or lower. All mothers who receive a “positive” result on this test are encouraged to confirm the diagnosis with one of the diagnostic procedures described in the link below. (source:NDSS.org)

 

https://www.ndss.org/resources/understanding-a-diagnosis-of-down-syndrome/