Use of cell-free DNA for secondary screening for Down syndrome

Pregnant women can choose to have a blood (serum-based) screening test to find out whether they have a high or low risk of having a baby with Down syndrome. The blood test has been offered for many years. Most women find they have a low risk and continue with routine care. In some women, the blood test will find a high risk. These women can find out for sure if the baby has Down syndrome by having an invasive test like amniocentesis. There is now a new option for the women at high risk (shaded box and dashed arrows): a new blood test that looks at the baby's cell-free DNA that is in the mother's blood and again determines if she is high or low risk. Most women find they have a low risk and continue with routine care. A few women will have a high risk (50 percent or more) on the DNA test, and the DNA test does not work (test failure 1 to 5 percent) for some others. These women would still need an invasive test to know for certain if the baby has Down syndrome.