Monday, January 26, 2015
cell free fetal DNA testing
When Amy Seitz got pregnant with her second child last year, she knew that being 35 years old meant there was an increased chance of chromosomal disorders like Down syndrome. She wanted to be screened, and she knew just what kind of screening she wanted — a test that's so new, some women and doctors don't quite realize what they've signed up for.
This kind of test , called cell free fetal DNA testing, uses a simple blood sample from an expectant mother to analyze bits of fetal DNA that have leaked into her bloodstream. It's only been on the market since October of 2011 and is not regulated by the Food and Drug Administration - the FDA does not regulate this type of genetic testing service. Several companies now offer the test, including Sequenom and Illumina. Insurance coverage varies and doctors often only offer this testing to women at higher risk because of things like advanced maternal age.
"I think that I initially heard about it through family and friends," says Seitz. "They had had the option of it given to them by their doctors."
To her, it sounded great. She didn't want an invasive procedure like amniocentesis or chorionic villus sampling (CVS). Those are considered the gold standard for prenatal genetic testing, but doctors must put a needle into the womb to collect cells that contain fetal DNA, which means a small risk of miscarriage.
Studies have shown that the new fetal DNA tests do a better job, says Norton. They're less likely to flag a normal pregnancy as high risk.
"They're much more accurate than current screening tests, but they are not diagnostic tests in the sense that amniocentesis is," says Norton, "and so I think that has led to some confusion."
Even though the newer blood tests do look at fetal DNA, they can't give a definitive answer like an amniocentesis can because they're analyzing scraps of fetal DNA in the mother's blood that are all mixed up with her own DNA.
During amniocentesis, a needle is inserted through a woman's abdomen into the amniotic sac. A sample of fluid is extracted and screened for genetic disorders such as Down syndrome.