Amnio vs. Genetic Blood Testing: August 3, 2013

Each year about 200,000 women undergo amniocentesis to look for genetic abnormalities in their unborn child. While the procedure is safe, it is an invasive test for mom and comes with a slightly higher risk of miscarriage.

“An amniocentesis is done under ultrasound guidance and basically there’s a small needle we put through the abdomen of the mom, into the amniotic sac, and we draw some fluid out of the sac and send that for evaluation,” says Dr. Melissa Lee, obstetrician with Lee Memorial Health System.

Usually done in the first trimester, amniocentesis assesses genetic defects, along with lung maturity, infection and other issues including RH compatibility.

“And that is considered definitive testing, not only for trisomy 18, 21 or 13 but also for other genetic syndromes, that we can’t test with the MaterniT21,” says Dr. Lee.

Some doctors and moms are opting for a newer blood test, one called MaterniT21 that can be given earlier in pregnancy, without the stomach stick.

“That’s actually a blood draw from the mom. Anytime after 10 weeks of gestation. What it’s looking for is DNA of fetal origin in the maternal circulation. And that’s how we can draw it from the maternal blood and send it for evaluation,” says Dr. Lee.

Needleless yes, but there are some sticking points. The blood test only evaluates three genetic sequences, ranging from an extremely precise view of Trisomy 21, which is Down’s Syndrome, to a less accurate read on Trisomy 13.

“There always is the option later if the MaterniT21 comes back abnormal, of proceeding with an invasive test to kind of confirm anything from there,” says Dr. Lee.

MaterniT21 is still in its infancy, but many women with high-risk pregnancies are happy for its arrival.