Noninvasive Prenatal testing

Cell Free Fetal DNA

By now if you are pregnant or considering it in the near future I am sure you have done some online “research”. And if this assumption is accurate, then it is also likely that you have surely noticed the introduction of the newest prenatal testing available, noninvasive prenatal screening, Cell Free Fetal DNA Testing. So hopefully this information will clarify what it is, who it is available to, and help give a little guidance on your personal choice of whether to include this testing in your prenatal care or not.

So what is “Noninvasive Prenatal Testing”? Well, we have been offering prenatal screening for decades, this includes the Quad screen that was offered at 16-19weeks gestation, and in more recent history the First Trimester Screening, which is a blood test as well as an ultrasound to assess nuchal translucency. These screening tests were used to assess a patient’s risk of having a pregnancy affected by a chromosomal abnormality, specifically screening for Trisomy 21 (Down Syndrome), Trisomy 13, and Trisomy 18. General risk assessment is based on the maternal age. The older the woman is when she achieves pregnancy, the higher the risk of chromosomal anomalies, as well as other complications. Now, in all honesty these tests do offer a little different screening then the older tests. The Quad screen includes testing for neural tube defects as part of its panel. This is not part of the cell free fetal DNA testing. The Quad screening works by checking 4 different hormones in the maternal blood, alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), inhibin A, and estriol (uE3). Based on which hormone was elevated and which was low they were able to assess a risk for the chance of fetal chromosomal problems. I stress a “risk”, as there was not any fetal information that was obtained or tested. Based on the risk your provider would then discuss additional diagnostic testing, or amniocentesis if desired, or reassure you that your chance of a baby with a chromosomal abnormality was decreased. The First Trimester Screening became available more recently and in addition to the maternal hormones tested as above there is also a transvaginal ultrasound that assessed the nuchal translucency (measured the back of the fetal neck). There was a calculation done with the information collected and the results that were given were much more sensitive than the Quad screen alone. An additional benefit to the first trimester testing was that it was offered earlier in the pregnancy. The diagnostic testing that is offered with abnormal test results is invasive, either chorionic villus sampling (collecting placental tissue in the first trimester) or amniocentesis (collecting amniotic fluid after the second trimester). Both of these tests carry with them a risk of miscarriage.

Now back to the question of Noninvasive Prenatal Testing. It has been known that fetal cells can be found in maternal circulation. But more recently investigations have been done to collect a specific part of this information, the nucleic acids, DNA without a cell membrane. That we can find this in the maternal blood stream at times in a substantial quantity has potential for prenatal diagnosis of fetal DNA. This fetal information can be detected in mom’s blood stream as early as 5 weeks, and more often by 9weeks. Thus the testing is offered at 10 weeks. Currently the test is targeted at finding elevated levels of chromosome 21 (Down Syndrome), 13, and 18. This method of testing is much more sensitive than our previous tests that were discussed above. Studies have shown this test to be >99% for Trisomy 18 and 21 and over 80% for Trisomy 13 (specificity). In addition this test screens for sex chromosome abnormalities, which occur in nearly 1 in 400 births. A perk is finding out the sex of your baby as early as 10 weeks with nearly 98% accuracy.

The most recent issue of the Green Journal, which is the medical journal of the American College of Obstetrics and Gynecology, has an original research article addressing this testing. What this means is that there is now better medical evidence to support offering this testing to the general, or low risk population.

I often explain to my own patients that just because we are scientifically able to find out more and more information about our unborn babies, it does not mean screening is the right thing to do for each family. Deciding whether or not to do noninvasive prenatal testing is a very personal decision and our goal as healthcare providers to make sure you get that information and answer your questions.

Noninvasive prenatal screening is available through your prenatal care provider. Hopefully this information is useful as you set out to have a healthy, well informed pregnancy. If there is anything we at Omaha Ob Gyn can do to assist you and your family in that goal please call. We would love to!


References: Uptodate.com