Prenatal Testing: Part 2
Non-Invasive Prenatal Screening (NIPS)
MaterniT21, Verifi, Harmony and Panorama represent some of the latest developments in prenatal testing with their use of cell free DNA (cfDNA) analysis. These tests analyze the mother’s blood along with the placental material that has entered the mother’s bloodstream for genetic abnormalities, such as Trisomy 21 (Down Syndrome) and Trisomy 18 (Edwards syndrome). While these are the most advanced and accurate non-invasive screenings on the market, there are two very important things to note: 1) these tests analyze placental material, not fetal material. While the two are usually the same in terms of genetic material, this is not always the case. 2) These tests can be very expensive, upwards of $1000, and may or may not be covered by insurance depending on a mother’s determined risk. (Some companies do advertise price adjustments if insurance will not cover a test, but this is something that is typically determined on an individual basis and should be explored before taking the test.)
Parents should keep in mind that the accuracy for detecting a problem is not the same as a test’s positive predictive value (PPV), which is the number of “screen positive” tests that were later determined to be “true positives.” A test can be considered 99% “accurate” if it identifies 99% of genetic problems (this is referred to as the test’s sensitivity); however, the same test may also return “false positives,” which would lower its PPV. Because these tests, particularly in low-risk populations, still return false positives as well as false negatives, they are labeled as “screenings” rather than “diagnostic” tests. In other words, if there is a genetic problem, the test will identify it 99% of the time, but may also return a positive result for a problem when there isn’t one. This can cause a lot of unnecessary distress.
CVS (chorionic villus sampling) and Amniocentesis
CVS and Amniocentesis are both invasive diagnostic tests. CVS testing uses placental cells (similar to cell free DNA testing) typically gathered with a catheter or needle inserted through the vagina and cervix that removes cells from the placenta. It is done during the first trimester of pregnancy. An amniocentesis, performed any time after 15 weeks of pregnancy, gathers shed fetal cells from within the amniotic fluid by inserting a needle into the mother’s abdomen. Some may consider the difference in material tested a small distinction; however, it’s important to consider all the information when weighing the pros and cons of an invasive test, especially since both CVS and Amniocentesis carry a small risk of miscarriage. Be sure to evaluate your particular risk factors by talking with knowledgeable and supportive people in your life (such as family, close friends and/or your doula) as well as your care provider to make the best decision for you and your baby.
The results of a CVS or Amniocentesis usually come back in two steps. The first will be a FISH panel, which will contain the results of a few of the cells, available within a few weeks. The full panel will typically be complete a few weeks after that. In most cases, the full panel results will confirm the FISH results; only occasionally will this not be the case, such as when there is a placental mosaicism – or a genetic anomaly that is confined to the placenta. This, however, is quite rare.
How do you choose what testing is right for you?
The most important thing to keep in mind about prenatal testing is that it doesn’t change a thing – it only tells you more about your body and baby and helps you make the best choices for care before, during and after birth. So when you are deciding which prenatal tests may be appropriate for you and your baby, talk with a care provider you trust about the potential risks and benefits. For instance, an amniocentesis will yield the most definitive answers, but is also one of the more risky procedures in terms of potential complications. When considering testing, ask yourself, “What would the information I learn change?” If the answer is “nothing,” then the test may not be for you. If, however, the test may yield important information about the best care choices for you and your baby, then it would be worth exploring.
Jennifer Stutzman, Freelance Writer
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