Many advances in genetic testing have become more readily available to the general population in recent years. Most of us are familiar with the BRCA testing for breast and ovarian cancer, the COLARIS test for colon and uterine cancer and there is also testing for fetuses well before the second trimester.
More and more it seems that patients are hearing about tests from other family members and friends and are aware of the options to determine their baby’s risk for Down’s Syndrome (Trisomy 21), Edwards Syndrome (Trisomy 18), Patau Syndrome (Trisomy 13), and Open Neural Tube Defects (ONTD) before they are even seen at the first pregnancy appointment. Our website, www.wcs-stl.com discusses the Non-Invasive Prenatal Testing (NIPT) options available for screening during pregnancy for each trimester and the advantages.
The most commonly mentioned tests by patients is the cell-free DNA test that can be performed as early as 10 weeks gestation. It is also the test that can disclose the gender of your fetus at its earliest possibility. As with the BRCA and COLARIS testing, cell-free DNA testing is very expensive and there are certain criteria that must be met in order for an insurance company to cover the testing. As a side note, even if the testing is a covered benefit, it may still apply towards your deductible so it is not necessarily free. The criteria states that a female must be at least 35 years of age at the time of delivery which is considered advanced maternal age (AMA) or must have a prior pregnancy with aneuploidy (an abnormal amount of chromosomes).
When these tests were originally released the manufacturers of the tests were offering special pricing and were not submitting the claims to insurance so the tests were more affordable than they are today. Now they are approximately $1,000 with an additional fee to disclose the gender, even though the lab has to determine the gender in order for the results to be confirmed.
Aside from the monetary cost there is an emotional cost as well for patients receiving the testing that do not fit the criteria. Original studies performed on AMA patients show these tests have 99.9% sensitivity and specificity. This essentially means that 99.9% of the time the test results are accurate to whether or not a fetus has any of these genetic mutations. Sounds like a great test right??? Well, it is when used the appropriate population.
For women that do not fit the criteria, mainly for age, the positive predictive value decreases. For example, if you are 35 years old and your test comes back positive for Down’s Syndrome(DS) there is a 95% chance that your baby truly has DS and a 5% chance that it was a false positive test. However if you are 30 years old the chance reduces to 88% that your baby has DS and 12% chance that it is a false positive and if you are 25 years old the chances are 82% and 18% respectively.
Those numbers are certainly concerning if you are among one of the patients with a positive result for DS but looking at the same ages and percentile risks for Trisomy 18 the numbers are much more alarming.
- Age 35yo, there is a 75% chance that your baby has Edwards Syndrome and a 25% that it is a false positive.
- Age 30 yo has a 55% chance of Edwards Syndrome and 45% chance of false positive.
- Age 25yo there is a 44% positive predictive value and 56% chance that is it a false positive .
So as you can see in women who do not fit the criteria, mainly maternal age at delivery, the risk of the test being a false positive increase even above the chance of it being a true positive. The only ways to confirm true diagnosis is by undergoing invasive prenatal testing such as either Chorionic Villus Sampling (CVS) or Amniocentesis, both of which carry a risk for miscarriage and are also discussed on our website as well.
So, although health care providers are required to offer patients genetic testing during pregnancy, there are certainly advantages and disadvantages to each test. It is always up to the patient as to which test is requested, if any at all. Recommendations are often made by health care providers on an individual basis as to which risk factors are present and which criteria are met but at what cost financially and more importantly emotionally is it to have testing done that is not necessary only to determine your baby’s gender in the first trimester. After-all, it’s not going to change.
The published statistics are estimates that were obtained by the Positive Predictive Value of Cell-Free DNA Calculator from University of North Carolina at Chapel Hill and are used as a counseling tool for healthcare.
The topic of cell-free DNA interpretation was also recently editorialized in the American Journal of Obstetrics and Gynecology by a physician at Washington University in St. Louis, School of Medicine, George A. Macones, MD in the July 2015 issue.
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