What Are Non-Invasive Prenatal Tests Really Telling You?
March 2, 2017
Intended to offer peace of mind, non-invasive prenatal tests (NIPTs) allow pregnant women to screen their fetuses for common genetic diseases. And the results can have some pretty serious consequences, sometimes prompting moms to abort their babies. While some tests are touted as 99 percent accurate, what does that actually mean? And what are they actually testing?
The answers to those questions have been changing every few years. Susan Gross, MD, tells us that as of 2011, NIPTs were able to identify DNA pieces floating outside of cells in a mother’s blood stream. A blood test could determine if the appropriate number of chromosomes were attached to this cell-free DNA; an extra 21st chromosome could be indicative of Down syndrome. The problem? The tests couldn’t differentiate between mom’s DNA and baby’s placental DNA. So you run the risk of discovering a harmless extra chromosome — some women just have an extra “x” — and thinking that your baby has a genetic mutation.
The Panorama test seemingly solved this problem in 2013, measuring single nucleotide polymorphisms (SNPs) and distinguishing between fetal DNA and a mother’s own DNA in her bloodstream. And it can be done as early as nine weeks into pregnancy — sooner than the first ultrasound.
What Gross emphasizes — and what many panicking moms might disregard — is that NIPTs are only screenings. They can tell you that your baby might have a problem, but false alarms are not uncommon. After a three-month examination of prenatal screening tests, the New England Center for Investigative Reporting wanted to make this clear: “There is, it turns out, a huge and crucial difference between a test that can detect a potential problem and one reliable enough to diagnose a life-threatening condition for certain. The screening test only does the first.”
Is there a way to do the second? Yes. Let’s create a scenario. Your doctor calls to tell you the results of a NIPT, explaining that your fetus has a higher-than-average risk of developing a specific disorder. You’re panicking, not questioning that the numbers could be wrong. But because this was only a screening, your next move should be to take a diagnostic test, like an amniocentesis. Fair warning: amnios are invasive. Your doctor will stick a needle into your belly, extracting about an ounce of amniotic fluid, which will be tested for chromosomal abnormalities. Why don’t women just opt for this diagnostic test from the start? Because it’s more invasive, there is a small risk of miscarriage. The takeaway? While NIPTs aren’t surefire ways to identify a disorder, they are helpful for ruling out amnios. If your screening comes back totally clear, there’s probably no need to undergo an amniocentesis.
Natera Inc., the manufacturer of the Panorama test, found that 6.2 percent of women terminated a pregnancy after a screening indicated their baby had a higher risk for a chromosomal condition, bypassing the amnio altogether. Make sure you know your options, and have a clear understanding of what your test results mean. Healthy babies are not uncommon.