Is That Gender Genetic Test Really 99% Accurate?
Your doctor or midwife may have talked to you about the non-invasive prenatal test or screen (NIPT/NIPS). This is a test that looks at the risk for baby to have some of the more common chromosome changes that can impact baby’s health. Because it can look at the X and Y chromosomes which make up the baby’s sex, the test is often referred to in many social circles as the “gender test”.
NIPT has become increasingly popular over the past 5 yrs because it far out performs traditional blood screening tests in regards to detection rate. It is also non-invasive, meaning there’s no risk to the baby since it’s just a blood test on mom. So what’s the down-side you ask!? The biggest negative about this test is the lack of understanding about how to interpret the results.
I’ll break down the top 3 myths that that every genetic counselor wishes you knew!
1. Everything is normal!
So, if you get a result that does not indicate any high risk- this is great news! What’s key to remember is that this test isn’t looking for ALL chromosome problems that could occur, just the few that are most likely to occur. Also, this test doesn’t look for all possible genetic changes (really, there is no one test that does). So bottom line, definitely good news that results came back within normal limits, but understand that it doesn’t look for all things that could cause issues.
2. The test has a 99% detection rate, so a “high risk result” means there’s a 99% chance that baby has this condition.
It is very alarming to receive results that put you at a higher risk to have a baby with a chromosome condition. What’s super important to remember is that for us to confirm these results we absolutely need to do additional testing referred to as diagnostic testing. This includes tests such as a chorionic villus sample (CVS) or amniocentesis (Amnio).
Remember- while a test may have a 99% detection rate, it does not mean that it is 99% accurate.
The chance that your “high risk” or “abnormal” result is truly an abnormal result ranges anywhere from 30-90%. The range depends very heavily on your age.
3. This blood test is safe and replaces the other tests that can cause miscarriage
True, this test is a safe test in that it is not invasive (just a blood test) and does not pose a risk to the baby. However, it is inaccurate to think of it as a replacement test for a CVS or amniocentesis. There are a couple reasons for this. First, these diagnostic tests (CVS and amnio) are going to give you a yes/no answer vs a risk estimation that the blood test does. Second, diagnostic tests (CVS/Amnio) look at all the chromosomes and can even take a deeper look at the chromosomes to detect micro changes. Studies have indicated that 2-3% of people will receive a diagnosis via CVS/Amnio that would have been missed on the blood test. This number jumps to 6-8% if there is a structural abnormality noted on ultrasound.
So what about the risk of miscarriage from the CVS or Amnio tests? Yes, these are invasive tests, so they do pose a risk for complications that could lead to miscarriage. Most up to date data indicate that the risks for miscarriage are closer to 1/350-1/500, and some even quote closer to 1/1000. This is very different than the older numbers that quote a 1/200 risk of complications. Every institution and provider quotes their own risks- so it’s important to understand the specific risks for the center that you are working with.
Some Final Thoughts
So bottom line, NIPT is a great test that can give you really useful information, but isn’t 100% accurate and cannot look at all genetic changes. The most important question to ask yourself however is, “What information am I hoping to gain from this testing?” If you are looking for a test that can give you the most refined information on your risk for having a baby with a chromosome abnormality, then considering a diagnostic test may be a discussion that you need to have. If however, you understand that NIPT gives you info on some, but not all chromosomes and are at ease with this information, then by all means go ahead and get your blood drawn!
There’s really no right or wrong answer in how to best approach testing. I have talked to hundreds of women and families and I can tell you that everyone approaches decisions differently and in their own way. If you find yourself struggling to decide what the best route is for you, don’t hesitate to chat with a genetic counselor. That’s exactly what we are here for- to help you make sense of all this testing and guide you to making the choices that best fit you and your family.