How accurate is the new blood test for Down syndrome?

Dice open sourceWhen receiving a test result from the new blood test for Down syndrome that says “positive,” do patients understand there may be a one-in-five chance of a false positive? Or even a one-in-two, depending on the mother’s age? Even genetic counselors admit this is difficult to grasp.

Yesterday, I featured an article from the New England Journal of Medicine raising concerns about Non-Invasive Prenatal Screening (NIPS), the new blood test for Down syndrome, being offered by Sequenom, Ariosa, Verinata, and Natera. The article cautioned against offering NIPS to every expectant mother. One reason noted in the article was that:

Arguably, PPV is more important than sensitivity and specificity to patients undergoing testing: it indicates the probability that a positive test result indicates a true fetal aneuploidy. Thus, PPV should be discussed in study reports and marketing materials but isn’t.

In a post on a blog for genetic counselors earlier this month, a genetic counselor further explained the importance of PPV and how it is not being understood with NIPS results.

Katie Stoll is a genetic counselor in Washington State. On the blog, The DNA Exchange, she examines the role of the incidence rate for Down syndrome and a test’s Positive Predictive Value (PPV).

The NIPS labs (and the media reporting on them) highlight their sensitivity and specificity levels as being greater than 99%–meaning their tests can identify greater than 99% of those pregnancies carrying a child with Down syndrome and rule out greater than 99% of those pregnancies not carrying a child with Down syndrome. But, unless some further calculations are done, a mother cannot understand how likely receiving a “positive” NIPS test actually means she is carrying a child with Down syndrome. As Stoll explains, this is because of the role of the condition’s incidence rate.

Incidence rate is how often a condition appears in the population. Down syndrome remains a rare condition, becoming rarer the younger the mother is.

Stoll takes as her example a population of 100,000 35-year old women who have an incidence rate of 1-in-250 carrying a child with Down syndrome. Therefore, of the 100,000 35-year old moms, 400 will be pregnant with a child with Down syndrome (100,000 X 1/250 = 400).

NIPS labs report a sensitivity rate of 99.5%, meaning 99.5% of those actually carrying a child with Down syndrome will be detected by NIPS. Therefore, of the 400 35-year old moms, 398 will receive a “positive” NIPS result (400 X 99.5% = 398). Note as well that 2 will receive a “negative” NIPS report–a false negative, since they are carrying a child with Down syndrome.

NIPS labs also report a 99.9% specificity rate–the percentage of those pregnancies not carrying a child with Down syndrome that will receive a negative NIPS report. In Stoll’s example, there are 99,600 moms not carrying a child with Down syndrome (100,000 moms – the 400 carrying a child with Down syndrome = 99,600). Of those 99,600 moms, 99,500 will receive a negative report (99,600 X 99.9% = 99,500). This then means 100 will receive a “positive” NIPS result (99,600 – 99,500 = 100)–making these 100 false positives.

So, in this example, there were 400 pregnancies actually carrying a child with Down syndrome. Of these, 398 would receive a positive NIPS result, but 100 false positives would also be reported, making for a total of 498 positive NIPS reports when only 400 pregnancies were actually carrying a child with Down syndrome. This means that a positive NIPS report means the mother has a one-in-five chance of a having a false positive (100 false positives / 498 = 20%, or 1-in-5). And, this false positive rate goes up the lower the incidence rate.

Take for example 100,000 expectant moms in their late 20’s. The incidence rate is about 1-in-1,000. This means there are only 100 moms actually carrying a child with Down syndrome (100 X 1,000 = 100,000). Of these, 99.5 would receive a positive NIPS result, given the 99.5% sensitivity rate. But, 100 of the moms who were not carrying a child would also receive a positive NIPS report (100,000 minus the 100 carrying a child with Down syndrome = 99,900 X 99.9% (specificity rate) = 100). So there are 100 true positives and 100 false positives reported. A “positive” NIPS result in this low risk population means only a 50% chance of actually carrying a child with Down syndrome (100 true positives out of 200 total positive reports = 50%).

Stoll’s post and the New England Journal of Medicine article make the same point: the accuracy of NIPS remains unknown because of the way the labs report both their research and their test results. The professional societies have called on the NIPS labs to standardize their reporting so the accuracy of each companies’ test can actually be determined. The NIPS labs have not done so, but as these articles, and hopefully this post demonstrates, a positive NIPS result is not a true positive.

Update: the subsequent posts in this series explain positive predictive value and its relation to maternal age, with graphs visually displaying the percentages. See these posts at this link and this link.


  1. Thanks for crunching the numbers on this. The claims to accuracy look a whole lot less impressive when you see what it actually means.

  2. Mark, I can’t tell you how much your articles are giving me hope for a healthy baby. I am 28 years old and recently received Panorama results with a 99/100 chance for my little boy have T21. I am still so confused and sad about such results. I took the Panorama due to two spots on his heart. After receiving the Panorama results I met with a genetic counselor, MFM ultrasound specialist, and followed that with a fetal echo cardiologist specialist. The 2d and 3d ultrasound depicted a healthy baby from head to toe with no further markers from the MFM specialist. Additionally, the fetal echo cardiologist ultrasound showed a perfectly healthy heart with only the two calcium/soft markers showing. However, when I talked to the genetic counselor she informed me the Panorama is 99% accurate and by receiving a positive result it is pretty much a guarantee that he has T21. I know the ultrasound does not diagnose T21 but I find it so hard that his eyes, nose, neck, feet, spine, leg and arm length showed no sign of T21. He was measuring at 50th percentile. I opted to not have the amnio as we will raise this child no matter the circumstances. We have known of this information for three weeks and I still have 12 weeks remaining until my due date. I am so confused and the anxiety is killing me. I have contacted Panorama as well as quest diagnostics and both companies refuse to talk with me. Both companies refer me to my Dr. My Dr. Office has only used this test for a few months and I am the first test to show positive.

    • Thank you for your comment and I’m glad my writing has provided you comfort. Anxiety is barely discussed, despite it being almost ever present in prenatal testing. It is unfortunate that your genetic counselor suggested that a NIPS result is “pretty much a guarantee,” since given your age and your other prenatal tests, i.e. the ultrasound, would suggest the NIPS results may still have a high false positive. Nonetheless, I would suggest reviewing the book, Diagnosis to Delivery, which is available for free as a .pdf at The book is written for mothers with a positive result who intent to continue their pregnancy, and addresses the issues mothers have reported when they have known prenatally that their child will have Down syndrome. While your case remains a maybe, the book can help prepare you in the event that the Panorama test is indeed correct. Regardless, it sounds as though your child is developing well and I hope that you have a healthy, and smooth delivery.

    • Dear Ms. BETHK, Thanks for sharing your life experience. Sorry to be nosy and I apologize in advance, we have had a positive Panorama test as well and was wondering if your baby turned out to be ok?.

      Thanks and god bless.

      • Our baby does in fact have down syndrome. Fortunately our little one did not need surgery as we feared shortly after birth so health wise there is no issue there and all other tests have come back great. I can tell you once the little one arrived the diagnosis was much easier to deal with emotionally. I will be praying for the best for you and your family.

        • Beth–I’m glad to hear your baby did not need surgery. And I understand Harry’s phrasing of wondering if your “baby turned out to be o.k.,” but I hope you will share my appreciation if you don’t already that our children with Down syndrome are o.k., even with having Down syndrome. I further hope you are receiving the support you need and have found helpful written resources. The National Society for Genetic Counselors has a list of approved resources at this link. I particularly appreciated Babies with Down syndrome (we had a postnatal; the book can be overwhelming particularly prenatally, but it helped in providing information in a postnatal setting); I found “Expecting Adam” to be extremely well written and a unique way of experiencing having a child with Down syndrome; and I know many mothers, particularly, who enjoyed the stories shared in Gifts. I contributed a chapter to Gifts II. Congratulations on the birth of your child.–Mark

          • I understand where he is coming from with the wording. No hurt feelings here.
            I am about ten pages into Gifts and it is my favorite book regarding DS. I will be sure to check out Gifts II. I didn’t realize there was a second so I will definitely look for this book as well.

          • I’m glad you’re finding Gifts a useful resource. From my post from yesterday, we found it tremendously helpful to link up with our local support group and talk with fellow parents. I wish you and your child well.

          • Thank you again for your words of wisdom and support. I look to seek a local support group soon. It has just taken me some time to be at a place where I am mentally ready to partake in a support group.

          • Beth and Mark, Thanks for being an awesome support, I truly appreciate it, I am glad to hear Beth that your little one did fine and you are enjoying your parenthood, again if I used the wrong choice of words I apologize with all humility. Once again this blog give us all so much hope and support, cannot thank you two enough.

  3. GiveMerealScience says:

    What kind of test is that? It sounds that the test has 99% specificity (true positive) but 99% sensitivity (false positive). Is it like 50/50 chance?

  4. My friend is 44years old and 4 months pregnant. The test results are 1:42. She does not know how much of baby being with downs syndrome. She wa just she is a positive and to research on internet what that mrans. She is so broken now even considering abortion. They told her they will di amnioscentesis in january and give her an option of abortion then
    I heard that this amnioscentesis can also be risky to baby. Please help us understand these results before this dreaded abortion.

    • A report of 1:42 means that she has a 1 out of 42 chance that her child has Down syndrome. This can also be understood as a 2% chance of having a child with Down syndrome. You’ll see at the chart in this post, though, how she had a 2% chance based just on her age, so the test really does not show much of an increased chance for having a child with Down syndrome. The test that provides a diagnosis in the 2nd trimester is an amniocentesis and it does have a risk of miscarriage associated with it. Studies report a wide range, from less than .5% to over 1%, but really the only relevant rate is the one your friend’s doctor has with his or her procedures, so that is something to ask about. I hope your friend will review the resources recommended by medical professional organizations at the Prenatal Resources tab to provide her up-to-date, accurate information about what it means to have a child with Down syndrome.

  5. I did the Panorama test with Natera and received and 87% chance of DS. My baby was born with DS in October. I just wanted to pass along the score and the results because when I was researching what everything meant while I was still pregnant, it was difficult to find a score that was high but not in the nineties range.

    • Thank you, Angie. I hope your baby is doing well.

    • I’m 24 years old and just did the panorama test and if came back 90% chance so I’m worried to death they give me the option for the test because she has an eif I’m 28 weeks pregnant and just worried and confused.

      • Based just on your age, your Panorama result would mean you have almost a 60% chance of a false positive. I’m not sure how having an EIF would adjust your baseline chance. I would suggest having your doctor follow up with Natera, Panorama’s lab, to get clarification on what is the positive predictive value for your test results.

      • karina veras says:

        did your baby end up having down syndrome? i am currently in the same exact boat as you.

        • LUVYS PEREZ says:

          I am 38 years old. My panorama results came back with a 99% high risk of T21. I am so confused and devastated. 😢

          • See the links in this post, specifically the link to the PPV calculator. Based on your age, your positive predictive value, i.e. the chance that your child has Down syndrome (T21) is about 88% with a 12% chance of the test being a false positive. Please also see the link for Down syndrome resources as you should have received that information as well with your test result.

  6. I took the MaterniT21 test in Feb 2013 and it came back positive for Trisomy 21. I was told by my fetal maternal specialist that it was 99% accurate. I opted for a CVS test which came back inconclusive! The report indicated possible mosaic downs. I then met with a geneticist who explained to me the difference in the tests, and how results are determines. Amnio is the only test that actually cultures fetal cells. The CVS only cultures placental cell and it cases of Confined Placental Mosaicism the CVS can be wrong as well. I did the amnio on advice of Geneticist and it came back perfect. I went through 5 weeks of hell! I would NEVER knowing what I know now choose one of the screening tests again. IMO they are misrepresented and I also do not believe they properly report it when the have false negatives and positives. I was nervous my whole pregnancy but my baby was perfect.

    • Thank you for sharing your experience, but I regret it was as harrowing as it was. In 2013, the American College of Medical Genetics & Genomics issued a statement noting tests like MaterniT21 test placental cells. In 2015, the National Society for Genetic Counselors issued a statement noting the same limitations of CVS as you mention, i.e. that it tests the same cells as tests like MaterniT21.

    • I took the panorama test and it came back positive. It turned out that I did in fact have a ds.

  7. I am 22 years old and just received a postive MaterniT21 result for Trisomy 21. This came as a huge shock to my husband and I, being that we are so young and this is our first baby. We did have two soft markers on ultrasound (mildly echogenic bowel and nasal bone hypoplasia) which is what prompted the blood test. We have had a week to process the news and are still so confused. We declined amniosentisis because the risk that is involved. I have 4 months until I deliver and I’m just trying not to worry the rest of my pregnancy. We are standing in faith that our baby will be born healthy, but at the same time, preparing for the possibility of him being born with Down syndrome.

    • Aislinn–as discussed at this post, MaterniT21 never reports a true positive (or a true negative), which your concluding sentence suggests you already knew. At your age, chances are still more likely that your child does NOT have Down syndrome, as the positive predictive value for your result is only around 40% (see the graph at this post). That said, you do have an increased likelihood for having a child with Down syndrome based on the MaterniT21 result. Please visit the Prenatal Resources page to find a listing of professionally recommended resources that you may find helpful as you prepare for the possibility of having a child with Down syndrome.

      • This post gives me much more hope than the accuracy the company reports. Thank you for taking the time to spell out what the numbers actually mean.

      • Hi Mark – Something to keep in mind is that the the positive predictive value should be based on the a priori chance of having a baby with Down syndrome. Yes, using just her age and an assumed gestational age of about 20 weeks, the positive predictive value is around 40%. However, the PPV would be higher in this case because of the presence of the two markers. Her a priori chance is higher than that of a typical 22 year old.

        Aislinn – I would recommend that you contact a genetic counselor/MFM to help explain the significance of your result, if you haven’t already. Good luck with everything and congratulations on your pregnancy.

        • Right you are. Of course, this would all be clearer if Sequenom and other NIPS labs simply reported the PPV with their test results instead of the misleading “positive” or “negative.”

          • I agree that the reporting can be confusing. Certainly, a lab can use the age-related risk and the Z-score to calculate an individual risk for a patient. However, it is not feasible for the lab to take into account every variable such as ultrasound findings. It really is up to the provider to use their clinical judgment in counseling a patient regarding the significance of the result. The lab reports also do say that NIPS is not a substitute for diagnostic testing. Unfortunately, there are many OB providers who order the test and aren’t able to interpret the results correctly. However, genetic counselors/MFMs have more experience with this. Regardless of the exact PPV, the chance of the condition after a “positive” result is high enough that it is reasonable to consider a diagnostic test because it would be higher than the risk involved with an amniocentesis. Of course, diagnostic testing is always optional, though it should absolutely be performed before a pregnancy termination if that’s what the couple decides on. We are very clear about that. We are also clear that it can be beneficial to know about Down syndrome and other conditions prior to birth – termination is certainly not the only reason to have testing. I had a patient who had an increased chance of Down syndrome on a screening test. She declined amniocentesis and has an adorable daughter with Down syndrome. She adores her, of course, but she said later on that she wished she has known ahead of time.

          • Sounds like you’re doing what’s recommended and providing good care, but as you recognize, it’s a challenge of supply vs. demand: the supply of well-educated medical providers, GCs, & MFMs, versus the demand for testing (generated in no small part by the aggressive marketing by the NIPS labs). Increasingly, moms are making the decision you relay at the end: to rely on a NIPS screening result to prepare, but understand they may have a false-positive. I had not heard, though, of moms regretting not having a definitive diagnosis if they chose the option of relying on the NIPS result and decided to continue their pregnancies.

          • I agree – I’ve had patients with NIPS results that were “positive” for Down syndrome and they have chosen to continue the pregnancy under the assumption that the baby has Down syndrome. The patient I had who regretted not knowing had a traditional screening test showing a 1/5 risk and this was before NIPS.

          • I wondered & half expected that was the case. While persistent anxiety has been reported even with NIPS, it was a known possibility that moms would always be wondering based just on a traditional screen.

  8. My age 37 and an nt of 3.5 put my risk if a baby with d’s way up….. had harmony and they came back as very low then the 20 week scan nt at 4.4 and everything healthy….. no idea what to think…? Really dont want to run the risk with amnio…

    • Naomi–from the beginning the only way to know for sure prenatally was with an amnio, and unfortunately you’re having the common experience with screening of not having the results allay any anxiety. While a screen-negative Harmony result is often relied upon by mothers wishing to avoid the risk of miscarriage from amnio, being a screening test, false negatives still occur. I would discuss your NT measurements and Harmony result with a genetic counselor or MFM and see if they have experience with other patients with similar contradicting results.

      • Thanks Mark. If I had the prior knowledge I would have done CvS but it was offered to me. They pushed the harmony test. Also in both scans the tech admitted having trouble getting good views and I wish I asked to return and try again the next day. On the Thursday the tech got an nt of 6.4 then 5 days later a different tech and machine got 4.4……. and the peritanologist was happy with pics so I’m terribly confused.

        • Troubling to hear. I hope the care you receive improves in both accuracy and compassion.

          • just wanted to say that Oscar was born on Dececember 31st 2015. He doesnt have downs and is doing really well. i appreciate the time and knowledge you gave me. xx

  9. This is a brilliant and well written article. What confuses me is that I had 2 combined nt tests giving me a 1:2 & 1:3 chance of t21 and a positive 1:2 harmony result which I believe is the highest risk they give. So do I have a true 50% chance or is it virtually conclusive? I’m 37

    • If those ratios are presented as positive predictive value (PPV), then the highest PPV quoted is only a 50/50 chance, i.e. 1:2 or 1-in-2 chances. That is not the highest cell free DNA PPV result; it can be as high as 9:10 or 9-in-10 or a 90% chance if the mother is over 40. I would have your results interpreted by a genetic counselor or medical geneticist to ensure they are understood correctly.

      • Wow this is a really interesting article and I’m glad I found it. I am finding out tomorrow the results of an amnio, i went for the NIFTY nipt test first to try and opt out of the amnio however my results came back as 99% chance…very unassuming. I feel so strongly that my baby is fine but these results have deterred me, I am 35, had a 4mm NT result but everything else was ok…will see tomorrow I guess and find out if I’m lucky enough to be a false positive statistic…?

        • Whoops spell check, unassuring, not unassuming!

        • Unless you had a conventional screen result prior to having NIFTY, then it’s results based solely on your age will never be “99%”. See this link. If your results are based just on your age, then you have a greater than 25% of having a false positive. I hope you get better information with the delivery of your amnio results.

  10. I am so confuse with what is going on. I am 16wks and got a positive of 1 in 460 test results. Please help me understand I am getting worry and could not sleep or stop thinking.

    • Click the links at the bottom to show what your positive predictive value is, but it sounds like you received a PPV of 1-in-460. To understand your results better, if you don’t mind me asking: what is your age? did you have a conventional screen result prior to having cell free DNA testing? and, what condition did your test say you tested “positive” for?

      • I’m stressed I’m 34 years and found positive D’s and I’ve got T21.

        • I’m inferring that you had a cell free DNA screen result report back “positive” for Down syndrome. According to this calculator, what that means is you have a 75% chance of your test result being a true positive and a 25% chance that it is a false positive–so, a 1-in-4 chance that the test result is incorrect. Most accept prenatal testing hoping for reassurance from the information it provides; this link is for a recommended resource about Down syndrome that may provide some reassurance, as well.

  11. I am 37 yrs old and 16 weeks pregnant with a PGS tested embryo. The Panorama test came back with low risk 1 in 10,000 for t21. However when I went for my 12 week screening the blood screen came back as 1 in 5 chance for t21. The NT measurement at 12 weeks was 1.6mm and the one at 16 weeks was 3.6mm. The genetics team have said the Panorama and PGD tested embryo seem to be more ‘reliable’ than the 1st trimester screen. But I just can’t help shift the 1 in 5 report……Can two tests give false negatives?should I have an Amnio?

    • It would be incredibly unlikely that PGS or Panorama would report a false negative and therefore even more unlikely if both were to be false negatives. Conversely, NT scans have a much higher false positive rate than the Panorama false negative rate. Whether you should have an amnio turns on your assessment of whether the certainty of knowing from a diagnosis is worth the risk of miscarrying pregnancy, particularly given the high likelihood based on PGS and Panorama that your child does not have Down syndrome.

      • Thanks for your reply Mark. That’s exactly the dilemma I have. The scans to date have all been within ‘normal limits’. That is reassuring. There is some talk that a low level of Papp-a hormone (0.2 mom) has caused the high risk 1 in 5 result for t21 and 1 in 30 for t18. The hcg was 1.35mom. There was brief mention that low Papp-a could be down to ivf process. Have you come across low Papp-a and cause for ‘high risk’ biochemical results in your research at all?

        • Drilling down into the subcomponents of serum screening has not been something I have focused on, and even if it were, I would defer to the medical experts on those technical matters. While ultrasound findings are typically just soft markers, I wonder whether a Level II ultrasound would further inform the chances of T21 or T18, and it has the benefit of being non-invasive.

  12. Carrie Copeland says:

    Im 42 years old and 13 weeks pregnant. My n/t ultrasound was normal bit my materniT 21!screen came back saying my baby would have a very high chamce of Down’s syndrome. I was advised that the cvs will give the same result and not to bother having it since it was also testing placenta cells and not the baby’s only. I am sick from anxiety and sadness. The genetic counselor told me that I can have amnio to know for sure but that this test had “statistical analysis” and is very unlikely to be wrong. I can’t make sense of what this all really means. Is there any real hope that the Down’s syndrome is not trie? Or no? I am so confused by statistics, professional’s advice to me, and feel like because of my age, it might be hopeless. Im hoping you can shed some light for me. Thank you for anything you can explain.

    • Based on this PPV calculator, a screen-positive result like MaterniT21 for Down syndrome at your age would mean you have a 96% chance of having a child with Down syndrome and a 4% chance of a false positive. It sounds like your genetic counselor has an inflated view of the accuracy of these types of test. The only way to know for certain is with an amnio and amnio’s are recommended to confirm any screen result before making any reproductive decisions. Further, professional guidelines recommend that you receive written and support resources with a screen-positive test result (and in some states, the law mandates the provision of these resources). You can find these resources at the Prenatal Resources tab. I hope you find them helpful.

      • Mr. Leach,
        Thank you so very much for your replies and all of this extremely helpful information. This is the first site I have found that has actually given me clarity.
        I truly appreciate your efforts. THANK YOU.

      • Jennifer says:

        Hi there,I am 21 weeks pregnant and had an ultrasound last Thursday, April 28 which showed one soft marker, a nuchal fold of 6.9 mm. I have been referred to a genetics councillor and had the Panorama test done today. As I wait for my results, I wonder what you would think the rate of false positives/negatives would be for my age group, I am 31. I am just worried this test will come back inconclusive or high risk. I have had no other testing done (since I know how common false results are with these screening tests), and this is the only testing I have done. The rest of my ultrasound at 20 weeks was totally normal, and the OB is a high risk OB and noted the nasal bone is present and clearly visible and did a thorough examination of the heart and all chambers. Any insight would be much appreciated. They currently have me as a 2% risk.

        • Based on your age, if the Panorama screen returned a screen-positive, you would have a 36% chance of its being a false positive. I’m not sure what your providers are basing their 2% chance on, but if that is used, and your Panorama was screen-positive, then you would have a 15% chance of the result being a false positive. You can run the numbers at this on-line calculator.

          • Jennifer says:

            Thanks! The 2% is what they came up with based on my age and the nuchal fold measurement from my ultrasound last week, since I didn’t do any other testing. Hoping to have a negative result from the panorama but just wondered if amniocentesis should be considered if we do get a positive. After having two early miscarriages I am just so nervous about any invasive testing. We are fortunate to have one beautiful healthy boy already. Think positive thoughts for me!! I truly appreciate your help.

          • I am not familiar with nuchal measurements being considered reliable indicators of Down syndrome or other conditions when measured beyond the first trimester. To know for certain, amnio was always the only test that could provide that level of certainty. Therefore, if you would do anything differently about your pregnancy after a positive Panorama result, then professional guidelines emphasize that diagnostic testing is needed to confirm the Panorama results, since tests like Panorama are still just screening tests and have false positives and false negatives. You mentioned miscarriage which is discussed in this post. If you search for posts on this blog that begin with the headline “Our story,” you’ll see that I, too have a beautiful healthy boy and girl.

        • hi i had the same nf of 6.9 no other markers but im 37yrs old. i did the harmony test which came back negative 1:15000. i had a healthy baby boy on dec 31 2015. so wait for your results. ps oscar still has a chubby back neck lol.
          wishing you a very healthy happy baby xx naomi

          • Jennifer says:

            Just received my results, negative and low risk for all trisomies – less than 1/10,000 risk. So the 6.9mm nuchal fold did not indicate Down syndrome for us. Thank you for your reply – it truly helped me to relax!!

          • Thank you for sharing your results. I hope you get the support and care you deserve and have a healthy delivery and recovery.

  13. I just got my test results back from this new testing and was told is a 91% chance my baby has down syndrome. I am 38 and this will be my 3 child. I am confused …..

    • Based on the calculator linked at this post, your chances of having a child with Down syndrome are 88%, not 91%, with a 12% chance that your result is a false positive. I hope you’ll read the post with the calculator as well as the other helpful resources linked at that post.

  14. Beatriz says:

    I have a 1/46 chances of having a baby with down sindrom . I did the blood test and it was 96% chance of having a baby with ds . And there is sotf markers like fluid white spot in her heart. Nasal bone is present and neck size is normal . Im 22 years old should i be worried? Or theres hope for my baby?

    • I’m not sure what your 1/46 chance is based on. Based just on your age, if you had a cell free DNA screen result that was positive, it actually has a 51% chance of being a false positive. Please see this post and the helpful links in it for more information.

  15. Alex0408 says:

    I’m glad I found this article. I’m 28 and was told my baby is at high risk for prader willi syndrome which is 1 in 22.. They also gave me a probability of the panorama result being false positive is >99%. Genetic counselor has suggested for amnio.. I’m so scared and confused considering the risks associated with it. Please suggest if I should go for amnio or not..

    • Even if Panorama had a stated accuracy of 99% for detecting Prader Willi, a screen positive result would still mean that you have a greater than 99% chance that the test result is a false positive. Professional organizations do not recognize tests like Panorama for testing for conditions like Prader Willi. The only way to know for certain is to either have an amnio or have your child karyotyped after birth. See this post for other helpful information on cell free DNA screening and a calculator for you to see for yourself how unlikely it is that your child has PWS.

  16. Hello, I’m 42 years old. I’m considered high risk for trisomey 21 after panorama with 91% positive predictive value of 91%. The fetal fraction was 7.9%. However, the trans-nuchal ultrasound at 12 weeks was normal. What are the chances it could be a false-positve? Thank you so much!

  17. Hi Mark,

    My wife just had the Visibilit test by Sequenom done (blood was drawn at 10 weeks & 2 days). She turned 29 in Novemeber of 2016. We were devastated to get the results back from the doctor, presented to us as being >99% chance of our baby having DS. After researching on your website I began to develop some hope, I calculated about 50% PPV and the online calculator you linked is returning about 56% PPV. I couldn’t get a PPV number from Sequenom and they weren’t able to give any more accuracy on the sensitivity and specificity numbers than >99% (sensitivity) and >99.9% (specificity). Age related risk provided is 1/972 and Post-NIPT risk is >99/100, which I’m unsure of what this Post-NIPT risk number means (any insight?).The fetal fraction was 9%. Our current plans are to meet with a genetic counselor and get the CVS procedure done next week at 12 weeks 1 day. I’m still concerned with getting similar results from the CVS if it could be fetoplacental mosaicism. I was hoping you could help me verify that the PPV I am getting is correct and possibly give some guidance on if CVS is the best next step going forward. I really appreciate all the information you have gathered and look forward to hearing from you.

    • I don’t understand Sequenom saying “Post-NIPT risk is >99/100” and I’d ask them to clarify. Your calculations on PPV are correct. And, you’re right that CVS, because it tests the same source for DNA that VisibiliT does poses a risk of returning a similar false positive result based on placental mosaicism–though how much of a risk, I’m unsure of and perhaps something your GC can counsel you on. I expect you found the calculator link from this post, but if not, feel free to scroll to the end to also click on the resources regarding Down syndrome. Thank you for sharing your experience and frustrating that more accuracy is not provided from the lab.

      • Mark,

        Thank you so much for the quick reply. I was able to get a PPV from Sequenom. They have a genetic counselor they consulted that apparently used the same online calculator giving a 56% PPV. We were more than encouraged with that news after originally believing it was >99% chance. Next step is to meet with genetic counselor and then to perform CVS to see if it gives us any more clarity. I will keep you updated on what I find out about the Post-NIPT risk.

      • Mark,

        I have not had any clarification on the Post-NIPT>99/100 but I think it means that their rate of true positive results is >99/100. Today, we spoke to the specialist who will be performing the CVS for us. He said that Sequenom is reporting that they have had 1,068 VisibiliT tests so far with 21 of these tests that came back as high risk for DS like ours. All 21 tests were confirmed to be correct, and the babies all had DS. It was not clarified how these tests were confirmed. What is shocking to me about this information is that 21/1,068 is about 1/50 women tested had a child with DS. Based off of statistics, it seems to me that this would mean the average age of the women tested had to be in the 40-45 year range. After giving us the news that the test was 100% so far, this particular doctor gave us the slim chances of, at most, a 10% chance of a baby that does not have DS. After first being told that it was a 99%+ chance of our baby having DS from our OB, I’m starting to cast extreme doubt over anything I am told. Am I misinterpreting these results, or do you think I am correct in still believing the 56% PPV number? We feel like we are on a roller coaster of highs and lows with all of the contradictory info we have received, trying to not be too optimistic, but also trying to not lose complete hope in a healthy baby. Again, I am so appreciative of your advice/help.

        • Your PPV calculation remains the correct one. They’re reporting based on the experience they’ve had in their clinic, but, as you note, they don’t share how the screen results were confirmed. If you decide to proceed with the invasive procedure, I hope it and the recovery goes well.

          • Mark,

            The CVS procedure went well. Prior to the procedure, the ultrasound showed a NT of 2.1, a defined nasal bone, heart in the right placement, and only one stomach bubble. Very encouraging to get those results, although the doctor still gave us only 10% chance of having a healthy baby. I feel like this outlook was extremely pessimistic and constantly wonder why he refuses to change his outlook despite having more evidence pointing towards a healthy baby. We get the FISH results Monday and are praying for good news.

          • Glad to hear the procedure went well. Note that FISH results are still considered screening results; only the full results are diagnostic.

  18. I’ll preface this by saying we live in the Arctic and have had a horrible experience with our prenatal care so far, including incorrect information about the results of our prenatal testing. We chose to do the Harmony test and paid for it ourselves at about 15 weeks. It came back negative with a less than 10,000 risk for DS. We then did the (free) MSS test. When the results came back at 22 weeks, we were provided with the wrong numbers and were told our risk had come back as 1:340. Since I’m 35, they were reading the wrong numbers — that was simply my base risk starting off, as you already know. Nevertheless, we were offered the option of an amnio as they claimed they had no way of reading the MSS in conjunction with our Harmony results and giving us an updated risk based on the two together (I know, I have no idea why). After a week of hellish waiting for the amnio to be scheduled, they called back and told us they had finally had a lab check the MSS with the Harmony and there was now no reason for the amnio. We were so relieved we asked very few questions. A few days ago, in a different prenatal appointment with a visiting doctor, I found out the real MSS test result was actually 1:2 not 1:340 and acquired a copy of the test. I am now 30 weeks and they will not provide an amnio as they are sticking by their earlier claim that the Harmony test results override the MSS, even though it’s 1:2.
    Unfortunately, my mind is not exactly rational at this point and the 1:2 is all I can think of — and the fact that they will not allow us the means of finding out conclusively with a diagnostic test. I know the MSS has a much higher rate of false positives, but still, one of the tests is right and one of the tests is wrong, and without a diagnostic there is no way to know which is which. Is this normal? Should they be offering the diagnostic still or should we just be accepting of the Harmony result and willing to ignore the MSS?
    I’m not sure if you even have time to read all of the comments you probably receive, but I am feeling very desperate, scared, and alone — to the point where I am leaving a comment on a blog… I have read your other responses and was surprised you took the time to carefully reply to each. If you have the time for this one, I would be very, very grateful for any opinion.

    • Under the current guidelines, screening tests like Harmony trump conventional screening tests like MSS for conditions like Down syndrome, Trisomy 18 and 13. I am presuming the MSS 1:2 result is for Down syndrome; if so, the Harmony test trumps the MSS result as tests like Harmony are more accurate than MSS. Regarding the amnio, I believe they are at the outside edge of when an amnio can safely be performed as the pregnancy has advanced to where there is not as much room for the needle to safely enter the amniotic sac. If you are seeking reassurance, you could request to have the Harmony redone. Screens like Harmony are actually even more accurate the later in the pregnancy they are performed because there is more cfDNA to be tested. If you were to get a second screen negative from Harmony, that would be highly indicative of a true negative. You may have to pay out of pocket for the Harmony test, but may be able to negotiate the cost given your circumstances.

      • Thank you so much for the reply, Mark! That is so incredibly good to know! I had wondered if the Harmony test could be done twice for extra security. Knowing it might be even more accurate is so helpful. We had to pay out of pocket for the first one, anyhow. It would be worth it for the peace of mind. Again, I would rather know what’s happening than not know, at least now that we have already begun this process of testing…
        Thank you for being willing to answer questions and take the time.

  19. Stephanie says:

    What would the false positive chance/ PPV be for a 27yr old and a positive* Maternit21 test? Does other positive testing such as a enlarged NT during a scan make false positives less likely?

    • According to this calculator, the PPV for a 27 y/o with a screen positive cfDNA result is 54% with a 46% chance of it being a false positive. NT by itself is not recognized as an accurate screening method. More information with links to fact sheets and resources can be found at this post.

  20. Hi, I am 28 years old and I’m 19 weeks pregnant with my second child. My blood tests came back positive for Down syndrome. They told me is a 1/200 chance. I have an appointment with a genetic counselor and a detailed ultrasound. What are he chances of a false positive, mg husband and I don’t have a history of Down syndrome in our family. Thank you

    • If you had cell free DNA screening (AKA “NIPT”), then, according to this calculator, your chances of a false positive would be 44%. But, because you represent your odds as 1/200, it sounds like you had conventional maternal serum screening. As such, the chances that yours is a false positive is 99.5%. I hope your appointment with the genetic counselor provides helpful information.

  21. Kathy le says:

    Hello, I’m 35 years old. I’m considered high risk for trisomey 21 after progenity with 72% positive predictive value. However, the trans-nuchal ultrasound at 12 weeks was 4.5mm What are the chances it could be a false-positve? Thank you so much!


    • According to professional guidelines, cell free DNA screening like Progenity trumps conventional screening like the nuchal-combined screening for conditions like Down syndrome. Therefore, your chances that your test result is a true positive is 72% and you have a 28% chance that it is a false positive.

  22. Kathryn Gorham says:

    I am 37 years old and will be 38 when the baby is born. My quad screening showed 1 in 38 of down syndrome. I am waiting on the results from Maternity21 for confirmation. My OB doctor states that this test is 99 percent positive. I have cried for days waiting on reaults.

    • Review this post and feel free to share the fact sheets linked in it with your doctor so that your doctor has a better understanding of the accuracy for cell free DNA screening tests like MaterniT21.

  23. Hello, I am very confused with this whole process. I’ve had the 12 week scan combined with blood test and was given a 1:148 ratio for tri21. I’m 28yrs old and the only indicators were the NT was 3.1mm and combined with my blood work (which my OBGYN didn’t not seem overly concerned about). The genetic counselor was very doom and gloom and gave us the option of the NIPT blood test or CVS/amniocentesis, and chose to do the NIPT blood test. This has caused so much anxiety for my husband and I as we wait for the results.

    • Based on your combined test, you have a 0.6% chance that it is a true positive and a 99.6% chance that it is a false positive. The NIPT results, however, will trump the combined results. Your experience of heightened anxiety is one many expectant mothers have, but I hope your receiving good support and counseling.

  24. I just turned 32 last week. I’m 13 weeks pregnant and my NT scan at 11 weeks 5 days came back at 4.8 mm and my Progenity results came back with a PPV of 52%. I’m doing CVS this week.. what are the chances that it was a false positive? I’m so scared and heartbroken.

    • Based on Progenity reporting a PPV of 52%, then your chance that it is a false positive is 48%. You could get a more refined calculation by entering your age and the condition screened for into this online calculator. Professional guidelines also recommend that you receive information about the condition tested for. If that condition was Down syndrome, at the Prenatal Resources Tab are the resources recognized by professional organizations.

  25. Rajeswari says:

    My sister is 12 weeks pregnant,she had been tested positive for down syndrome in prenatal test.Her test result was 1:174…,Is this has high risk..,or there any chance that result becomes false?

    • The test result of 1:174 means she has a 0.5% chance that her test result is a true positive, i.e. that her pregnancy actually is positive for Down syndrome, and a 99.5% chance that the test result is a false positive. So, yes, there is a chance that the result is false–in fact, it is far more likely that it is a false positive rather than a true positive.

  26. Jennifer says:

    Thank you for this!! It has helped me to look at it more positively. Since I did not have any early testing done, this is all they have to go on. Send me positive vibes and happy thoughts! I need them to get through the next week or so of waiting 🙂 Thanks again for taking the time to send this reply to me, it means a lot. Congratulations on your healthy baby!!

  27. I had the panorama done with the NT ultrasound at 12 weeks and my ultrasound came back normal, with panorama results low risk >1in 10,000 for all three trisomies and a fetal fraction of 11% . At my 21 week ultrasound the doctor noted one EIF on the babies heart, no other findings. With that, how likely is it that my NIPT was a false negative result and the baby actually has DS? I’m 32 years old.

  28. Your chances that your screen-negative Panorama result is a false-negative is less than 1% (particularly with that relatively high of a fetal fraction). You can find a link to a calculator to see for yourself at this post along with many other helpful links to explain your cfDNA screen result.

  29. karina veras says:

    did your baby end up perfectly healthy or did it perhaps have the t21? i am in the same boat as you and looking for comfort.

  30. Thank you for your quick reply mark! I had a difficult time understanding the data around the test. Does the sensitivity rate of approximately 99.3 account for test samples that were inconclusive that later came back identifying a Down syndrome diagnosis, either at birth or through invasive testing? Or does the sensitivity rate only account for tests that were able to be read As high or low risk? I haven’t found a lot of data of case studies showing people that have had negative results that ended up positive, so that is what prompts the question about the sensitivity of the test. Additionally, I don’t completely understand how the cvs test is considered diagnostic with a higher sensitivity rate when it appears that they are testing the same thing, placental Dna.

  31. The “99.3%” sensitivity means that, according to the lab, if their test tested 100 pregnancies that actually were carrying a child with Down syndrome, their screening test would detect 99.3% of them. Same goes for sensitivity, i.e. if the claimed sensitivity is “99.9%” then, out of 1,000 pregnancies not carrying a child with Down syndrome, their screening test would correctly label 999 as “negative.” While these 99+% are high, when applied to large numbers, it can still result in a false positive of 50% or greater (as the post this comment thread is a part of explains). And, yes, because a CVS tests the same DNA source as cell free DNA, that is why the National Society of Genetic Counselors recognizes it as a limit and advises that an amniocentesis is the diagnostic test with the greatest accuracy for confirming a cfDNA screen, since amnio tests cells actually from the fetus.

  32. Stephanie Dudley says:

    I’m 39 and had the progenity text done. They said that my baby had down syndrome. I go in next week for amno.. 😢

  33. According to the calculator, your screen positive has a 9% chance of being a false positive. According to professional guidelines and several state statutes, you should have received with your screen result this resource that shares information about Down syndrome. I hope the procedure and recovery go well with the amnio.


  1. […] question was prompted by a comment  by Robert Resta on the blog post that I discussed on Tuesday. Resta is the same Genetic Counselor who noted that in this century, most Down syndrome […]

  2. […] as compared to 1st trimester screening has been introduced in Mumbai. [has not been shown more accurate in all populations] It can detect chromosomally linked diseases like Down’s syndrome with a […]

  3. […] but 99% is the detection rate, while the 99% chance of having a child with Down syndrome is the positive predictive value (PPV). It doesn’t help that labs like Sequenom, the maker of Horan’s chosen test, […]

  4. […] Positive predictive value is the computation taken of a mother’s chance for having a child with Down syndrome, based on her age or a first-level screen result, and then applying NIPS sensitivity and specificity rates to that chance. […]

  5. […] but what the screen result’s positive predictive value (PPV) is. This was a concerned raised in 2013 with the way cfDNA screen results were being reported and leading to much confusion on what […]

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