What have we learned about the new Down syndrome prenatal test?

Sequenom's updated logo

Sequenom’s updated logo

In 2011, a new prenatal test for Down syndrome entered the market offering earlier, safer, and more accurate results. What have we learned about this new technology since then?

It’s non-invasive prenatal screening, not diagnostic.

On October 17, 2011, Sequenom, a San Diego biotech company, launched MaterniT21, a prenatal test for Down syndrome and other conditions with an extra chromosome. Competitors have since entered the market offering their own brand: Ariosa’s Harmony, Verinata’s verifi, and Natera’s Panorama. These tests promise very high detection rates and very low false negatives based only on a test of the mother’s blood.

When the testing was being developed, it was thought it would be diagnostic. When it came to market, however, it still had false positives and false negatives, rendering it not a diagnostic test, but a screening test. To emphasize this point, the American College of Medical Genetics & Genomics (ACMG) labeled the testing “Non-Invasive Prenatal Screening” or “NIPS.”

Tests placental DNA, not fetal DNA.

At the time of the launch, NIPS was described as testing cell free fetal DNA (cffDNA). It turns out the testing is of DNA from cells in the developing placenta, not the fetus. In 2015, the largest known clinical study of NIPS noted that false positives and false negatives are due to the testing of placental, not fetal, DNA. There is a phenomenon known as “placental mosaicism” where cells in the placenta can have a third copy of the 21st Chromosome, the most common cause for Down syndrome, but the fetus does not have Down syndrome. This is one of the reasons these tests will have false positives and false negatives, because they are not testing DNA from the fetus.

Tests’ accuracy is limited to high-risk populations.

The study Sequenom relied on to take its test to market was of a population with an incidence rate as high as 1-in-8, meaning one out of every eight pregnancies was positive for Down syndrome. This high of a rate does not happen in the natural population. While the chance for Down syndrome increases with the age of the mother, even a 45-year-old mom’s chance of having a child with Down syndrome is 1-in-35. The other testing companies have also reported their accuracy levels in populations already designated as “high-risk,” usually women 35 and older or those who already had a prenatal test showing an increased chance for Down syndrome. In a study of the general population, receiving a “positive” NIPS result meant it had a 45.5% chance of being a true positive, or a greater than 50% chance of being a false positive. Similarly, in 2015, the largest known clinical study reported that the younger the mother, the less accurate a NIPS result was. As a result, the guidelines published by the National Society of Genetic Counselors (NSGC) and the American Congress of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine, recommend NIPS be offered only to women who are already considered “high-risk.” After the 45.5% result in the general population, the Society for Maternal-Fetal Medicine reiterated that NIPS should be offered as a second-tier screen, i.e. to women considered “high risk.”

Insurance coverage is limited to high-risk moms.

Due to the professional recommendations, while NIPS is increasingly being covered by more and more insurance plans, that coverage remains limited to tests performed on mothers considered “high-risk.” As shown in the charts below, this is because the clinical studies have yet to show that NIPS provides reliable results in low-risk moms.

When a “positive” means a 50/50 (or lower) chance.

The professional recommendations are supported by NIPS having a much lower predictive value in low-risk populations.

Positive predictive value (PPV) means how likely a “positive” test result actually means the tested-for condition is present. PPV is the number of true positives divided by the total number of positive tests returned, both true and false positives. When the new test is performed in populations considered low-risk, a positive result can have a PPV of less than 50%.

For example, a 30 year old mother has about a 1-in-1,000 chance of having a child with Down syndrome. At that incidence rate, the chart below shows the number of true and false positives the new tests would report at a detection rate of 99.5% and a specificity rate (the rate of ruling out unaffected pregnancies) of 99.9% for 100,000 30-year old pregnant women, 100 of which would actually be positive for Down syndrome:

Down syndrome pregnancy

Unaffected pregnancy

Test Positive

99.5 (True positive)

100 (False positive)

Test Negative

0.5 (False negative)

99,800 (True Negative)


Therefore, a 30-year old woman receiving a “positive” test result could be in the 99.5 who are actually carrying a child with Down syndrome or the 100 who were not. This gives her a 50/50 chance. With the chance for having a child with Down syndrome tied to a mother’s age, it is more likely that a woman under 30 receiving a “positive” NIPS result is not actually expecting a child with Down syndrome.

Imperceptible reassurance for younger women.

The overwhelming majority of pregnant women are not carrying a child with Down syndrome. Therefore, almost all women considering prenatal testing are not doing so because they expect to receive a positive result. Rather, they are seeking reassurance through a negative result. This is what is promised by NIPS’ low false negative rate. But, for younger mothers, Robert Resta, a genetic counselor and former editor of the Journal of Genetic Counseling, considered that level of reassurance “not exactly a great scientific achievement.”

This is because younger mothers already have close to, if not the same, chance of not having a child with Down syndrome as the test’s ability to screen out those pregnancies that are not affected.

The NIPS labs quote a specificity rate, the ability to rule out those unaffected pregnancies, of 99.9%. But, as the table for Negative Predictive Value (NPV) below shows, mothers under 30 are already at that 99.9% rate based solely on their age:

Figure 3 NPV maternal age

NPV maternal age

Therefore, the high accuracy rate is largely imperceptible in low-risk populations, particularly mothers under the age of 30.

NIPS is not the holy grail of Prenatal Testing.

A former chair of ACOG’s ethics committee recounted her experience of being an older mom—over 40—and expecting her fourth child. She reported how her obstetrician exulted with the new testing, “this is the Holy Grail. It’s what we’ve been waiting for all these years.” This reaction has been common to the new prenatal testing, but it is incorrect, and not even shared by the testing companies themselves.

The notion of a “holy grail” of prenatal testing is a test that can diagnose the fetus without exposing the pregnancy to the risk of miscarriage. Current diagnostic tests—a first-trimester chorionic villus sampling (CVS) or the more commonly performed second-trimester amniocentesis—both have a chance, however slight, of procedure-related miscarriage. This is due to a needle being inserted into the womb. However, these tests remain the only way still to receive a diagnosis, and, pursuant to guidance by the National Society of Genetic Counselors, because CVS tests placental DNA, it can have the same risk of returning a false result, making amniocentesis the more accurate diagnostic test.

Every professional organization’s statement on NIPS makes clear this point: that diagnostic testing is necessary to confirm results and women receiving a NIPS test should be offered diagnostic testing. Put another way, a NIPS result is never truly positive or truly negative. Therefore, because NIPS is still a screening test, and not a diagnostic test, it is not the holy grail of prenatal testing.

But, one of the predictions when Sequenom launched has proven true.

Dramatically fewer invasive diagnostic procedures.

Due to its high rates, it was predicted that mothers would choose to rely on their NIPS results and forego exposing their pregnancies to the risk of miscarriage from diagnostic testing. This is, in fact, what is happening.

Mothers receiving a negative NIPS result are choosing to avoid the needle of diagnostic testing. Those receiving a positive NIPS result who intend to continue their pregnancy similarly are relying on the NIPS result to prepare for having a child with Down syndrome rather than risk miscarriage to know for certain. The testing companies have found that the rate of diagnostic procedures has plummeted following the introduction of NIPS.

The need for educational materials for patients and providers persists.

When Sequenom launched its test, the study it relied upon recognized then that “educational materials for both patients and providers” were needed. Since 2008, in fact, federal law has recognized the need for patients to understand the accuracy of prenatal tests, to receive written materials about the tested-for condition, and to be referred to parent support organizations. In the summer before Sequenom launched, the NSGC and the American Academy of Pediatrics each published guidelines recognizing that patients receiving a positive prenatal test result for Down syndrome should also receive accurate written materials about Down syndrome and the chance to contact fellow parents. Since launching, all of the NIPS laboratories have emphasized their role in providing information to patients.

But, none of them have yet to provide information consistent with federal law and professional guidelines when they deliver a test result.

Instead, patients receive a one-sheeter that only reports the results of their tests. Whether the patient receives written materials or referral to support organizations is dependent upon their health care provider. But, when ACOG surveyed its own members after its guidelines changed to offering all women prenatal testing, less than 3-in-10 said they provided educational materials to their patients.

A mom shared how she received her test result over the phone. She sat in her car in the parking lot crying after hanging up. She wanted more information, but, as she said,

Nobody offered anything. Nobody told me about any resources.

The federal law has gone unfunded and unimplemented by the Department of Health & Human Services. Tired of waiting, Massachusetts, in 2012, then Kentucky in 2013, and then evermore states in each successive year,  passed a law requiring health care providers deliver with each test result for Down syndrome educational materials from the National Center for Prenatal & Postnatal Down Syndrome Resources and referral to the patient’s local parent support organization. The materials from the National Center are the only ones that have been both approved by the NSGC and recognized by the ACMG as resources that patients should receive with a test result. In 2015, the NSGC published a fact sheet for implementing these laws.

The NIPS market was estimated at $1.6 billion this year. Verinata was acquired by Illumnia for $350 million. By 2019, NIPS is expected to be the fastest growing offering of a prenatal testing global market valued at $8.3 billion. Increasingly the cost of testing is being covered by insurance and government health programs. Yet, none of the testing manufacturers are providing the recommended information to accompany their tests and insurance companies are not covering the costs for health care providers to provide this information.

Women are aborting based only on a NIPS result

While suspected, and single case studies being mentioned at conferences, in 2014 an investigative report shocked by sharing how 6 percent of surveyed termination decisions were made based solely on a NIPS result. In response, the Society for Maternal Fetal Medicine issued a statement emphasizing that a NIPS result is never diagnostic:

It is important for providers to remember that cell free DNA is a screening test, and does not have the diagnostic accuracy of amniocentesis.  By its very nature, a screening test does not tell with 100% certainty whether or not a fetus will be affected by a given disorder. Unfortunately, in part because of the high stakes in this very competitive market, the tests are being presented as having >99% accuracy, the same accuracy as is used to describe amniocentesis and CVS.

Links in the quote are to relevant posts on this blog expanding on those subjects, like how “99%” can constitute malpractice.

Yet, in 2015, the largest clinical study of NIPS reported that up to 16% of all terminations were based solely on a NIPS result. The decision to terminate a pregnancy should never be made based on a maybe, but the hyping of NIPS’ accuracy, coupled with the lack of information given to patients, is it any wonder that women are making uninformed, life-changing decisions?

What we’ve learned about NIPS.

Since 2011, much has been revealed about the new prenatal test for Down syndrome. It is not the holy grail of prenatal testing. Rather, it is a screening test of placental–not fetal–DNA, that has been shown to be effective in high-risk populations. NIPS is resulting in fewer invasive diagnostic procedures and is increasingly being covered by insurance. But the need identified when NIPS launched two years ago, and by federal law five years ago, and by laws in an ever growing number of states, for patients to receive educational materials about Down syndrome from their health care providers and from the testing companies remains, despite these resources being available and the laboratories being part of a billion-dollar industry.

This post was updated on June 24, 2015.


  1. My wife and I are in our mid twenties. We are both healthy and no family history of Down syndrome. We took this blood test at 11 weeks and came back “99%” for T21. My wife is extremely upset and I am in disbelief. I don’t understand this at all….I’ve read so many of your articles. The mid wife couldn’t even explain this test whatsoever to us. Simply handed us a sheet of paper and even eluded to abortion…..based on all your articles. This 99% is not a true number because my wife is in her twenties and not considered high risk….this is so confusioning.

    • You are correct. The tests do not report a 99% chance of your child having Down syndrome, particularly given that your wife is in her twenties. Instead, she has a more than 50% chance that the test is a false positive. I regret you are not receiving accurate information or support. I hope what you’ve read here has been helpful.

    • Frank, Please let us know when you do a diagnostic test, such as a amnio, as to what the real tests tells you and your wife. I just had the Harmony test and it told us that we are < 1/10,000 of having a child with DS, TRisomy 13 and 18, which is a very low risk of having a child with DS, TRI 13 and 18. I am 43 years old, so I am in the high risk group so I hope this test screened me accurately, but I am still considering having an amnio done, even though the screening test said my baby is at low risk. We are having a level two ultrasound the beginning of December, which should reveal more information if anything is wrong?

      • The later amniocentesis is done, the larger the fetus and the lower the risk of miscarriage. Thats one way to lower the risk of amnio, but get an accurate result on which to act. Judy Slome Cohain, midwife

    • Can you give us an update on your wife pregnancy? Thank you!

  2. I am 40. 16 weeks pregnant NIPT came back high risk. No markers on scan. Did amnio 2 days ago and waiting for results. I cant eat or sleep. Don’t really see a lot of false positives at my age.

    • It depends on what your NIPT result came back high risk for. In the case of Down syndrome, you’re correct: the rate of false positives is around 10% at your age, i.e. you have a 1-in-10 chance that the result is a false positive. However, in the case of the other trisomies (18 or 13) or any other chromosomal condition tested-for (e.g. microdeletions or sex chromosome aneuploidies), the chances are higher that the NIPT result is a false positive. No matter the condition, your higher anxiety is one many expectant mothers experience with a screen result. To address these concerns, ACOG, ACMG, and NSGC all recommend that you receive genetic counseling and be provided written materials, with all organizations recognizing Lettercase’s “Understanding a Down Syndrome Diagnosis” as the written resource for expectant mothers. You can find that booklet and other recommended resources at this tab. I hope the information is helpful.

      • Thx for your reply. We received the results this afternoon, and it is trisomy 21. Is amnio always correct?

        • Amnio is considered diagnostic. While false positives have occurred, an amnio is the gold standard of prenatal diagnostic testing. If you did not receive the recommended materials linked to in my earlier reply, I hope you will access them and get good support.

  3. Hi there,

    I’m 36 years old, and just received a positive for Down’s syndrome from the harmony test. I know I’m grasping here, but what are the chances of a false positive at my age. Our first trimester screening was 1:35.

    • Based on your age, you have an 18% chance that your screen result is a false positive. Based on your first trimester screening result, you have a 3% chance that your Harmony result is a false positive. You can use the calculator linked at this post to calculate for yourself. Professional guidelines recommend (and laws in certain states) require patients to receive written information and referral to support resources with a screen positive result. You can find these recommended resources at this tab on this website.

      • The same thing just happened to me. I’m 35. Ended up aborting my baby after cvs confirmed downs. I’m so sorry. It’s a really hard thing to deal with. But I believe I made the right decision for me and my other children. Good luck to you.

        • I am 37 and pregnant for the 5th time. I have 3 healthy children and terminated a pregnancy at 13 weeks that was trisomy 21, detected on NIPS and confirmed with CVS. I am 12 weeks now and just got the negative results on the NIPS but am wondering if I should still do invasive testing. The nuchal screen and first trimester screen were normal as well. My OB did not offer much guidance and only said if I need that for reassurance to let her know and we can schedule it. I don’t know if it is worth the risk of miscarriage to get a more definitive answer. We would terminate if there are chromosomal abnormalities. Do you have any insight on this?

          • Having had a previous pregnancy positive for Down syndrome, you had roughly a baseline chance of 1-in-100 for having another child with Down syndrome. Based on the negative predictive value calculator available at this site, with that 1% prevalence chance, the odds that your screen-negative is a false negative is less than 1%. The only way to know for certain is with an amnio, but you have a greater than 99% chance that your screen negative is a true negative.

  4. Hi, I am 39 years old, 18 weeks of pregnancy. I receive a call from my Dr, the “preliminary” results of my NIPS test (Panorama) was positive “91%” for T21. I have an appointment for the amnio on Tuesday. I am confused, if you can help me to understand what the preliminary results means (why preliminary and no final?) and the 91% what exactly means. Thanks for your help.

    • I don’t understand the “preliminary” either–NIPS results are what they are, not preliminary and then final. The “91%” would be the positive predictive value for your NIPS result, so I think the doctor may have just misspoken.

  5. I am 29 years old and two weeks ago we found out our little girls have an AV Canal defect. The doctor then asked us to take a Harmony test because of the number of children with Downs that have AV canal defects. The doctor called this past Monday and informed us that our baby would be born with Downs based on the Harmony results, didn’t say anything about the Amnio or that the harmony is a screening. I am not trying to live in denial, but I truly don’t believe she has downs. Her ultrasounds look great and there are no soft markers for Downs other than the heart issue. My husband and I don’t want to do the amnio because of the heart defect, we just don’t want to complicate things. What do you think the chances of her having downs are?

    • Aside from offering you the cfDNA screening test Harmony after an ultrasound marker associated with Down syndrome, your doctor has not followed the professional guidelines for prenatal testing. Based on your age, a screen-positive Harmony result means you have a 58% chance that your child has Down syndrome and a 42% chance that your result is a false positive. This may be revised based on the AV canal defect, which you should discuss with a genetic counselor. You also should have received written resources that are available at the Prenatal Resources tab on this site. Click this link for links to how you can calculate your chances and a fact sheet your provider should receive.

  6. I am 27 years old and after the 12 week screening we recieved a 1 in 5 chance of T21. We decided to take the NIPS and it came back positive. We are not going to do an invasive testing as we will continue the pregnancy no matter what. I have come to terms with the fact our daughter probably will have down syndrome but am still unsure with the accuracy of these screenings. I am curious on your thoughts. Thank you.

  7. I am 39 years old and currently 13 weeks pregnant. I did the MaterniT21 test when I hit 10 weeks, and my doctor called to tell me that we “…tested positive for Trisomy 18”. He referred me to a Maternal Fetal Medicine specialist who I saw right at 12 weeks. They did a level 2 ultrasound to look for markers, and didn’t see a single one. Baby appears completely fine at the moment, although he did explain that markers could show up in a later ultrasound. He recommended an amnio, which we will do when I hit 15 weeks, along with another level 2 ultrasound. I used the calculator that you provided a link to, and it actually says there’s a 31% chance that it could be a false positive, but that was at 16 weeks gestation. My question is, how much would that change if I did the MaterniT21 test at 10 weeks? And secondly, do you feel that having a completely clear ultrasound improves our odds even more? Or does that not really matter when determining odds?

    • Screening tests like MaterniT21 increase in accuracy the later they are performed in a pregnancy, which means they are less accurate the earlier they are performed in pregnancy. This means your odds are probably higher than 31% that the test result is a false positive. Per your MFM, the physical characteristics associated with Trisomy 18 are also more likely to be seen later in the pregnancy, so the clear ultrasound at 12 weeks may not have that much significance.

      • Hi Mark,

        I am 33 years old and 13 weeks pregnant with our first child. I had the Panorama and the NT test plus blood work done and received a call today from my OB, who let me know that the Panorama results came back negative, but the combined NT plus blood work indicated a 1:49 chance for chromosomal abberations. She recommended to make an appointment with a genetic counselor and to consider CVS. As I was on my commute I did not get further details e.g. as for which trisomy the risk was elevated.

        From what I understand the chances to get a false negative NIPT result are <1%. How likely is it that the NT plus blood work result is a false "positive"? What are the real chances? I would like to avoid any invasive diagnostic method, but the final result might influence our decisions about continuing the pregnancy.

        Thanks for providing all this statistical information to help getting a better feeling for true probabilities of prenatal screening results!

        • It depends on what “chromosomal abberations” were suggested by the NT result. Panorama is recognized for testing for Trisomies 21, 18, and 13, and for detecting the sex of the fetus. If the NT result was for the three major trisomies, then Panorama trumps the NT result. If the chromosomal abberations are for other conditions besides Trisomy 21, 18, or 13, then you can discuss that with your genetic counselor. It sounds like, though, you’ve got a false positive NT-result and the negative from Panorama could be relied upon.

          • Thanks for your reply. Today I had another talk on the phone with my OB and was a little better prepared than 2 days ago. It seems as if my 1:49 risk for Down was only based on the blood serum results. The NT was fine. No indication for trisomy 18 and 13 either. And it seems as if even the PAPP-A and b-hCG levels were in a normal range. Only the AFP level was low. Which made me wonder because I read that the AFP is usually only screenee after the 14th week when the blood level begins to increase and I had my blood drawn during week 12. I also read that the AFP levels are naturally somewhat lower for Asian women (I’m half-korean). Overall with the negative panorama test I am pretty relieved right now. But I’m furious on the other hand that the AFP levels were taken into account at all for my first semester screen and caused so much worry.

          • I’m not sure either why AFP was included since you are correct that that is a second trimester screen.

  8. Hi- I’m 30, no family history for myself or husband, both very healthy, have a heathy 15 mo at home, both pregnancies “textbook” perfect, no trouble conceiving. Progenity came back positive for T21. I just can’t believe it to be true. Went to specialist today and genetic counselor explained we actually have a higher chance for a false positive than 1% bc we are in a low risk group. Have amnio scheduled for when I turn 16w (next week). Any feedback or hope to offer? Im so excited and hopeful after our appointment today hearing there’s a chance…. But trying to still be prepared for the worst.

    • I meant *lower* chance….

    • See the links in this post about why your cell-free DNA test is never truly “positive” and the calculator where you can calculate your own positive predictive value, i.e. the chance that your test is a true positive. At the end is a link to resources about Down syndrome to learn more about what a life with Down syndrome can be like. I hope all of this information provides hope.

      • Thank you for your response. You website has been so helpful to me during this whirlwind of the last 48 hours since finding out.

  9. I am totally confused and perhaps I am simply a little stressed… My wife is 34 and currently 12 weeks pregnant. Our Harmony test which came back positive for Trisomy 21 was performed when she was 10 and a half weeks pregnant. Having some serous issues sorting out the calculator… any guidance would be appreciated.. Thank you so much.

  10. Nicholas Hill says:

    My wife is 33 and we recently performed the “Informed Pregnancy Screen” test from Counsyl. The results came back at 52% PPV for Down, which seems at odds with the calculator which gives a 75% PPV. What might be driving the difference, and hoping the 52% is the right number to look at here…

    • If Counsyl is reporting 52% when the calculator says 75%, I’d rely on Counsyl–it’s a statement against their interest to report a lower PPV, making it more reliable. Perhaps, for whatever reason, the sensitivity and specificity of the Counsyl test was not as high as the default settings in the calculator. You could have your provider follow up with Counsyl (and your provider may learn something as well about the accuracy of the screening test being offered to patients).

      • Nicholas Hill says:

        Thanks Mark. I did use the specificity and sensitivity parameters provided straight from Counsyl in the calculator. However, maybe there are other parameters they use as well? For example, we heard we are in a lower risk ethnicity group for Down, so perhaps they are factoring in those as well.

        Also was curious if the test result was binary (high risk, low risk), and then that is adjusted based on age and other demographic factors to calculate PPV? Or does the rest provide a range of results that provide the level of risk?

        In any case, we are scheduled for CVS tomorrow.

  11. I am 39 years old and 12 week pregnant. I am waiting for my NIPT test results. Can it happen that is would be false positive because I have Factor II or G20210A mutation?

    • I’m not sure about that specific situation. As a screening test, it most certainly can have false positives. You may want to ask a genetic counselor, medical geneticist, or the NIPT lab about your specific case.

  12. Hi Mark, I am 35yrs old and had a NIPS Test @ 11wks that came back as High Positive.
    Question: Does the calculation take into account a low NT (1.5) & the presence of a Nasal Bone as part of the Ultrasound?
    Based on my age and results. I have it estimated as a false positive of 80/20%. (Using your calculator) Thanking You…

    • Had you received an NT-combined screen result, then that could’ve been factored with your NIPS screen. If you just have an NT-alone result (i.e. without the serum screening combined with the NT), then that, as well as the nasal bone, are considered “soft markers” and not factored in with your NIPS result. This online resource is recommended for accompanying a NIPS result positive for Down syndrome.

  13. Devi Palanivelu says:

    Hi Mark, I’m a 40 year old pregnant with mono/di twins. My MT21 test came back negative but my combined NT and blood work put me at a risk for DS at 1:16. The NT for both were within normal range (1.6mm and 2.2mm) but the Papp-A was decreased at 0.3MoM. Everyone is saying that the risk looks high but not suggesting that we definitely consider CVS or Amnio. Can we rely on the MT21 and defer the invasive test in this situation? Thank you.

    • The studies on twins are few due to twins being rarer (I, coincidentally, am a twin). Typically, though, the MT21 result trumps conventional screening like combined NT for conditions like Down syndrome. I want to say that the NT is more indicative of DS than the Papp-A, but I can’t say that for certain–something for you to confirm with your provider. All this being said, the chance of a false negative MT21 is very low and why many women rely on MT21 to avoid the risk of miscarriage associated with amnio.

  14. Mark,

    I am 29yo and will turn 30 3 months before my due date. I was offered MaterniT21 as a better option for screening compared to traditional screenings even though I wasn’t a high-risk like you have mentioned. We said yes to the test because our genetic counselor said it is more accurate and an added bonus would be knowing baby’s gender. I found out 2 days ago I came back positive for Down’s at 59% PPV! I was confused because with my son the results were more like a probability(it was i in 9999), so when I asked my counselor she said this result can be translated to more than 1 in 2! We are heart broken and went in for CVS following day and waiting for the results. In a follow-up conversation the counselor said the CVS could be incorrect as well because parts of your placenta may have the extra 21 and parts may not! Which means MaterntiT 21 is not a false positive after all! I am devastated to hear this because she is basically saying even if your CVS comes back negative, it may be incorrect because MaterniT21 showed a very high probability for me. The NT score was normal so I asked her if she could recalculate my probability taking that into account and she said if she did that my numbers may go way down and that may give me a false hope! I am so lost and terrified.

    • Your GC is correct regarding your chances for your test result being a true positive. She is further correct that the CVS could be incorrect. As for the NT, that alone is not recognized as a valid screen so it should not result in a recalculation by itself. All this being said, appreciate that you have a 41% chance of having a false positive and, if you care to learn more about Down syndrome, you can view this on-line resource recommended by all major medical organizations for expectant mothers.

  15. Mark,

    I really hope you can help me shed some light on this.
    I just received my NIPS results (Harmony Test) and the test came out as High Risk (with 99% detection rate) on Downs Syndrome. What is really confusing is that I also received my NT/blood test results which came back “Low Risk” as 1:4500. Both me and my partner are 30 years old.
    Any chances this is a false positive? How is possible to receive two results which go in complete opposite directions?

    I will for sure do the Amnio but have to wait 2 weeks – and I will keep you informed on the results.I am reading that CVS in this case is not recommended because it looks at placental DNA (same as the Harmony) vs. the Amnio looks at fetal DNA therefore is more accurate.

    Kindest regards and thank you so much in advance.

    • The two screens test different material to report their results. NT-combined has more false positives and false negatives than tests like Harmony. Current recommendations are that a Harmony-type test takes precedence over whatever the conventional screen results report for the limited conditions tested for by Harmony-type tests. Based on your age and your Harmony result, the on-line PPV calculator linked in this post reports a 40% chance that your test result is a false positive. You are correct regarding CVS vs. amnio. Please review this post, the fact sheets linked in it and the resources linked at the end.

  16. cari geiss says:

    Hi I am 28 years old and 11.5 weeks pregnant. I had an NT scan that came back as 4mm. I chose to do the NIPT, but after reading this I am worried thst it will not be accirate. Do the statistics you provided on the site apply to me as well? Or are the different because of my NT scan?

    • An NT measurement, by itself, is not a recognized screen for genetic conditions. When it is combined with analysis of a maternal blood sample, then it is a recognized screen. Regardless, cell free DNA screening (AKA NIPT) trumps conventional screening like NT-combined for the limited conditions cfDNA screening tests for (T21, 18, 13). You can learn more about cfDNA screening and what your results mean at this post and the links therein.


  1. […] Update: Since NIPT launched two years ago, much as been learned about what it is testing for, the level of its accuracy, with the laboratories emphasizing it remains a screening test requiring diagnostic testing to confirm NIPT results. These lessons learned since NIPT’s launch are collected in this post here. […]

  2. […] day in and day out, it remains one of the top visited posts. I have updated it with a link to the lessons learned about NIPS in the two years since it […]

  3. […] from an Iviomics press release about its version of NIPS, which it calls NACE. If only Roy had read this collection of what we’ve learned about non-invasive prenatal screening, including its limitations, these […]

  4. […] blood circulation” and that it is “extremely accurate;” both contrary to the lessons learned since non-invasive prenatal screening was […]

  5. […] at his blog Down Syndrome Prenatal Testing offers a very good explanation of the statistics in this post.  Here is another more general article aimed at explaining the confusing statistics behind medical […]

  6. - DownBaba says:

    […] tartottak, de azóta többen felhívták a figyelmet a forgalmazók túlzó állításaira és a statisztikai adatok félreérthetőségére. A figyelmeztetések legfőbb tanulsága, hogy a terhesség esetleges megszakítása előtt […]

  7. […] vértesztek széles körű elterjedésének pozitív hatása, hogy csökkent a fölösleges invazív beavatkozások száma. Nem jó üzlet, ha cserébe emelkedik a fölösleges abortuszoké. Sokat segítene ebben, ha a […]

  8. […] Update: For more lessons learned about NIPT (including why it’s NIPS) click here. […]

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