Can amnio be different from NIPT results for T21?

[Chyrsalis2017]

I am almost 16 weeks into my second pregnancy and have received the shocking news from NIPT (harmony) test last week - came back 99% positive for DS. I am still in shock and devastated, cannot believe this is really happening. We decided to go for amniocentesis, despite the risks, and I still have three days to wait for the amnio results to come back. Has anyone had a false positive with NIPT for Down's syndrome and negative results coming back from amnio? I know the harmony test is fairly accurate for T21, but was wondering if anyone at all had a different experience?

I'm sorry you are going through this.

We were told that the false postive rate was 0.1%. So for every 1000 people given a positive result, one person is told wrongly. With the number of people taking the test, there will be many stories of false positives on-line.

The amniocentesis will see whether the trisomy is affecting the foetus, not just the placenta. It will also make sure that your cells are not affecting the result (some people have a small number of cells with extra chromosomes without having any symptoms).

Many posters suggest contacting ARC for help and guidance.

I'm so sorry this is happening to you. I know how hard it is when the Nipt comes back with a result you weren't expecting and certainly weren't hoping for.
The short answer is yes. It can be. There is something called confined placental mosaicism whereby the placenta and the foetus have developed different cells and it's only the placenta which is affected by the cells with extra chromosomes. You've already taken the only test which can tell you without a doubt whether your baby is affected. NIPT takes from placental free DNA which is in your blood and this could be different.
I really really hope it works out well for you and wish that the time you're waiting for results passes quickly. We are here to lean on should you need us. Definitely give the Arc a call - they're amazing and have so much experience and can talk you through it.
Good luck x

I am so sorry that this is happening to you. I had a high risk result for t21 in January on the NIPT. I googled obsessively looking for every bit of hope that it could be wrong.

It is true that placenta mosaicing can give a false reading (although it is not as straight forward as just a mistake) but it is highly unusual. The hospital I went to for my invasive testing is a lead centre for the IONA trial and they had never seen it.

It is also true that for a very small percentage of women there is a false result but this tends to be for young women (unsure of your age) and more often for t18 or t13. Again my hospital had never seen it.

I am so sorry to be so negative but my hospital was very clear that I should not have false hope of a false result. Unfortunately I would therefore prepare yourself that the amino will also show t21 though I pray for you it does not.

Whatever you decide to do I suggest you contact ARC who were very kind during an awful time. I also got lots of support on here.

If you do not proceed with the pregnancy (mine did not proceed) and you want to try again - or you do and want a third - I would also recommend taking up the appointment with the Geneticist that they will hopefully offer you. I found it very helpful.

Big hug

From my reading last pregnancy, if you are generally low risk for t21 (ie age, genetic links etc) there is a 50:50 chance of a normal amino after a high risk nipt. If you are high risk (esp over 40 yo) there is a much lower chance of a negative amino.
Big hug and everything crossed for a normal result for you x

Many thanks for your support and responses. Gurraun, I had a similar message from the doctor that did the amnio - that for T21 she has never seen the amnio results come back different. And my case was, unfortunately, no different; the amnio confirmed that baby had DS. I had a surgical termination last week and still feeling very emotional about this; it was a very much wanted pregnancy and now I have very conflicting emotions about this - sometimes I feel like I want another pregnancy right this moment and then other times I feel so scared that this experience will repeat itself (or something else goes wrong) that I don't ever want to even try again. I guess this will take time to heal, emotionally and physically, it has been a very difficult experience and I need to somehow move on...

I am so sorry - I have only just seen this. It is such an awful experience and I am so sorry you are going through this.

I am now 5 months on and heading rapidly towards what would be my due date and still feel all of the emotions you describe but it does get better with time. I am now certain I'd like to try again but DH not so sure (i already have 2 DS so a third was always an indulgence). This is a big movement from the early weeks when that was the most terrifying prospect ever (still is scary).

I'd recommend some counselling- I had some and not sure how much good it did but it was good to just let it all out a bit - my friends and family have been amazing but it is different speaking to someone completely impartial.

Thinking of you at this awful time x

Im 11w. I did nipt test and its positive but they put my due date wrong 7 days Will it affects the result? Tia

Hi Bianca. You might be better starting your own thread on this but I don't think the dating being wrong will give you a wrong result from the NIPT. They are looking at fetal DNA present in your blood stream so false positives tend to due to placenta mosiacism and are very rare as mentioned above. Have you chatted to your midwife or whoever carried out the test?

Thank you for your reply. Will see Dr tomorrow.

Hi Bianca, hopefully your doctor will give you unbiased information and sources of info about all of DS rather than just the medical possibilities. positiveaboutdownsyndrome.co.uk/ is a website with no political or religious connection, just people telling their truths.