Confusing NIPT / combined test results

[Elle1002]

Hoping for some advice... I had a 99% positive Harmony test for Downs privately then had the combined test afterwards which showed a 1 in 15 chance. I am now waiting for the results of the CVS (should take 3 days) and am confused as to which statistic I should believe as they seem so different...

NT was 1.40 but Free Beta hCG 2.2484 and PAPP-A 0.2975. All other soft markers normal aside from hypoplastic nasal bone.

I would think with these results a Downs diagnosis is highly likely and want to prepare myself but any advice or similar experiences I would be interested to hear.

Hi. I've had a high chance NIPT test for T21 following a >1 in 4 from the combined test. My baby's NT was 5.3mm though- much higher than yours. I'm not having invasive testing and I'm continuing with the pregnancy. From what I understand the NIPT is unlikely to be wrong but it's not 100% so I do hope you're in that small percentage. Sorry you're going through this. I've been going through all sorts of emotions and it's horrible isn't it?

@Elle1002 I am so sorry to hear what you are experiencing. I will PM you

The harmony test would be the most accurate wouldn’t it?

I’m so sorry for the worry you’re going through, it’s horrendous

Are you Indian, Arab, African or mixed race? If so those results could potentially be normal

The combined test will take ethnicity into account in its model, so could explain that, but the harmony test is a DNA test. I don’t see how ethnicity would affect that. The reason it’s not 100% accurate (ie diagnostic) is due to the small chance of mosaic pregnancy

In very simplistic terms, the combined test calculation starts with your age (assuming that older mothers are more likely to have affected baby) and compares the NT and your hormones to the “average” for a matched population (ie taking into account ethnicity/smoking/IVF pregnancy). The more any of your results deviate from “average” (1 MoM) , the more the algorithm assumes the chance is that baby is affected by one of the conditions
NIPT ignores averages and finds fragments of baby’s DNA in the mother’s blood. If there are proportionately more of one chromosome that the others (ie much more of chromosome 21 than the others) it suggests baby has additional of that chromosome.
Therefore NIPT is more accurate.
As PP said there is always the chance of mosaic trisomy or placental confined trisomy, so interpretation must be done by a specialist.
I am happy to discuss results with anyone who is finding it difficult to get clarity. I am absolutely committed to sharing high quality information with women about this type of testing and interpretation of results.

Thank you so much for clearly stating that NIPT is more accurate - I thought that was the case from Googling but the doctor I saw didn’t give me the clearest feedback (and I was very emotional at the time.) I guess I will wait for the results of the CVS but prepare myself for what is expected. It’s just a rollercoaster of emotions right now and not something I had prepared myself for.

I’m so sorry Elle. I’m so glad nanmumandmidwife is on the thread to help

I'm afraid NIPT is likely to be correct.

So sorry you are going through this. I had a tfmr at 18 weeks for Downs plus organ abnormalities. It was a very, very hard time but the right decision in our case.

The ARC-UK helpline is a great source of unbiased support and information.

I just had to look up the meaning of tfmr. So sorry to hear that happened to you SF. Such a difficult time. I think I’m a bit in shock right now. Will check out ARC-UK, thank you

Gosh @Elle1002, it’s awful that you have found yourself here, sending you a big hug. I had a combined result of 1:441 - I’m 34, but my NT was 5.5-6 and no nasal bone absent too. We went straight to a CVS and got the result confirmed that it was a downs pregnancy.

We too chose to terminate and I had a TFMR at 13.5 weeks.

I second the ARC, they are so fantastic, and @Nanmumandmidwife too.

Crossing my fingers everything works out for you, but if you need to ask any questions please don’t hesitate.