Is a screening for Down's syndrome ...

[KeepOnPloddingOn]

Generally correct? I know occasionally there can be blips and false positives ... But generally is a high result a positive? I have a 1:27 chance of dc having downs. I have read conflicting info, but some say that getting such a high result generally suggests ds is inevitable - as the screenings are not 100% and a very high result should be taken as a highly likely.

I know this may sound confusing sorry, I am no expert on all this- I have been researching lots and as there are no answers as to why some Get such high results if baby doesn't have downs. So I am starting to believe it means in most cases a very high result such as mine is a 'more than likely' ...

For me it was my bloods giving me this high positive. The nt was 2.10- normal. I am mid twenties.

A result of 1:150 or less is considered high risk by the way. I think if I had a 1:100 it would be different - but our screening was relatively very high ...
Aibu to believe that thiS 1:27 Is not a diagnostic, but a pretty cert dc will have downs....? Any feedback would be appreciated.

The term positive is used in the combined test to refer to high risk cases, i.e. higher than 1;250. These are usually referred for amnio, as opposed to negative ones where the risk of MC from the amnio is felt to outweigh the risk of having a baby with Down's Syndrome. The combined test screening is set up to avoid unnecessary amnios which could result in MCs of healthy foetuses.

A false positive in this sense is a combined test of apparent high risk which is wrong, not in that the risk does not actualize but in that the risk was miscalculated. So a false positive is not the right term for a 1:27 risk where it turns out the baby does not have Down's Syndrome, but rather for a case where the 1:27 is not the right statistical risk, it should have been much lower.

That is my understanding at least, but I stand to be corrected if it's completely wrong.

Booboo, how do they work out that the wrong statistical risk has been given to someone, given that it is exactly that, a risk rating not an absolute outcome?

Well I never got my cvs :( placenta was too far back. Now have to wait until I am 15 weeks for amnio. :'(

May so harmony but nearest place is 2 hours away! Plus it seems they just give a high risk / low risk result ?

Oh, poor you. The waiting is hellish. How many weeks are you now - how long do you have to wait?

I had amnio and the procedure itself was fine.

I get the impression that the Harmony is very accurate. A small amount of your baby's DNA in the form of chromosomes get into your blood. They would normally expect the same proportion of each chromosome to be in your blood. But if your baby has a trisomy then they will have proportionately more of that chromosome in your blood than the others. So it is measuring the actual chromosomes. It has a low false positive rate. It doesn't test for other chromosomal abnormalities (which cvs or amnio can), but it is non-invasive. It takes 2 weeks to get the results.

KeepOn - How did you already have your triple blood test & got its results if you are not yet 15 weeks pregnant?

Triple blood test is done between 15-18 weeks.

Before that, you have nuchal test at 11-14 weeks.

I will phone and enquire for harmony tomorrow. On the web site I read you just get a result back in the form of high risk or low risk? I'll need to check they actually tell you 100% before I commit to it. If we even do. It costs a bomb and is miles away for us.

Côte- I had 12 week scan and the blood test on same day? I was told I was 11+3. I recieved my results next day...

Cote I think you need to check your facts before you least me with unhelpful questions (yet again)

I havnt read through the thread but your last post OP struck me. You had the test done at 11+3 ?! Are you sure because the test should not be performed until 11+5. I know this is only two days but it does affect results.
(I know this as I am a green flag sonographer for NT scans)

Poppie - what!?! Yes the dated me at 11 + 4 (sorry it was 4 not 3) I thought I was a week ahead.

Are you sure!? Surely they would realise this themselves?

My nichal fold was fine though. It was my bloods that flagged up as hcg beta was high and papp- a low ...

Check my facts?

Triple test is done between 15-20 weeks of gestation in the US, between 15-20 weeks in Canada, Netdoctor.co.uk says the triple test is a blood test carried out at around 16 weeks. In any case, it is most accurate when performed between the 16th and 18th weeks of your pregnancy.

Hence my earlier confusion. Is it done much earlier in the UK? That is not ideal if the aim is accuracy (and it should be).

The company that offers the Harmony test has info here.

Are you sure that you have found your nearest Harmony test centre? I was surprised to find someone offering it really near me.

If you had the blood test at 11+3, that was the double test which has significantly lower detection rate and reliability than the triple test.

If you are worried about the amnio, it might be an idea to first have a triple test at 15 weeks and see what its results say.

I think the later blood test in the UK is the quadruple test here

Sorry cote I didn't realise you were referring to American ways....probably explains a lot of the confusion we have had. My mistake on the blood test front though- it was a double test i had.

Pico- yea I have checked ! Boo :/

Pico- as for the quadrupole blood test, I shall have a gander now. Ta.

As I said, the double test is far less reliable than the triple test. I can only imagine that it is being done because of cost concerns - one visit for nuchal test & blood test rather than two visits.

Côte - yes money is the issue as always.

Cost and accuracy are issues, but so too is earlier detection. The links above suggest that the combined test is more accurate and has a lower false screen positive rate than the quadruple test, though a combination of both might be even more accurate.