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.

kim - Are you trying to confuse OP further?

Antenatal blood tests don't give a positive or negative result. All that you have written there is completely irrelevant to a result like OP's 1:27.

Your wiki link looks interesting btw!

So approximately 5% of pregnant women get told that they are high risk, but turn out not to have a foetus with DS? That still doesn't sound right to me. I just don't think that 1/20 women is given a "high-risk" diagnosis.

Me (and I think Pico?) were in fact asking about it in relation to a 1:x result and not in relation to a positive / negative result.

"you don't get a positive result in medicine anyway if you do blood tests"

Of course you do - when you test for a pathogen like HIV, for example.

"False positive" is a meaningless term when applied to a test that gives no positive or negative results.

I agree with Cote - but the information that is out there is very confusing.

I think the difference is about how specific it is - to use the concept you talked about earlier Kim. So a lot of tests where a lay person would understand that positive = positive are very specific. The screening test is very unspecific because the markers are so frequently incidental. No one would understand a 1:x as "positive" rather - you happen to have funny hormone levels / high nuchal measurement etc - this may indicate x y z.

I am really surprised that 5% of pregnancies is diagnosed as (false) "high-risk". It just doesn't match my experience in RL, though I would concede that people may not talk about their experiences openly.

Well because people who have a high risk screening result would not understand that as a "positive" result - (because they are presented with it in a risk based format) - it is meaningless and confusing for them for anyone to then talk about false positives, because (I think) that is implicit in the risk you are given. It would be like saying to a person with 1:27 - you have tested positive however there is a 96% false positive rate. Or someone with a background risk of 1:400 just based on them being over 35 -you have tested positive without even having the screening! but there is a 99.9...% false positive rate.

Compare that to the harmony test for downs when you are only told negative / positive, when in fact it is based on a risk of more or less than 1:10k. Harmony is much more specific though as they are counting the chromosomes in your blood to see if the baby has an extra chromosome.

Tbh Pico I don't think it is that surprising. Once you are over 35 your background risk of downs etc goes to 1:350. That's not wildly off the "high risk" categorisation - 1:150 in my hospital, 1:250 in others. And that's without any other indicators.

Table here

But no one in my RL experience has ever said that they came out as high risk. Am I unusual in that?

And the point of the screening test, in part, is to be able to move people away from their baseline risk towards either a lower or higher risk diagnosis.

Of course I think the words "high risk" are questionable - since when is a 1 in 150 chance a high risk of anything? Similarly when I got my screening results I was told it was "bad news". A really terrible choice of words that really affected the way I saw things. "Bad news" was a 1:37 chance. I think if they had said everything looks good but we do just want to check out this result a bit more closely, for example, I would have felt very differently about the whole thing.