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.

Madrigals - What does "95% accurate" mean in a test that only gives results such as 1:750? (See earlier discussion on this thread)

I don't think it is controversial to say that the triple blood test is more accurate than the double test, simply because it checks one more hormone. Both are weighed with nuchal test results.

Looking at the NHS screening programme recommendations, there was also the risk of women failing to attend both appointments which wouldn't allow reliable screening. This is really important when tests can only be done in a set window of time and getting overstretched MW to chase up non-attenders in time was deemed to be problematic.

plodding - harmony is very accurate. I think it is basically a yes / no result - do you have the extra chromosome in your blood or not? However there is a thing that can cause a false result - it is something to do with the placenta having two different groups of genes (sorry can't remember more than that). It is very unlikely and I think that is why instead of being told you have a negative result you are told you are highly unlikely to have the condition.

I hope that doesn't confuse you more! As I know that's the last thing you want.

More likely issue is you do harmony and after waiting two weeks for results you are told there was not enough chromosome in your blood to run the test properly. I was warned this might happen and have heard of it happening to people.

But - if you can find the money I would strongly recommend doing harmony even with a two week wait. Far and away the most likely result is "highly unlikely to have downs" and then you can skip the invasive test.

And sorry you never got your test.... must have been a bit of a blow

HaveYou - I think the two sets of genes thing is mosaicism. As the growing embryo develops by cells splitting into two, you can get an 'error' such as a trisomy, where one of the daughter cells gets an extra copy of a chromosome. But because this happened when there were some cells without trisomy, the foetus will end up with a mixture of cells with trisomy and cells without. I guess that when the cells without are in the placenta, then you would get a negative result, but the foetus would be effected by the trisomy. I think this must be quite rare, but I'm no expert.

That's the one. Makes a lot more sense now than it did when the midwife was trying to explain it to us.....

Hope you sleep well OP. Very soon this will all be in the past You have every reason to feel positive.

Thanks have I am going to phone them today to enquire if it is a definitive answer. Trouble is someone said to me it is only a definitive answer for one of the 3 major trisomys - so is that the threw types of downs , or the do hey mean you get a positive for having downs / Edwards / Patue?

Would the blood test detect the type of downs? I imagine they would have to tell you otherwise you would need further invasive resting to establish which chromosomal abnormality it is? Then there would be little point in having it altogether...

I'll keep you posted what the clinic say. Part of me wishes I had just payed for it initially now. However, being young I honestly never really considered downs. Naive.

I know it is trite to say and impossible to do but try not to worry. Ignore what you can't do anything about until you can as you will drive yourself nuts.

I was told my baby may have Edwards Syndrome and I posted and helpful posters told me to ring the Ante-natal results helpline and they were very kind.

I had immediately made the decision I would refuse an amnio and was having the baby regardless. This did not go down well with the hospital but I didn't care. He was my baby and it was nothing to do with them. I worried all through the pregnancy but as I had decided to have the baby anyway, and already loved him and felt very protective of him, I just took it a day at a time.

The hospital were completely wrong and I would have lost a perfectly helpful child if I had given in to their pressure.

Unless it is an amnio nothing is certain so try not to worry and speak to the hospital to see if you can get anymore information.

pico2 that is a very interesting question. I don't know the answer but here is my speculation. I run it past DP who works in statistics (but not medicine):

There are two possibilities. Either a technical error, e.g. An ultrasound machine error or a lab machine error. Or they run two tests at the same time to compare the NT measurements of two technicians, the lab analysis of two laboratories and the statistical analysis of two statisticians. If they end up with different results one is making a mistake and uncovering what it is would tell you whether you have a false positive or a false negative.

DP also suggested that when dealing with unlikely results false positives are identified differently from false negatives, but he lost me with the statistics so I can't explain the idea!

Midwife told me today that my Nuchal fold measurement is fine on its own, but when my age is taken into account it is part of the high risk result I got. The other midwife said it was my bloods that made me high risk. I was unaware my age and the nichal fold could be related...

Basically I didn't realise my Nuchal fold measurment was in anyway part of the high risk. I know they mix all three together to get a final screen result - bit I thought as my Nuchal fold was normal range (2.1) it couldn't have had anything to so with the end result iyswim? I know what ia mean but I realise I am not explaining self well ...

Well there's normal and normal! So my nuchal fold measurement was 90th centile. Stil therefore in the "normal range" but higher than most people's so still contributed to my high screening result.

Sorry if I missed it but have you decided what testing to do?

I hope the talk to the midwife helped answer other questions. Try to step back a bit and wait for whatever test results there are or else you're going to drive yourself demented trying to understand / quantify what is just an unknown with an awful lot of statistics and uncertainties.

Good luck and remember - the overwhelming likelihood is that everything will be fine!

my dd had a 1:2 chance! she is a really healthy 2 yo now no problems at all

*dont know if the ratio 1:2 is right but it was a 50 percent chance

keep on your final result is a statistical analysis of three things:
First your age
Then this is recalculated based on the NT measurement
Then a final result is arrived at from recalculating with the results of the blood test

Thanks everyone. Have - I must be like you in that my measurement Is ok- but high side of ok...

OP have you looked at the long running harmony thread on here? I don't think they can give you 100% result but it's supposed to be near as. There are also a number of reasons why your blood test results might be skewed that aren't anything to do with a genetic problem and your nuchal doesn't sound especially worrying. Also I think it's helpful to think that whatever the situation with your baby it's been as it is for many weeks now it's just when you find out - the baby is as it is.

Thanks tinkey I have looked into the harmony and at this stage of the game I have decided against it for various reasons- one being I would need the amnio anyway of the baby does have downs- also the nearest place to get it is 2 hours away.

keepon the Harmony test does still have the advantage of not having any risks whereas the amino carries a risk of miscarriage.

Boo the risk of miscarriage is 0.5 (many say in 500)

Plus the harmony is not 100% for less chromosomal abnormalities :)

I think that I would have an amnio/cvs if my nuchal scan showed high risk, even if the Harmony didn't (subject to the advice I was given by HCPs). The invasive tests can look for a wider range of genetic abnormalities, Harmony only looks at 3 and isn't as unequivocal on at least one of them. I'm looking to the Harmony to possibly pick up on "false negatives" from the nuchal/combined screening, rather than replace it.

Interesting keepon, the studies I have seen put the risk of MC from amino at between 1:100 and 1:250.

pico2 I recently did a genetic blood test that looked for 5 different chromosomal disorders, so there are tests out there that are even broader than Harmony. The chances of getting a false negative at the combined and another false negative with Harmony are infinitesimal as both tests have very low false negatives anyway.