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triple tests - please help me understand the stats...

5 replies

StripyMouse · 26/06/2003 23:14

Sorry, this is going to be a bit rambly and confused as i am really struggling to explain my confusion! Thanks for putting up with me and hoyou can help sort me out!!

I have just had my triple AFP blood tests back and am fortunate enough to receive what seems like fairly good news - 1/525 for my age of 31. I know I should be happy and relaxed about this and I guess I really but there is a couple of niggles in the back of my mind - for my first pregnancy (only 2 yrs ago) I had odds of 1/3000 and therefore the seemingly good odds of 1/525 suddenly look not quite as good as they this a reasonable response or is it totally unreasonable/illogical to compare the two?
Also the way my mw told me left me wondering just a little bit - she said "well, the results are fairly reasonable for a woman of your age" - what does she mean by "fairly reasonable" - why isn?t is "really great" ? wish I had picked her up on it at the time.
I am not so concerned about my odds as logically they are great, my problem lies more in my ability to get my head round the stats - I understand the basic facts about stats and that the tests aren?t definitive, picking up only approx. 60% of Downs cases etc. and have done a fair bit of research but what I don?t understand is how to put this into a real working context - ie. hypothetically, 1/800 is in the negative/low catagory - but for a healthy 22yr old this might be classed as normal odds whereas for a 45 yr old this might be seen as exceptionally good results back from a triple test if you understand me. Therefore, where/how can you put the results into a more manageable format? Is there somewhere that actually states what is normal for different age brackets or is this just impossible/too misleading to calculate? I am not looking for reassurance for my own results as I understand that I am low risk and should be grateful that I am not in the awful situation that many parents find themselves in - and i am grateful, just confused about how to view it overall. Phew - if any of that made sense and you can see where i am coming from - please put me out of my misery! Thanks

OP posts:
pie · 27/06/2003 00:19

From what I've read Stripey there is a fair amount of controversy over the Triple test, not only for missing out potential problems but also for a high number of false positives. So even if you had come back as high risk , that could have been misleading.

I found this when I was waiting to have my amnio. It would look like you are not far off what I guess medics would expect.

I guess you know that the thing to remember that these are only odds. So, yes by this chart the 20 year old has a 1 in 1529 chance of delivering a baby with DS, but even with the low risk she could still be that one.

Have you have a nuchal scan?

Sorry for adding my rambling to yours!!!

WideWebWitch · 27/06/2003 14:57

Could you try calling the Fetal Medicine Centre in Harley St? I would imagine they would be able to help you, or someone at King's would.

StripyMouse · 27/06/2003 20:01

Thanks for your posts, Pie and www. Your link , Pie, was exactly the info I was after - just a straight forward blunt average based on age to use as some sort of context to these numbers. I realise that the stats are pretty unreliable and that using age is rather arbitrary but it has satisfied my curiosity completely - using that chart for my age I work out as fairly close to the average risk which is good enough for me and has explained clearly how the figure drops dramatically dependant on age - fascinating, God knows how they work it all out. Thanks for the suggestion of the Harley St contact www - luckily I needn?t bother them now but it would have been my next port of call if I were still confused. I would have loved to have a nuchal scan as a better alternative to the triple but was unavailable on the NHS in my area and was told about it so late that it became virtually irrelevant - I had only 2/3 days to get one booked... It was just as well as we could not have justified the expense at the moment.

It must be hormonal - I can?t believe that this issue has been such a big deal for me and that I have become so easily obsessed by the subject of stats. If we are fortunate ever to have more children I am NEVER taking any non specific, potentially misleading diagnostic tests again - and that is a promise.

OP posts:
SofiaAmes · 27/06/2003 22:37

StripyMouse, I went through the same as you with my second pregnancy. I was 39 and got a reasonable result on my nuchal scan. For some reason, I started getting all agitated and worried about it (I had been totally fine with the reasonable result from the blood tests from my 1st pregnancy). I finally decided to get an amnio just to let me have a calm pregnancy. I felt that both me and my baby would be better off if I wasn't worried all the way through the pregnancy.

StripyMouse · 27/06/2003 22:58

Nice to know I am not the only one SofiaAmes, thanks. The one strange thing in all of this is that before my pregnancy I believed that if I found out I was carryng a baby with Downs we would at least consider our options very carefully. However, I am even more anxious about the results than my first pregnancy but at the same time absolutely 100% firm in the knowledge that there is no doubt we would keep this child regardless, DH has also come round to feeling strongly about this as well. So, I still have no idea why I have been so concerned! Maybe it is just the jarring of the facts - on one hand being given very precise mathematical figures and yet at the same time being told they are virtually meaningless in that they only pick up 60% and is only an estimate...just doesn?t compute in my small, tired and hormonally charged brain!

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