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Antenatal tests

Thinking ahead, need to know what to ask for.

5 replies

nosleepwithworry · 08/07/2012 10:53

I just want to educate myself, dont really want to google as i dont know what it will throw up.

So i wondered if you would mind talking to me.

What abnormality tests are there out there and when should they be carried out?
Is CVS more informative and accurate than amnio?
What about risks?
Nuchal fold measurements, this is just for Downs right? Plus it is completely non invasive?
Whereas CVS is more detailed but very invasive?
This is the extent of my knowledge, patchy and not in depth, so what else do i need to know?
Thanks very much x

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ghislaine · 08/07/2012 17:01

The most common chromosomal abnormalities are Down's, Edwards and Patau's syndromes (trisomy, 21, 18, and 13 respectively). Also common (relatively speaking) is Turner's syndrome (this affects girls only). Indicators or soft markers for these can often be seen at the 12 week scan. I think there is a lot of variation as to what tests are offered across the country. Some trusts look for lots of soft markers and combine it with bloods, some look at the nuchal fold only.

There are also structural abnormalities eg anencephaly (brain related) or spina bifida or cardiac problems or other organ problems. These can be seen sometimes at the 12 week scan, but some aren't detectable until the 20 week scan.

CVS and amnio are basically the same procedure done at different stages of pregnancy. A sample of the baby's chromosomes are extracted for analysis. There's an initial result, which looks for the chromosomal problems I just mentioned, and then you can also get the full chromosomal karyotype which shows up everything.

The quoted risk for miscarriage you'll get for CVS is 2% and amnio 1%. In reality, the risk is much lower - these stats are from the 70s when these procedures were done blind. Now they use ultrasound to guide in the needle. And individual consultants who've done thousands of these probably have even lower risks.

The nuchal fold measurement is an indicator for Down's syndrome (I'm not sure about other chromosomal problems) but it can also indicate heart problems.

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Nigglenaggle · 08/07/2012 17:02

Ok the bits I know are: Nuchal fold measurements are completely non-invasive, its just something they look at on your 12week scan. Its interpreted in conjunction with a blood test. It tells you whether you have a risk of having a Downs baby, but isnt diagnostic, it doesnt tell you for sure. I dont see any reason not to have it done, found it very reasurring my Downs risk came back as 1 in 10000. If the risk is higher you can choose to have further tests done or not depending on your take on these things. Its good to remember that even a risk of 1 in 100 means there is a 99% chance your baby will be normal.
CVS and amnio are diagnostic but more invasive, with approximately a 1-2% chance of miscarriage. You can ask what the risk is for your particular hospital before you decide if you want to go ahead. Its only done if your screening test shows you are at risk.

I highly highly recommend the book 'Expecting' by Anna McGrail and Daphne Metland. Its evidence based, easy to follow and has good common sense advice

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LittlePoot · 08/07/2012 19:56

All of the chromosomal problems can cause high nuchal fold, not just downs. But downs is the most common so that's the one talked about most. Actually, a really high nuchal is usually a different problem. But more often than not, everything will be absolutely fine so please don't let all this worry you! x

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nosleepwithworry · 09/07/2012 13:35

Thanks for that.
I think i would rather know definitively rather than be given possibility iyswim, but i am hyper anxious about the invasive investigations and the chances of miscarriage.
I know that they are USS guided, but wonder why they do not publish current rates of miscarriage based on the "belt and braces" approach of uss guidance.

I know what course of action i would take if there were indeed abnormalities, so it would be with good reason that i would go ahead with the testing.

I am still unsure about the timings of the tests, it appears that it depends on where you live and what your local Trusts policy is.

Seeing the MW next week, will ask.
Thanks again.

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Nigglenaggle · 09/07/2012 21:11

Also remember that you get a second chance to pick things up at the 20 week scan, so whatever your risk you can wait until then rather than have amnio if you arent sure

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