NTScan+bloodtest odds from 1/75 to 1/1423?

[xkat]

Hello all,

Been reading through the threads here and it is amazing how much you all share, and thank you for that as I would not have known about the more detailed ultrasound scan that can be done when determining 'risk' for chromosonal disorders.

So, the long preamble to my question:

I had my nuchal measurement and bloodtest done by the NHS Tuesday, and the call today telling me that I had a 1/75 risk for Down Syndrome. My nuchal scan was fine, a little on the high side, 2.3mm, and PAPP-A was good, low, but my beta hCG was triple what it should be! I knew it as when I first took the pregnancy test, the line immediately appeared and very very dark. So double the normal amount of beta hCP can indicate chromosonal abnormalities (also I am 40) and I am triple. They said I could go to the Harris Birthright Centre @ King's College for CVS.

After the call this afternoon, I read on here about the Fetal Medicine Centre and called them immediately, since my gestational date was wrong by a week and half (I wasn't 12 weeks at the NHS screening, I was actually 13+4) and they said I should come down right then for a screening or it might be too late to accurately measure.

So I went down, the doc was wonderful, took a long time scanning and measuring various aspects of the baby and me, including baby heart, my cervix etc, though for the test, it says only nasal bone, tricuspid flow, and ductus venosus were the added markers. So, my new 'risk' is 1/1423.

My question is can this really be accurate? I expected maybe a difference in the tens, not in the hundreds! I don't see how it can be so different as beta hCG reading was exactly the same, PAPP-A same and the nuchal scan actually showed even more thickness! Does the nasal bone etc. really have that much weight?

Any insight is welcomed! And as I've already mentioned, thanks for all the helpful wrods posted in these threads.

Love, k

[ragged]

I may be wrong, but the precision in your actual due date may be the other main reason for the dramatic change in risk.
Keeping in mind it's only a risk stat, nothing is definite.
The FMC originally developed all these tests, I would trust their numbers more than anyone else's results.