More confusion over blood test results nuchal/risk etc

[mosschops30]

I ahd a nuchal last week and the measurements were good 2.3mm, which took my risk from 1:353 (background risk) to 1:613.

However when the consultant phoned me with the blood results the risk had been adjusted to 1:301 (their cut off for offering further testing is 1:300 so we are borederline). I spent an upsetting weekend crying and then spoke to ARC who were wonderful and have suggested I speak to the NHS screening MW and my private consultant.

Have now just received paperwork and although the above figures are the same, there is another figure which is a biochemistry risk, this is 1:174. Can anyone explain what this is?
Is this the risk from the bllod test? Is it only made up to 1:301 because of good nuchal?

Any advice would be good thanks

The biochemistry is usually the downs screen or triple test. Your risk might have gone up because of your age???

yes it is for downs screening, which is what the nuchal was for.
I just wondered what the relevance of it was

I think it means that on average 1 out of every 174 women with your biochemistry result would have a baby with a problem. But if you were to line up all the pg women in that hypothetical group of 174 in a line according to their nuchal fold measurements, you'd find that the risk would be much lower than 1 in 174 at one end, and much higher than 1 in 174 at the other. You're standing at the lower risk end of that line, so your risk has ended up lower.

In other words (at least this is how I worked it out when having nuchal tests) loads of people have had exactly your biochemistry results, and on average 173 out of every 174 of them (99.43%) had babies who were fine. And your nuchal-fold result tells you you're more likely to be in the 173 than to be the 1, because when they take that into account your risk goes down to 1 in 301 (99.67% likely to be fine).

Don't know if that helps at all.