Downs Results - do you know how its calculated?

[kmini]

Hello

We've just had our letter re downs results. It has come in at 1 in 158 which is lower risk but close to the the high risk category of 1 in 150.

Just wondering if anyone understands how it was calculated. I know it's some combination of the NT measurements, bloods and age. But what are the components??

With DS my NT measurement was 2.0 and my age was 34. On my notes it says my trisomy 21 background risk is 1 in 330. I didnt keep any notes from my DD for some silly reason. This time around my NT measurements 1.8 and my risk 1 in 158 and my age is 41.

We are considering having further tests but obviously these arent without risk either.

I suppose I'm wondering how much of my risk calculation this time is age. Is it significant element of the probability?

Any help very appreciated. Thank you!

I would say aged plays a bit factor.

I didn’t keep notes from my DC1, but I was 27 and recall
It being very low risk 1/ over 10,000

DC 2 - Age 34 - NT 2.0 - 1/8000
DC3 - Age 39 - NT 2.2 (but done 2w further on) - 1/901

So a big difference

We had opted anyway for the Harmony Test as this is non invasive and much more accurate than the NHS combined testing. My results came back 1/10000. Is this something you might be able to look at ? It’s approx £400.

Although your results only give you a 0.6% ‘chance’

age*
big*

Thank you @walkingmeaway.

The Harmony test is definitely something to consider.

Just curious about your probabilities. My notes from DC1 said:

Background risk: 1:330
Adjusted risk: 1:6205

Do you think your numbers reflect the adjusted or background risk?

Thanks
Kelly

Age is the big differentiator. My DDs are almost ten years apart, first DD had a nuchal measurement of .2mm more yet my chances with her were in the 10000s and with DD2 it's around 1:1500

When I had my son at 42, I was told my combined test results would be "high risk" simply based on my age (regardless of NT measurement or any such hormone level). We got the Harmony test done which came back as low risk.

So yes maternal age seemed to be the big marker.

I'm scratching my head a little why some of these risks are coming back in the 1000s and mine are coming back in the hundreds. Feels like I'm comparing apples and oranges.

I think age makes a huge difference. If you look at charts of DS probability by age it's an exponential curve. The unadjusted risk is about 7 times higher at age 40 than at age 20 (although still only about 1 in 150 at 40 which isn't actually that high and obviously the individual risk can vary enormously). For reference my letter at age 37 was 1 in 273 age related (I was lucky my individual or adjusted risk was less than 1 in 10000 on the NHS test).

The other poster has to be quoting adjusted risk. Even at age 20 the unadjusted risk is about 1 in 2000 which is a higher risk than they quoted for DC2.

If you're worried NIPT could be a good option as it isn't invasive so no risk to baby and is more accurate than the NHS one for Downs if you can afford it? It is still a screening test so won't give a definite answer but is pretty reliable if it says the risk is low, at least for DS. It's a lot less accurate for many of the other things they look at from what I understand.

Its a combination of age, NT measurement and hormones from the blood test - pappa A and HGC i think. No matter the NT and hormone results the higher the age the higher the risk. The fact you are 41 will likely be what has pushed you into the 100s rather than 1000s.

If you have all your measurements/results you can do an online calculator e.g. fetalmedicine.org/research/assess/trisomies

My results quoted are adjusted risks.

According to this table your age alone puts your risk at 1/70 so your adjusted risk is better than this. But like I said it’s still very minimal. And if you’d had issues with your blood HCG being too high or PAPPA being too low they would have discussed this with you. As they can adjust the risk and be signs of other issues.

www.qmul.ac.uk/wolfson/services/antenatal-screening/screening-tests/calculating-the-risk-of-downs-syndrome/

Personally if I was you I would opt for Harmony to ease your mind x

Thank you for all your responses. You are amazingly helpful!!

Just had a very informative call with the Screening Coordinator. Hopefully this may be helpful to someone else

So four things

Age: at 41 my age only risk is 1/86 at 34 it was 1/330
The remaining factors are translated/calculated into MoM values and then are compared to a value of 1 with lower being being better.

Nt: 1.8mm was calculated as a mom of .95. This is good.
PAPP-A: 0.95 again. Also good
HCG: mine is 2.49. So not good but apparently not a bad level necessarily, it could just be something that happens in my pregnancy. Abnormal would be above 10, but the number will still feed into my probabilities in an adverse way. On a side note my hcg with my son was less than 1. So maybe a little bit of a flag.

The Screening Coordinator wasn't sure but she thought i would be unlikely to have a risk level better than 1/500 at my age.

I think we will have the Harmony Test. If I'd known this about the odds when you are older a few weeks ago I would have booked it regardless.

Another week of hiding the pregnancy from my other DCs.

All sounds pretty positive! I think if you’re in a position to have the NIPT then that’s great, as will put your mid at risk.

Also you can find out the sex, if you want to !