Can someone advise low risk on NT and trisomy?

[SukieQ]

I had to wait for the NT scan results for over two hours and then had to get back to work so they sent them in the post instead of explaining them. They called and said it's low risk, but can you help with what the actual results are and what the norm is for low risk? I have no idea what to compare to, as I'm first timer. I think it's all normal but wanted to know the 'ballpark' figures considered low risk.

Was taken at 11 w 6 d. All looked OK on the scan.

NT: 1.71 mm

Trisomy 21:
Background risk 1:990
Adjusted risk 1:33008

Trisomy 13/18
Background risk: 1:8203
Adjusted risk: 1:273422

Nasal bone and fetal blood flow were OK.

There's a paragraph at the end of the letter they sent which is confusing me where it says "the risk was low (less than 1 in 150)" so I'm confused as to whether 1:150 is the low risk cut off, or if is my risk that adjusts to 1:150 somehow?

Thanks for guidance.

1:150 is a threshold they use, not your numbers at all.

That's all good news, relax! xx

I don't know if this is helpful in understanding the results.

Your risks are extremely low. The background risks are both low because of your age and then when they adjusted the risks to take into account your test results it made the risks even lower (so very good news) because all was ok on the scan.

The adjusted risk is your personal risk after the scan.
eg. 1:33008 means that if 33008 people with the same background information (ie age) and scan results all had a baby - only one of them would be expected to have down's syndrome - so you can be reassured

thanks for that - really appreciate the advice and making sense of the stats.