I'm not too sure which causes the hike in the risk.
Here's what I see on the report
Nasal bone: present
Nuchal translucency: 1.15
Age risk: 1:742
Biochemical t21 risk: 1:59
Combined trisomy 21 risk: 1:162
Trisomy 13/18 + NT : <1:10000
I have also seen reviews of the high false positive rate...