Quad results

Naty

I initially did the NIPT at 12 weeks i think and came back for low risk for Down syndrome . This past weekend for my 17 month mark I did the quad and now it’s saying high risk for Down syndrome . How can this be ? I heard the NIPT is more accurate. And many ppl asked if the Nipt was normal they shouldn’t have done the quad but I guess my doctor still ran it anyway. Opinions? Comments ?