Freaking out a little

I honestly don't know if I even have a reason to. My sister has T18,passed away when she was 3 days old, Now that I'm pregnant I constantly worry about my baby having a chromosome disorder. At first I had decided I'm def doing the blood test, and now that it's ordered Idk if I want to! I'm terrified of a positive...but really I don't know if I have a reason to be so worried. Ugh