stressing !!!!

Carol
No disrespect and I'm not judging in anyway but...  
I'm 38 and about 6 weeks pregnant with my 6th child .... (my youngest is 9 ) is it normal to be terrified of Down syndrome or any other serious birth defects?? I've never been this terrified before and it's starting to be all I think about. I will obviously love my baby no matter what but the stress of this is taking a toll on me being happy