Down syndrome test.

Theresa
I had my first blood test two weeks ago at my 16 week appointment. I got a call today that my baby might have down syndrome. So now they want me to do other tests. I'm so worried,this is my first pregnancy and I want a healthy baby. Believe me I will love this baby no matter what. 
But has anyone had to take other tests to look further into it? Please share with me and make me feel better.