Systic Fibroses screening for grandparents

I am 11 weeks pregnant. My SF screening came back positive. Now we're waiting for the results of the father. I'm caucasion my husband is African-American. Before finding out what the results from the father are, we got a call from our ob-gyn office to have my parents tested also. (They live in Holland). I did not get a clear answer why this is necessary. Exept for that I have a rare mutation on a gene, they want to know were this came from. This is all the information they gave us.
My question is; why go to the extent to have the grandparents of the baby tested also?
As you can understand we are very worried about the health of our baby. Now we are waiting for the results from my parents also, and we don't really understand what those results could mean. We would very much appreciate an answer.
Thank you, Ingrid and Frank.

[National Jewish]

Since you are most concerned about the health of your baby, the two most important test results would be from you and your husband.  The cystic fibrosis (CF) testing of your parents is to learn how you got your rare gene mutation.  Although this gene mutation may not affect your baby