Wishing you all the best with your birth. And if you feel the need to give some kind of explanation maybe just something like "there are a few concerns that we have discussed with our OB and we are doing what is best for baby and for me". Of course different answers are applicable to who is doing the asking, but its your choice and if you think a person is going to debate the issue with you then dont give them your reasons as this will just be an invitation for them to argue them....

But GL with your birth, its the outcome tha is important. Mum and bub, both happy and healthy!