Induce at 39 weeks?

LJ • Baby girl born Feb 19, 2015 and second girl born Jan 20, 2017. Baby #3 due in October!
As of my last appointment just short of 37 weeks she was at the 12th growth percentile. My doctor just says that she will be a small baby and that she will be ready to induce at 39 weeks. Is this normal?  I'd really like to have her natural as I was induced with my first.