I had my first child unexpectedly at 30 weeks and knew I was at high risk of it happening again with my second. The way it works is you continue to see your regular obgyn and then you also see the high risk specialist- which means lots of dr appts but it's well worth it! With my second child I was put on bedrest at 20 weeks among other things, but in the end she was delivered at full term, which was more than we were expecting. (We were told we'd be lucky to get past week 32!)
I also used Atlanta Perinatal Consultants and they were fabulous. They do have offices besides the one at Northside Hospital. I used Dr. Matsumoto and couldn't have been happier. Good luck!