I have not had surgery, but I did have a herniated disc before I ever got pregnant the first time. I actually found that my sciatica went away during most of my pregnancy because everything was so loose.
Towards the end of pregnancy, I'll usually get a little bit of stuff going on, but most of it is more related to my pelvis, and a chiropractor keeps me walking around relatively pain-free.
The biggest thing is to not do stupid things. Like don't try to pick up something heavy that you shouldn't, or don't bend over the wrong way, etc. Just remember your basic back care stuff.
Have you been doing back/ab strengthening exercises before getting pregnant? You can continue them during pregnancy. This pregnancy, my back has held up really well because I'd strengthened my abs before I got pregnant, and I continued with abs exercises through most of the 2nd trimester (eventually slacked off).
My back has never bothered me during labor, btw.