I had some back labor with my first, and not with any of the others. I didn't even know it was labor because it just felt like a dull throb in my lower back. I didn't realize it was worse in waves. Then, the back pain subsided and I started getting cramping feelings in my abdomen like menstrual cramps. These felt nothing like the BH contractions I had been having. Some of those did take my breath away, but were rarely, if ever, painful, and I definitely felt my whole belly or a good part of it hardening very much. When this real labor started, I didn't feel my belly hardening at all for a long time, so I didn't know I was in labor. All I knew was that the cramps felt better when I was in the tub. My husband and I started joking about this possibly being labor and wouldn't it be funny and just for fun, lets time them (my menstrual cramps always came in waves, so this didn't seem unusual to me)... oh, look, they're three minutes apart, how interesting.... etc. I only got out of the bath tub because I had my weekly scheduled appointment with the doctor. Getting out of the bath did make the pain somewhat more intense and by the time we got to the doctor's I was also feeling some tummy tightening, although nothing like as hard as the BH had been. We had gotten to the point where we thought it might actually be labor, which was confirmed by the doctor after we got there.
For the last three babies I've had, I never had much back pain, or else if I did it was negligible. Mostly it just starts out with some lighter abdominal cramping that gets more intense. I have noticed my tummy hardening a lot more with the last three than I did with the first... but mostly they were just like really really bad menstrual cramps accompanied by a BH of varying degrees... until the end. Transition to birth generally lasts between 10 and twenty minutes for me so at the end I really feel like a train is battering it's way out with all the pain and pressure... but since it doesn't last very long for me I can handle it. If more of my labor was like that, as high a threshold for pain as I have, I might give in to some kind of relief!