I saw the chiro 2x a week from about 20w until the end of my pregnancy. It helped a little, but my labor was pretty horrible. I had horrible back labor. I literally felt nothing in my belly, no cramping, nothing, but my back and hips felt like they were breaking for nearly 30 hours. I got an epi after about 15 hours, starting pushing 4 hours later for roughly 3 hours, and delivered her.
That being said, I have no idea if it had anything to do with sciatica.