my 1st was a "big" baby
There are too many factors to answer this question for everyone. But personally speaking, my first child was 8 pounds 6 ounces at 41.5 weeks and I believe it did affect my birth, being hard to push him out. But really the fact that medical staff put me through unnecessary interventions probably had more to do with the problems I had. They gave me the epidural too late and I couldn't feel anything to push. On top of that, nobody tells you about having an episiotomy, as being the worst thing ever. Mine never healed correctly (had scar tissue), and was delicate up to a year after birth. All in all, I am not certain these problems were just because he was big, I think they were more due to being forced to labor on my back and hooked up to ivs, given drugs, and being on cut on.
Maybe not every woman finds it as painful though?