I also think that this is hereditary. I had a normal labor with my son, painfull contractions 13 hours of labor. Then 2 years later when I had my daughter, I had very low amnio fluid and they wanted to delivery the baby a couple of weeks before my due date. I was not looking forward to being induced, I thought it would be much more painful. But I had painless contracts throught out the whole induced 12 hours of labor. Only had pain during the pushing part. This is also what happened to my Mother when she delivered me. She had 2 normal pain filled labors with my brothers. Then me nothing.