"Oxytocin is a hormone that has effects on brain function. Although it is best known for its role in facilitating labor, delivery, and breast-feeding, it is also important in promoting trust, love, and social recognition." (Quote from this article)It is an absolutely enormous part of labor, and being nick-named the love hormone, it is also produced with human touch, intimacy, empathy, and breastfeeding to name a few. Naturally occurring oxytocin enhances the immediate mother-infant bond, and as the icing on the cake ... it dulls pain!
Therefore, if you are able to start labor spontaneously (without medical induction), you will have a natural pain killer going and you will be greatly helped. If you are induced, you will be much more likely to require pain medication as you will not have the oxytocin flowing yet and the contractions will likely be extremely intense.
So, if you are contemplating a natural birth, here is one more neat little fact for you to gain a little more confidence in your body's abilities.