So is it the relaxin that makes the hips wider, or the actual baby pushing through that makes them wider?

I asked a question a few days ago about the widening of hips during pregnancy/birth. One very knowledgeable person replied that during pregnancy the hormone relaxin is released to loosen the joints and that the hips get wider to let the baby through. What I'm still confused about is if she meant that the noticeable change in hip wideness is the result of the hormone or of the actual baby forcing its way through and pushing the pelvis apart?