Okie dokie.... well I called Nature's Bounty, the company that makes the cream I have been using, and talked with a dietician there who said that the
progesterone in their cream has been synthesized so that our bodies can break it down. It is derived from yams but she explained how in its raw form that the yam progesterone can't be broken down by our bodies, so that's why they synthesize it for us... It made sense when she explained it.
On a side note, Premarin, made from the urine of pregnant mares, is an estrogen replacement therapy, and has nothing to do with progesterone or progestin.