Kokoro is a popular one, probably has USP pharma grade progesterone - haven't heard of any natural ones working quite like the pharma grade. Reason I asked for the brand is to identify exactly what you were puttin' on into your body.
Anyway, I don't think iodine/iodide affects/chelates hormones like progesterone, but it probably plays a role in hormone receptor sites. I've compiled a few links for you... check out the responses too.