This is absolutely the wrong time period! The most trying time for a woman is right after child birth. You are talking about someone with homones going insane, over tired, and most are feeling unhappy and insecure it their post pregnancy body! Now add in the conversation of what your thinking and the most likely thing to come to mind is probably "I am not good enough anymore"
That being said....Quath is right about mentioning the show or an article and saying you found it intriguing and ask her opinion. The key is conversation, honest staight forward talk...and lots of it. Most people I have met in any kind of alternate lifestyle started out with " what if?" or a fantasy type conversation. You will both need to ask and answer questions on boundaries and jealousy etc. Then you talk about how and who to approach and go on from there.
Who knows, your wife may surprise you and be thinking the same way!
I wish you luck....and congrats on the new baby!