Re: 3rd trimester?
I think its 27 weeks or thereabouts, LOL. I didn't even discuss it with my Dr. I asked him what he wanted me to do (since I wrote out a birthplan) and he said just take it to the hospital when I go in. That's just because the possibility of him being on-call when I went into labor was pretty slim. It's the nurses who help you follow your birth plan in our hospital, all the Dr. needed to know was about the actual DELIVERY part (episiotomy, forceps, etc.).
How many weeks are you? Next time you go in I would just say "I want to discuss my birthplan now, since I tend to have my children a little early". They'll generally listen, if not just make sure you write it out and throw it at everyone you can find when you're in labor, LOL