Re: 3rd trimester?
I'd recommend going over it no later than 34 weeks or so, just because your dr. has a lot on his/her mind and might forget the specifics if it is very much in advance of the birth. That's probably why they usually do it at 36 weeks. I had some requests that were against "hospital policy" but because I had discussed it in advance with my dr. she was able to be my advocate and override them, so my birth went much better.
Carrie (28), wife to Mark (31), mama to identical twin cuties Ethan and Ryan (27 mo.)