I'm not sure the approach needs to be any different than any other portrait. (I just realized the link goes to a page of thumbnails, the one I'm referring to is in the third row down. all the way to the right.)
I like it too. File my rules in
the bin alongside the Rule of
Thirds and all the other rules
we observe in the breach. :-)
IR can be great for pregnancy - it tends to minimize stretch marks.
What you shoot really depends on what the pregnant woman wants. I like lots of skin, but have done pregnancy shoots where all clothes remained in place. I've shot the "hands making a heart" on the belly because I was asked to. I introduce my own ideas as well, but the client is in charge. Here's some of my pregnancy stuff (there's more in my gallery and tons more in my files here):