Oooh you're lucky have my Body Pump manual out by the computer

* See your Doc first
* Lying on inclined platform for the Chest and Tricep tracks
* Perform exercises seated rather than lying position eg Tricep Extensions and Tricep Press (to be honest not sure how you would do a Tri Press from seated lol)
*Abdominal options: Lower ab exercises using the legs as the resistance eg pelvic tilts. Also single and double heel drops.
*Reducing weight and in some cases working with the bar only.

Listen to your body, drink lots of water, dno't overheat and make sure you are careful when stretching that you don't over stretch

I did Pump till 36 weeks...Lees you about the same? Clean and Press is hard around a big belly though lol

ETA - make sure you tell your instructor...