Make use of the low intensity options
Maintain good hydration
Don't overheat the body
Abs - if lying on the back becomes uncomfortable, hands and knees and extend the hand and/or leg
I teach bodycombat in the netherlands and right now we have a girl in class whom is now 20 weeks pregnant. She takes the options, don't do the jumping knees, but further on she wil go with the flow and still haves a lot of fun. So I think when you feel ok, take it easy and just try it. If your are not ok anymore then stop immedeatly.
Lot's of combat fun
I taught Combat right through till I was 26 weeks pregnant and just took the lower options eg. no high knee running or jump knees, marching instead of scissors etc.
You will find your body will tell you what you can and can't do. Good luck!
We had an instructor here who did Combat until just a few days before she gave birth....and she didn't give up on jumps much until the end either! I found it difficult attending her classes, because I was constantly worried about her. I think I would have felt better if she had at least used a heart monitor.
I'm currently 26 weeks and am a Combat, Step and RPM instructor. As of today I have given up my Step class to a new instructor and can't teach Combat because of scheduling conflicts with my RPM classes. This is my fourth pregnancy and the last one I taught Combat until around this time, again, I stopped due to a move, not because of my "state". I videotaped for RPM during my third trimester and was fine.
I currently use a heart rate monitor for RPM and am able to keep my heart rate down by removing some tension and decreasing my aggression. I found Combat to be similar in that I could keep my heart rate down by avoiding the jump kicks and using my verbal cues more than visual cues. Step has been different for me as the group I instruct has difficulty following without a high energy instructor. When I ask them to continue at a higher level so I can bring my own heart rate down they follow me even though I explained the situation before class, I don't feel I am doing them any justice. Having a different instructor seemed more fair to them and I will continue coming to the class and showing lower options to those that wish to follow.
The bottom line is to make sure your medical professional is okay with you continuing exercise at a higher level...there are reasons to decrease or even stop if you have complications with your pregnancy. Listen to your body, don't ignore any pain or cramping. KEEP HYDRATED, wear a hear rate monitor because it's hard to judge how hard you're working when you're feeling fine and normally work much harder.
Remember, it's just a short time if you do need to take it down a notch...people understand and will still be very inspired by you because of your activity level regardless of your intensity level. I think you should model what you would like your participants to be doing in a similar situation and after you have the babe...and get the green light you can kick it up to a level never seen before!! (smile) Good Luck!!!