Found a site with really great (read CLEAR) advice for working out with a Cross Fit/ P90X type workout. Or really ANY workout, since the ones I mentioned incorporate cardio, interval, weights, flex. etc.
Here’s what it says about the first 4 months:
In the first trimester, there are only a few things to be careful of. For most women, it is ok to lie on the back until the 12-16 week mark, so you can still do sit ups. If you were already doing CrossFit before you became pregnant, you should still be able to do most of the exercises. However, I would recommend dropping weights on Olympic lifts and things like kettlebell swings. 65-75% of your normal weights seem to work for most women. Your blood volume increases when you become pregnant, so trying to keep your heart rate at 140 bpm when exercising doesn’t allow you to do much. Rather than focusing on heart rate, pay attention to your breathing. You should still be able to talk while you’re working out. This is a time for maintaining your fitness, not intensity. Don’t work out until the point of exhaustion and don’t get over-heated. You don’t want your core temperature to get too high. Make sure you rest between rounds or exercises, drink water before, during and after your workout, and as always, check with your doctor before beginning any type of exercise program.