Do you feel comfortable with your doctor AND teacher for the Les Mills classes?
Talk to both of them and see what they think.
I've heard both sides of things - Don't do any strength training, aerobics, or any type of exercises to Do whatever you want, just know your limits.
It's SO difficult to get a clear cut answer. I think if you did Body Combat (Never had that class), or BodyPump, you can explain to the teacher that you're pregnant, so you can modify the workouts. If they requires you to jump up and down, jumping jacks, or anything that makes you out of breath - modify it by just pumping your arms instead vs jumping up and down (I've heard that's not good, no matter what week you're in).
BodyPump - use lower weights instead. I really would like to do that class, but I'm going to wait until I get the go ahead from my doctor. I will explain to my teacher beforehand that I'm not trying to be a wimp or avoiding the workouts. I want to have stronger arms and legs, so it'll help.
Same idea goes for everything else...just kick it down a notch. If you're tired, step out, and back off.
I've had a friend that did a Squat lift with over 150 pounds on her shoulder when she was 6-7 months pregnant. She stopped because the belly got in the way. LOL!
Again - talk to your doctor and the instructors (I'm sure they've had many pregnant women taking their classes). If you're high risk, or have history with issues with your uterus or anything of the sort, I would just skip out on all of this.