I agree with the the girls that have posted.

I have a PT (Personal Trainer) and I see him twice a week, I am still doing weights, a lot of core work (keep those ab muscles tight!!), but a lot of my exercises have been modified and have significantly cut back the amount of weight, I was lifting the equivalent of my own body weight plus a little more. I borrowed a HR monitor from SIL for a couple of weeks so that we could get a good idea what my heart rate was doing, what the recovery times were etc.

The other major change has been minimising work on my back (especially after about 16 weeks), it blocks off the major artery, cutting blood supply due to the weight of the uterus.

I have stopped treadmill work due to pelvic instability and it just get too sore doing it, and I did have about a week or two off around the 10 week mark due to some spotting, but been back at the gym since.

I intend to be exercising up to the birth, I have also started going to yoga and will probably go to aquarobics in the future as well.

Good luck hope you are UTD really soon, and keep up the work outs