I'm going to chime in with my 2 cents worth. My pregnancy stories are old (my youngest is almost 21), but I think you should proceed cautiously. I exercised vigorously through both pregancies, and I know my HR probably went over 140 at times. But, i was doing aerobics, so the balance issues were not present and i modified the high impact stuff after the 4th month. With the first one, I did classes 6 days a week through my 8th month. Then I walked and swam for the last month. With the second, I was in even better shape. I continued my normal gym stuff until, one day when I was just starting my 8th month, I decided we should go on a family ride. I was not a real cyclist at this point, but I had been riding my 5 speed pretty regularly before the pregancy. Guess what. My husband stopped short in front of me and when i stopped fast, the old fashioned tube shifters jammed into my stomach. It hurt, but i didn;t think anything of it. Five days later i went into premature labor. I ended up in the house for 6 weeks until I was safely at 36 weeks. So, you never know. I think my balance was off quite a bit.