Although I would prefer to run, I was put on pelvic rest for my first trimester. By the time I was cleared to exercise, running felt a little "off" for me, so I transitioned to using an elliptical when I was at the gym and walking outside when I was home. I wore my fitbit daily and made an effort to get 10,000 or more steps everyday. There were days I was exhausted, but the fresh air and endorphins I got from the exercise helped me keep going. I recruited my husband to walk with me in the evenings and it was also a nice time for us to chat and catch up on each others days.
By making an effort to keep moving almost as much as I did pre-pregnancy, I experienced minimal swelling and less sleep issues than anticipated, which I'm sure helped keep my metabolism functioning at a high level.