Congrats on the baby!
I think the last time I rode was when I was 4 months along with my pregnancy. I got away with it because I wasn't really showing. I went from riding 8 horses a day as a trainer to riding nothing, so I was itching pretty badly. I went horse shopping and rode some prospects before finally settling on a little black unbroken mare.
This kept me occupied through the winter, since she was untouched and basically just needed fed and cuddled and ground mannered. I fed all through winter (which was harder and harder seeing the grain was kept in a huge freezer and after a while I couldn't bend down into it!). I also did a lot of problem solving when I had to move grain and hay since I wasn't able to do it the way I was used to (you know, carrying it!)
When I was around 8 months I started her on the lunge and just did a lot of ground work with her, getting her ready for a rider.
Within a week after I delivered, I hopped on her for the first time.
I got through it by setting a goal through my pregnancy and working on it. I also wrote a blog during this time to show her progress and was able to log the things I did.
You have to be very careful though and use common sense when dealing with a large animal while pregnant, however. If she hadn't had such a sound mind, I would have never been around her. Accidents do happen though. She gave me a black eye during feeding time once because I couldn't move fast enough and we knocked heads. She got a lesson in patience after that and I got a lesson in caution.
Maybe you could set some goals to do while you're pregnant. One that you can only achieve after baby is born, and work towards your goal at a slow, steady pace. That's what got me through it :)