I rode my indoor trainer with my first child basically up until I delivered. I would spend 40 - 60 minutes on the bike. I backed off during my third trimester though. And was back on the indoor trainer about three weeks after delivery.

With my second child I rode my bike until I was about 5 months along and then switched to the indoor trainer again. I would just make sure to check with your OBGYN and make sure you have their approval in whatever activities you choose to do.