First off: Congratulations. Kids are great. If this is your first, My advice is go out to eat with your partner now because after the baby comes, you never leave the house without your hands full: diaper bags, clothing, baby, toys etc.

As to your question: Similar experience to ahpook. My wife would cycle with me while she was pregnant up until she started having balance issues. That was around 7 months. She started swelling up like a balloon and our little bundle of joy caused difficulty mounting the bike safely, as well as leg motion once she was on. After she almost fell down just trying to mount the bike, I made her stop. Her doctor didn't have a problem with it so long as she kept her HR in zone 1 with occasional forays into zone 2. This wasn't a problem for her since she was riding alongside me while I was training for a half marathon. Her experience was recreational riding. 5 miles was a long way for her to ride at first, but I had difficulty giving her sympathy due to her sore legs from riding a bike next to me while I ran 10 miles