Well, not to be a negative or anything, but doesn't sound to me like you are really ready to have a child. If you have to refer to your niece or nephew as the thing, or are already worried about jealousy from being left at home, I wouldn't suggest having a baby.
Having a child is a sacrafice on the part of mother and father. You will not be able to do the things that you want to do all the time.
When we had our son, we got a trailor and pulled him around until he got to heavy. Once he was too heavy, we kind of put the bikes away. He wasn't old enough to keep up and it would have been dangerous. Then between work both of us working and life in general we just didn't get to ride. We have since taken it back up again. He can go now if he wants but he is also old enough to stay home for an hour or two while we go.
There are many ways to keep in shape while pregnant and after besides bike riding that you can do and still have a baby. You can also, see if someone you can trust is around if they will watch the baby while you bike. Or hubby and you can take turns. There are always ways to work things out if you want it bad enough.
I just hate to see you have a baby if you are already feeling like a child would tie you down and make you resentful.