Baby Fever?

The subject that we discussed in class today was one that I have been nervous about for a long time.  We discussed how having a baby can affect marital happiness and satisfaction, usually for the negative.  Sometimes I get "baby fever," and I think about how much fun it would be to start a family.  Soon after I begin, a lot of fear and worries seem to take over.
I worry because I have observed so many families in which the feeling in the home drastically changes when children are born, and not in a good way.  I see visions of screaming babies, nagging wives, and emotionally distant husbands.  I really want to believe that that won't happen to my husband and I, but I am not there yet.