So my husband told me that he had a dream that he was holding a baby but it had something wrong with it. He wasn't sure what was wrong but it made him really upset. We have 3 perfect children and we just started trying for our 4th. He is now feeling nervous. Is this something we should be concerned about?

Well, it sounds like he is worried about something going wrong, not necessarily with your fourth child, but with anything in life. Perhaps, unconsciously, he feels like something is missing in his life.