As a perspective adoptive parent, we are very nervous about our meeting with our birth mother? Are there things we should or shouldn't say?

You should focus on being yourselves, letting the birth parents get to know you and establishing a comfort level. You want the birth parents to have concern and empathy for your situation, and for you to understand theirs. You should not be interrogative, ask for personal or confidential information or question medical history. If you have a question in this regard, let your adoption professional handle it.