If you contract the flu or another virus while pregnant, what symptoms will the unborn baby likely get?

Which virus?: Generally, since the fetus does not yet have its own immune system it depends upon mom. Some viruses, usually during the first trimester, are injurious to the fetus, but most are handled by mom without negative effects to baby. The problem in answering your question is that there are dozens if not hundreds of different viruses you might get.