Have you ever seen prescription medication having a label like "Pregnancy Category C?" I actually just noticed that recently.
I was wondering what that was all about, and I found this PDF that explains it all.
Basically, the FDA has these categories (A, B, C, D and X), which let you know the risk based on past studies (if there are any) and potential benefits.
I also learned a new word: teratogen. According to Wiktionary, it's "Any agent or substance which can cause malformation of an embryo or birth defects." The PDF above has a list those, as well.
Of course, different medical professionals will have differing opinions on medication during pregnancy, but this is good information to check out and possibly a place to start the discussion.
Edited to add: I fixed the link on the PDF - it should go to http://depts.washington.edu/druginfo/Formulary/Pregnancy.pdf
Photo by abardwell.