The theory is that it would also reach the fetus - and if you are carrying a boy, effect the development of his genitals.
I also came across a medical reference regarding a pregnant woman with elevated testosterone who reduced it with Glucophage to prevent androgenization of a female fetus:
http://jcem.endojournals.org/cgi/content/full/84/5/1510
Have you tried going back to your dr. and trying to find out the cause of your elevated testosterone? Such as if it's insulin, then Gluc. is the answer, if it's adrenal, then another approach, such as dexamethasone treatment might be warranted. I think if you are TTC, you need an excellent endo to help you through this. I'm a big believer in that high testosterone has a CAUSE, and requires an explanation, it doesn't just exist in a vaccuum. You know what I'm saying?
Good luck
