Impact of negativity, anger, stress on unborn baby?

A few women on this board made me think of how their unborn babies might be impacted by all the negativity and stress. 
Does anyone know of any good research on how stress impacts the fetus? I know we have a few doctors and other medical professionals, I am particularly interested in your opinions.  
Also before you get all snippity, I posted anonymously because I didn't want anyone to think I was specifically talking about them.