Subject: Two placentas, one baby.

A few days ago my mother and I were watching a medical mysteries television 
show about human chimeras. My mom then said that it might be possible that I 
could be one because when I was born, there were two placentas. I don't really 
know if this is the case, but I searched the internet for information about 
situations where there were two placentas and one baby. I didn't find anything 
(except a article listed in google that had the same title as my question, but 
had a bad link). Now, I just want to know what could of happened. My mom 
remembers that the doctors said this was really odd. 
I also searched for information about chimera births, and nothing really 
expanded on what happens to the placenta in these situations. If two twins 
fuse, will there still be two placentas or just one? 
Any information about this kind of situation would be appreciated.
Thanks for your time!

Re: Two placentas, one baby.