To get the best (?) ending you have to consume three of the umbilical cords before fighting the last guy, to fight the real form. One is from the Abandoned Workshop, one is from the Wet Nurse, one is from Iosefka, and the last possible one is from killing Arianne's baby once you have sent her to Odeon Chapel.
Well, Iosefka never dropped one for me when I killed her and I don't have Odeon Chapel to send the whore to. So I can't get 3 at this point.
After reading a little more it seems like you have to kill Iosefka after Rom so that she is pregnant, so yeah looks like no true ending for me.