this fic sounds EXACTLY like a fic i read on petulant poettess and i think that this is it although hermione does not become pg till later severus is heidden and he gives her a ring but the ring is used more for communication and he changes his appearrance so she does not become scared of him and they end up in a sex ual relationship and hermione has to wear the ring and she becomes betrothed to sev a dragon does emerge when she is in danger
In Annulo by Lady of the masque!!!!
http://www.thepetulantpoetess.com/viewstory.php?sid=1480