I reall wonde if there is a physcological thing going on for people who don't know they are pregnant. My cousin didnt find out she was pregnant to 5 or 6 months along and she still had her period, didnt get any bigger etc etc. As soon as she "found" out she was pregnant it was like her belly grew overnight, so maybe physcologically for those people who dont know or dont want to admitt they are pregnant they manage to supress some of the symptoms?