This is definitely not Pets compatible.. sorry.. and I even ran hack detection utility to make sure it wasn't something else.  When my sim changes clothes other than maternity wear, her belly disappears. After showering or bathing, she automatically changes in everyday and there is no belly.  Also, when she goes swimming or changes into pjs for the night, she just wears her normal pjs or swim suit and her belly goes away as well.. The hack isn’t crashing anything or messing up game data that I can tell, but it’s not hardly usable in its current condition.