A stillborn fetus in a cat will not stay in the belly forever. It will be slowly expelled through uterine contractions, but it is best for the owner to help expel it so as not to affect the cat's health. If a cat has a stillbirth in its belly, it must be sent to a pet hospital for surgical treatment in time. Otherwise, bacteria will be produced in the cat's body for a long time, causing uterine infection and death of the cat.