It's pretty uncommon, but if your beloved pet has one, more than likely you wouldn' even know. If she has a mescarriage, she will eat the kittens, which is normal.
Cat's don't cause a miscarriage, but their cat litter box will cause a very poisious, that will indeed kill an unborn bab; which is a fetus until birth. Don't let pregrant women clean out the cat litter box.