|Pregnant women should not clean litter boxes because cats and kittens can carry an intestinal parasite called Toxoplasma. This parasite does not generally cause significant disease in felines, but it can cause birth defects in unborn human children. The organism is found in the stool of cats. Although the disease in cats is rare, it is best for pregnant women to avoid cleaning litter boxes (and gardening in areas where cats may defecate).
Toxoplasma can also be found in the muscle of many animals, so eating undercooked meat is the most common source of infection in people.