So what’s the connection? Cats may ingest toxoplasma, a nasty microscopic parasite often found in undercooked meat—and in mice or birds they happen to catch.
It usually does not harm cats, but since it is passed through the feces, it is possible for a human cleaning a litter box to take in the toxoplasma. If that human happens to be a pregnant woman, the toxoplasma can cause severe damage to the unborn child. So, as a general rule, pregnant women should avoid litter boxes.