why is it bad to clean or change the cat box while pregnate?

The reason a pregnant woman should never go anywhere near a cat box (or any other place that an animal might deficate) is because of a protazoan parasite called toxoplasma gondii. This parasite can be found in many animals (including humans) but cats seem to be the primary host of choice. Any animal can contract the parasite by eating the uncooked flesh of another animal who is infected or by fecal contamination of an animal who is infected. Normally, getting toxoplasmosis (the condition the parasite causes) isn't a big deal. You may feel some flu-like symptoms but your body does it's job (usually) fights off the infection and you continue on your way probably not even realizing it was toxoplasmosis. But a fetus can sustain terrible malformations from contracting the sickness through the placenta because it's immune system is not yet fully functioning so it cannot fight off the infection.

The chances of contracting toxoplasmosis from the litter box is not very high, especially if your cats are indoor cats and don't get outside to kill and eat small rodents. You have a much greater chance of contracting toxoplasmosis from raw or undercooked meat. So the rules to avoid toxoplasmosis are as follows:

1) Fully cook all meat that you intend to eat and disinfect all areas that raw meat has touched. Wash your hands after handling raw meat.

2) If you cannot get anyone else to clean the litter box then clean it every day. It takes over 24 hours for the eggs in the cat feces to become active and contagious. Where gloves and wash your hands after handling any feces.

3) Avoid gardening and children's sandboxes as these are common places that cats will defecate. If you are going to come into contact with either of these then wear gloves and wash your hands immediately when done.