Hi Angela and welcome!
I have never heard about this cat in the bed theory

. I'm trying to get pregnant myself and I have two cats in my bed

My guess would be that the nurse is thinking about toxoplasmosis (can you get back to her and ask her?). Toxoplasmosis is a disease caused by a microscopic parasite. If a pregnant woman becomes sick it can harm the embryo/fetus and may cause a miscarrige.
Now, cats can also get infected with toxo and if they are, they shed the parasite in their feces. Therefore, most doctors would advise pregnant women to a let someone else take care of the litter box or at least use protective gloves.
Unfortunately, some doctors will still tell a couple to get rid of the cat. This is totally unnecessary! The only way for a woman to become infected is by direct contact with contaminated feces!
Now some more facts:
- Most people get infected with toxo at some stage of their life. Once you've got it you develop an immunity and can't have it again (this is true to almost everyone, though I guess there may be rare exceptions). You can have a blood test done to check whether or not you're immune to toxo - highly recommended before a pregnancy.
- The most common way of getting toxo is by being in contact with raw meat (either eating or preparing it). The second most common is working in the garden (it's in the soil). I still haven't heard of a doctor telling a pregnant woman not eat a medium-rare steak

- Cats are not constantly infected with this parasite
. They become infected by eating raw meat (possibly prey). This is one reason why we shouldn't feed our cats with uncooked meat.
Here's a good link for information about toxoplasmosis:
http://www.toxo.org.uk/
I hope my post is not too overwhelming for a first reply

Enjoy your cat!