Some do, some don't, the key is selective breeding and holding animals back for their temperament.

If an animal nibbles as a greeting or warning it's ok however if the animal truly bites hard and you need to do cage maintenance it's gonna get hold real quick pregnant or not.

Now if YOU mess around with her non stop and without a good reason then the problem is not her but you.

I can handle all of mine any time, pregnant, with young babies etc.