On the grand scale of things, there are lots of cats in need of homes, so adding more kittens is not ideal. From a health point of view, if the female is fit and healthy, and is an adult herself, then most have a healthy pregnancy and few problems giving birth. However, if you think your cat is pregnant, make some preparations such as registering with a vet (in case she has problems kittening) and read up on what to expect during the birthing process so you can spot if things go wrong.