Most of the time a pregnant cat will be able to deliver and tend to its kittens at home without needing much or any human interaction. But nature isn't always perfect. After the litter is born you'll want to keep some distance so as not to upset the female who may be overly protective of her babies but you also want to make sure the animals are doing ok. A mother cat who isn't feeding her kittens is a definite sign of trouble.
What to Do if A Mother Cat Isn't Nursing?
The short answer is you need to get the mother cat and kittens to the vet for a checkup, without delay. It could be that the mother has mastitis or some other condition that makes nursing painful. If that is the case, the kittens will need to be hand-fed until the mother cat is recovered. Only a trained veterinarian will be able to tell why a queen has stopped nursing.
Bottle Feeding Kittens
Bottle feeding kittens sounds adorable but it's also round the clock work. If you're up to the task, you'll need to get some small nursing bottles and a supply of kitten milk. One brand is KMR, which is available online or at stores such as Petco. Your veterinarian may be able to help with those, or you could check with your local pet supply stores. In an emergency, you can create a reasonable substitute for the mother cat's milk, with this recipe for "Kitten Glop." Your vet will be able to tell you how much and how often you should be feeding your litter.
I also have an article on feeding newborn kittens that should help get you started.
If The Mother Rejects The Kittens
While it's not common occasionally Queens will reject certain kittens or even a whole litter. This can often be a sign of ill health in the kittens or litter. Kittens that have been rejected can survive with human intervention.
If the mother cat has completely rejected the kittens, they will need to be kept warm. Chilling at this tender age can be quickly fatal to kittens.
Other resources can be found in my article on Post-Nasal Care for a Queen and her Kittens.
Where To Get Help
Caring for special needs kittens maybe more work than you feel you can't handle. If so you'll need to find a local rescue group that might be willing to foster the kittens. Your veterinarian or local animal shelter should be able to help you locate such a group.
I hope after this experience, you will strongly consider spaying your female cat. It's really the best solution for her health, and for avoiding future crises such as you are presently experiencing. If she does nurse her kittens after veterinary care, she can be spayed as soon as they are weaned, as early as six to eight weeks after birth.