Having a new baby join your home is a change for everyone there. It is no different for pets that you have. Indoor pets are, especially, affected by the new bundle of joy. They may see a new baby as an intruder to their territory. There are some things you can do to get your cat ready to share the home with a new child.
Before you begin your training make sure that your cat is healthy. A check-up with a veterinarian is a good idea if your pet hasn't had one lately. A couple other basic things to do are to play sounds of a baby to let your pet get used to the sound of a newborn human and to let him or her explore the nursery. Don't let the cat set up camp in the nursery, though. This will make the situation worse when the baby starts using the room and displaces the cat.
If the child isn't born yet and the pregnant woman is the person that does most of the caring for the cat, the responsibilities should be shifted before delivery. Cleaning the litter box should have already been a duty given to someone else for health reasons. Feeding and playtime should also be taken over by someone else in the house. This will keep the cat from feeling as jealous of the baby taking all of the mother's time after the child comes home.
Get your cat used to the sounds and smells that come with having a baby in the house. Set up the baby swing and let it swing empty. Put some baby powder on a couple blankets and play with some baby toys. Allow your pet to associate these sounds and smells with you or the other caregivers before the child is in the picture.
Crib covers are available to keep the cat from getting into the crib and thinking that is his or her new bed. These can be used after the child comes home, as well. Another idea is to replace the door on the nursery with a screen door. This will allow you to keep the cat from getting into the room but still allowing you to hear if the baby is awake or upset.