Of course, your dog or cat is your baby, and shares your attention, affection and love. Now, you're expecting a human baby, who will share and dominate the bonds between you and your pet. It's normal to worry about how baby and pet will get along and adjust to each other. The chances of them accepting each other, even becoming good buddies, are in your favor. Some preparation can be made in advance.

DOGS

Put up a baby gate or close the door to the nursery immediately. Your dog will learn to stay out of, and possibly ignore, the baby's room. It's best for you to do this at first then later, gradually allow him to follow you into the room. He will learn that the room is not his “hang-out,” yet not completely off-limits. As your baby grows, they will become used to each other.

Have your dog meet other babies. Do this gradually so that each time he's around a baby, he becomes less anxious. By the time your baby arrives, he/she won't be a completely foreign object that takes you away. Your dog may meet the addition more casually.
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Be sure that your dog is well-trained, and obeys orders. A baby's behavior is unpredictable, and often startling. The dog must be the adult in this case. If the dog hasn't been trained, now is the time, before baby's arrival. If your dog is a male, have him neutered in plenty of time. Neutering calms a male dog and helps him to be well-mannered.

CATS

The suggestions for dogs apply to cats as well. The major difference is that a baby gate in the nursery's doorway is no obstacle. It is easy, even enjoyable for your cat to scale the gate, and by the way, the crib, as well. Protect the crib by covering it with a net.

If your cat usually sleeps with you, don't put the baby in your bed until you've removed the cat and shut the door.  

A rule for both animals is to keep their food and water dishes away from the baby.  They're toys to baby, and playing in them makes a mess and makes the animals jealous. If baby ever gets a hold of the pet food, it's a guarantee that he/she will eat it.

Be diligent in these matters and your pet and baby will develop a good, comfortable relationship. Your home will become harmonious once more.