One of the things cats cherish most is routine; it makes them feel safe. When families have babies, it turns a cat's world upside down. Babies smell different, sound different, and look different. It's important you take steps, prior to the arrival of your new family member, to prepare your cat by pre-exposing it to what's to come.
Here are some ideas that will help your cat:
Rub your body with the baby oils, lotions and other products you'll be using so your cat gets used to those scents.
I-calm cat is a sound system that is engineered specifically to the range your cat hears. They produce a Noise Phobias track that includes baby noises - this will help to desensitize them to baby sounds.
Scatter around blankets and the baby's toys so the cat can get familiar with those sights and scent them with their own smells.
Be sure to go the extra mile to keep the amount of play time, grooming and petting you give your cat consistent. A new baby takes a lot of time and changes your schedule, but try to keep your cat's schedule consistent. Be sure to keep the feeding times and litter cleaning consistent.
If you have a friend with a baby, ask them to come visit regularly so your cat gets familiar with the sight and movements.