For information on selecting the appropriate pump, see Collecting and Storing Breastmilk. You will want to purchase or rent your pump no later than three weeks before returning to work. Even if you are at home with your baby for the first several weeks or months, it is helpful to have the pump to store up some milk to have on hand when you start working, to introduce baby to bottles so you can be sure he will take them when you leave him with a care provider, and to give you time to familiarize yourself with the operation and cleaning of your pump, as well as get an idea of how long each pumping session is likely to take. Storing up some milk beforehand in the freezer is a good idea, because even with a good pump, the stimulation you get while separated from your baby will be less than you are getting while you are together. Also, there is no pump on the market that is as efficient as the baby at removing milk and stimulating your supply. When you add in the fact that leaving your baby often creates stress, it isn't surprising that many mother's milk supply will drop off somewhat when they return to work/school. You may have days that are more hectic than usual, or you just may not feel good physically some days. Your baby may go through a growth spurt, and demand may temporarily exceed supply. In the beginning, you won't be sure exactly how much to leave for a feeding, although you will quickly find out how much he takes each day.
For all these reasons, you will feel better if you have some extra milk stockpiled in the freezer. You don't need to have gallons on hand, just enough for a few feedings. Pump after feedings for five minutes, or on the other side when your baby takes one breast at a feedings (your supply will be more plentiful in the mornings) and store the milk in 2-ounce portions. Try to have at least 12 ounces on hand. If you have strong feelings about not wanting your baby to have any formula at all, or if he is allergic to formula, you may want to have a little more stored up.
Selecting a care provider is seldom easy. Leaving your baby will be much less stressful if you feel really comfortable with your child-care situation. Probably the ideal provider is a family member, like dad or grand-mom. If this isn't an option, you may want to look for a mother who provides child-care in her home for one or two children, or a nanny who can come into your home. Putting a baby (especially a tiny infant) into a day care center with multiple infants is probably the least optimal situation, but if that is your only choice, talk to other parents whose children are enrolled. Look for a center with the highest possible ratio of adults to infants. Drop in unexpectedly and see how things operate when they aren't expecting a visit. Be sure to let the care providers know that you are nursing. If they aren't familiar with handling human milk or nurturing nursing babies, look elsewhere or share the information in Caregiver's Guide to the Breastfed Baby with them. Take comfort in the fact that breastfeeding protects your baby from many of the nasty germs that seem to get passed around day care centers.
Try to do a "trial run" the week before you return to work/school. Leave the baby with his caregiver and go to wherever you will be pumping. This will give you a chance to scope out the situation:
• Do you have an electric outlet?
• Do you need an extension cord?
• Do you need to find out which office space will be available, and when?
• Do you have access to hot water to clean your pump parts?
• Is there is refrigerator, and if so, can you store your milk in it if needed? etc, etc.
You should also let the caregiver feed the baby while you're gone, so you can see how he will take the bottle, and get an idea of how much he will take at a feeding. Leaving him for the first time is stressful enough, but will be easier if he is left in a familiar environment.