Many breastfeeding moms decide to wean once they return to work. For some, it's an issue of the place and space. For others, the idea of adding time into their day to pump and store their milk is simply too stressful. Whatever your reasons are (recognizing that this is a very personal decision), just make sure you are 100% ready to wean.
Some women think they're ready and begin to wean, only to realize that they're not quite there yet. This can be tough on your body and on your milk supply, and -- as with everything in the breastfeeding experience -- being consistent is key.
Many working moms decide to wean away from the feeds that would occur during their workday, only to breastfeed when they're at home, which is considered partial weaning. It's an excellent option if your gut isn't telling you that it's time. (As a note, The American Academy of Pediatrics recommends that babies be exclusively breastfed for 6 months. After those 6 months, babies can be given complementary foods and breastfed. Breastfeeding may continue for at least 12 months or until "mutually agreeable.")
The best way to go about weaning to prepare for a return to work is to do it gradually. Ideally, you will start to wean your baby and your body well before your first day back. The number of feedings that need to be eliminated and the amount of weeks one has to wean before the return to work obviously varies from mom to mom. However, as a general rule, start to drop feedings or pumpings one-at-a-time, giving each dropped feed 3 to 4 days to settle in (being very conservative, you could wait an entire week). Gradual weaning will allow for your milk supply to decrease slowly and you should not be uncomfortable or have severe engorgement.
Obviously during this time, as breastfeedings are eliminated, the baby will need supplementation. If the baby is younger than 9 months old, he will most probably take bottles. If he is older, 9 months to 1 year of age, he may be able to take a cup. With planned weaning, many moms choose to stockpile their breast milk in the freezer well-ahead of time to make the transition easier for the baby.
More importantly, remember that whatever choice you make is the right one. You should not feel pressure from anyone to wean, whether at work or at home, and it is ultimately your decision.