Pumping your breast milk is an awesome idea. Unfortunately, we live in a world where most of us can’t just stay at home with our babies until they are old enough to go to school. We must get back to work as soon as possible so that our household income doesn’t suffer. Therefore, we need to stop breastfeeding when we send baby off to preschool or daycare. If it weren’t for the breast pump, babies would have to switch to formula when mom went back to work. Luckily, that’s not the case. If you’re breastfeeding and need to leave your baby in someone else’s care, you don’t have to sacrifice the nutritious breast milk. You can pump the milk out of your breast and store it. That way, baby’s caregiver can feed it to your baby from a bottle just as she would formula.  

You should follow the instructions on your specific breast pump to ensure that you’re doing it correctly. Once the milk is in the bottle, it’s extremely important that you store it properly. Studies show that shaking the milk will actually cause the cells to separate, and this separation will make it harder for your baby to extract the nutrition that he or she needs. Additionally, many experts warn against freezing the breast milk for the same reason. The cold temperatures will cause a separation of the cells. However, many moms overlook this detail because freezing the milk is much more convenient. When you freeze breast milk, it can last for up to 12 months.

Essentially, you should treat your breast milk with care. When it is fresh out of your body, it is just as alive as the rest of you, and the cells are delicately strung together. By shaking it, heating it, or freezing it too much, you could disrupt the natural composition and make digestion more difficult for baby. Before you hand it off to your baby’s caregiver, you should also fill them in about proper care. If breast milk is mishandled, your baby might not get all of the nutrition he or she needs, which defeats the purpose of pumping in the first place. Most nursery school and daycare employees understand how to handle breast milk, but you should certainly let relatives and even your partner know about proper care. When they see the separation, there is no doubt they'lll be tempted to shake.

Source: Maria Marin et al: Cold Storage of Human Milk on Its Bacterial Composition. Journal of Pediatric Gastroenterology and Nutrition Volume 49 Issue 3 pp. 343-348 September 2009