Clean food-grade containers or unused breast milk storage bags are the best storage containers for human milk, especially if it's to be frozen and stored for weeks or months. Don't use bottles with the recycle symbol number 7. This means that the container may be made of a plastic that has the chemical BPA. Never use regular disposable bags, such as kitchen bags or those made for bottle feeding. Freezing may cause these to leak and break down. If using breast milk storage bags, squeeze the air from the top before sealing tightly. In general, place storage bags upright in another container or the milk may leak. But if the double zipper seal on the breast milk storage bag is reliable, laying the bag flat in the freezer will help the milk thaw faster later.

You may combine milk pumped from both breasts into a single container. Just carefully pour the milk from one container into the other. Store only 1 to 4 ounces per container. That way you won't waste any. It's easier to thaw a second container of milk than to watch your valuable milk be poured down the drain because it wasn't used. Label each collection container with the date and any medicines you have taken. It's okay to combine milk from different pumping sessions. Be sure it was pumped on the same day and the milk chilled before mixing it together.

The following guidelines are for healthy, full-term infants. Storage guidelines may be different for premature or high-risk infants. Talk with your baby's doctor for specific instructions.

Fresh breast milk contains the most active anti-infective properties, followed by refrigerated breast milk, and then frozen breast milk.

Unrefrigerated fresh milk may be left at room temperature of 77°F (25°C). But it must be used within 4 hours.

It's likely better to refrigerate fresh milk when it's not going to be used within 60 minutes. The refrigerator should be at a temperature of 40°F (4°C). Don't freeze milk for a high-risk baby if that milk has already been refrigerated for more than 24 to 48 hours.

If refrigerated milk won't be used within 4 days, freeze it for later use. Milk can be frozen for about:

• Up to 2 weeks if the freezer compartment is in the refrigerator. (You must open the refrigerator door to reach the freezer with this model.)
• 3 to 6 months in a freezer that is part of a refrigerator unit but has a separate door.
• 6 to 12 months in a separate, -0°F (-18°C) deep freezer.

To keep milk cool when a refrigerator isn't available right away, or to transport refrigerated or frozen milk, place it in an insulated bag or cooler with a frozen cold pack. It should be moved to (or back to) a refrigerator or freezer within 24 hours.