Always thaw the oldest breast milk first. Remember first in, first out. Over time, the quality of breast milk can decrease.
There are several ways to thaw your breast milk:
In the refrigerator overnight.
Set in a container of warm or lukewarm water.
Under lukewarm running water.
Never thaw or heat breast milk in a microwave. Microwaving can destroy nutrients in breast milk and create hot spots, which can burn a baby’s mouth.
If you thaw breast milk in the refrigerator, use it within 24 hours. Start counting the 24 hours when the breast milk is completely thawed, not from the time when you took it out of the freezer.
Once breast milk is brought to room temperature or warmed, use it within 2 hours.
Never refreeze breast milk after it has thawed.
Source: CDC
Link: https://www.cdc.gov/breastfeeding/recommendations/handling_breastmilk.htm#SafeThawing
