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Question of the Week: Can I mix my extracted breastmilk from different days?

"My son is 3 months old and I am exclusively breastfeeding him, but I just got back to work. Can I mix breast milk from different days?"


First of all, I commend you for continuing to breastfeed while you return to work. For many mothers, it is very difficult to continue breastfeeding due to work difficulties, schedules and the complexity of expressing milk at certain times.

The World Health Organization (WHO), along with health organizations such as UNICEF, the Academy of Nutrition and the American Association of Pediatrics recommend exclusive breast milk for the first 4 to 6 months of age. Breast milk offers the best nutrition for your baby. Studies indicate that babies digest breast milk better than any other formula. Breast milk contains unique nutrients that help your baby's immune system. Additionally, studies indicate that breastfed children have fewer allergies, ear infections, gastrointestinal problems. They also have a lower risk of obesity, diabetes and high blood pressure compared to formula-fed babies.

The International Milk League and Alba Lactancia Materna mention that if you can mix breast milk from other days or sessions. As long as both milks are at the same temperature and that the mixture is used within 24 hours. If you mix freshly expressed milk, which is warm, with frozen milk you can alter the nutritional properties of the milk due to the change in temperature. It is important to mention that these recommendations are based on healthy infants, born at term (not premature), for home use and not for hospital use. Studies indicate that babies digest breast milk better than formula.

How to mix and store breast milk:

  1. Wash your hands before expressing milk
  2. All milk must be dated before storage.
  3. Use containers washed with hot soapy water and rinse them
  4. Use food-safe glass or hard plastic containers. You can also use specially designed bags for breast milk storage
  5. If you are going to mix the expressed milk with other previously refrigerated or frozen milk, it is important that you first chill the milk in the refrigerator or under ice so as not to alter the nutrients of the breast milk.
  6. It is recommended that you store breastmilk in small quantities (1-2oz) so that you avoid wasting milk if your baby does not drink all of it.
  7. The milk that you put in the bottle and that your baby does not consume will have to be thrown away due to the risk of contamination, so try to put small amounts.
  8. Milk can be kept at room temperature (77F (25C) for 6-8 hrs. In an insulated bag with ice for 24hrs.
  9. Refrigerate (39 or 4C) for 5 days, be sure to store it in the back of the refrigerator to prevent it from thawing when opened.
  10. Freezer (0F -18C) 3-6 months
  11. If the milk has been frozen and thawed, it can be refrigerated up to 24 hours for later use. It must not be refrozen.

How to heat milk?

  • Warm thawed milk under warm running water or by immersing it in a bowl of warm water.
  • You should never let milk boil
  • Also do not use the microwave oven to heat breast milk
  • Shake milk and test temperature before use

How can I thaw breast milk?

  • Place the milk in the refrigerator to thaw slowly over 24 hours.
  • Place the container under cold water and slowly change the temperature to thaw it and come to room temperature

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