Can You Add Fresh Breast Milk to Previously Collected Breast Milk?

How to Combine Fresh, Room Temperature, Refrigerated, and Defrosted Breast Milk

Breast pump next to baby
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If you pump, or hand express, your breast milk at different times during the day, you may be wondering if you can combine the breast milk from those different collections into one storage container, especially if you're only getting a small amount of breast milk at each session. Combining the breast milk from different pumping sessions into one container can make storing and transporting your breast milk easier, and it can certainly save space in your refrigerator or freezer.

Well, if you follow the proper guidelines, you can collect breast milk at different pumping sessions on the same day and place it together into the same container. Here are the guidelines and what you need to know.

You Can Safely Combine Breast Milk If:

  • You have a healthy, full-term baby.
  • You are expressing and collecting breast milk for your own private home use.
  • Your hands, pump, and collection containers are clean. 
  • The breast milk that you are combining has been collected on the same day. 

When You Should NOT Combine Breast Milk

  • If your child is premature or has a compromised immune system, you should not add fresh breast milk to any previously collected breast milk. When breast milk is collected for sick or premature infants, it should be sealed and stored immediately. Once sealed, the collection containers should not be opened again until they are ready to be used. Keeping the containers sealed will help to prevent any contamination of the breast milk or the container.
  •  If you will be bringing your breast milk to the hospital for a sick or premature child, or you are collecting breast milk to donate to a human milk bank, follow the guidelines for milk collection and storage that you are given.
  • If you are not in a clean environment, or you are not able to wash your hands before collecting your breast milk, do not add that milk to a previous collection. If you believe your breast milk has been contaminated, it's best to pump and dump that session than to compromise your child.
  • Do not add breast milk that you pumped today to a container of breast milk that you pumped yesterday or last week. 

Can You Add Fresh Breast Milk to Previously Pumped Room Temperature Breast Milk?

Freshly pumped breast milk can be added directly into a bottle of room temperature breast milk as long as the previously collected room temperature breast milk has not expired. Breast milk can stay out at room temperature for about 5 to 8 hours depending on how warm or cool the room is. If you have a few pumping sessions within that time span and wish to combine the milk that you pumped, you can.

When adding breast milk from different pumping sessions to the bottle of room temperature breast milk, you should consider all the breast milk to be as old as the oldest pumped milk once you combine them. So, if you add breast milk that you just pumped to milk that you pumped 3 hours ago and left out at room temperature, the entire container, including the fresh breast milk, should be considered 3 hours old.

Can You Add Fresh Breast Milk to a Bottle of Refrigerated Breast Milk?

You can add more breast milk to a container of refrigerated breast milk, but it should not be freshly pumped body temperature breast milk. If you'd like to add your most recently pumped fresh milk to a bottle of already refrigerated milk pumped on the same day, you need to cool it down.

First, place the fresh breast milk into the refrigerator for 30 minutes to an hour. Then, once it is cool, you can add it to the other container of refrigerated milk.

Can You Add Freshly Expressed Breast Milk to Defrosted Breast Milk to Feed Your Baby?

If you have defrosted breast milk and fresh breast milk that are at about the same temperature, you can put them together in the same bottle to feed to your baby.  However, freshly expressed breast milk is a little better than previously frozen breast milk, so it's more beneficial for you baby to get every drop of your fresh breast milk.

It might not be as convenient, but it's better to give the fresh breast milk first. Then, finish the feeding with the defrosted milk. This way, the fresh breast milk will not be wasted. If there's any left over at the end of the feeding, it will be the defrosted breast milk that gets thrown away.

Can You Combine and Store Fresh Breast Milk and Defrosted Breast Milk?

Do not add freshly expressed breast milk to defrosted breast milk if you plan to store it. Once you thaw out frozen breast milk, it must be used or discarded. It cannot be refrozen. If you'd like to store your fresh breast milk, keep it separate from the defrosted milk. 

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Article Sources
  • Academy of Breastfeeding Medicine. Clinical Protocol #8: Human Milk Storage Information For Home Use For Healthy Full-Term Infants. 2004. Princeton Junction, New Jersey.
  • American Academy of Pediatrics. New Mother’s Guide To Breastfeeding. Bantam Books. New York. 2011.
  • Lawrence, Ruth A., MD, Lawrence, Robert M., MD. Breastfeeding A Guide For The Medical Profession Seventh Edition.  Mosby. 2011.
  • Riordan, J., and Wambach, K. Breastfeeding and Human Lactation Fourth Edition. Jones and Bartlett Learning. 2014.