Can You Mix Breast Milk and Formula in the Same Bottle?

No matter how many books you read, movies you watch, or childbirth classes you take, nothing quite prepares you for the moment you feed your baby for the first time. Watching them eat until their little tummy is full is indescribable, regardless of whether from the breast or a bottle.

The American Academy of Pediatrics (AAP) and the World Health Organization (WHO) recommend exclusive breastfeeding for the first six months of a baby's life, along with the addition of complementary foods starting at 6 months, and then as long as the parent and baby desire.

Yet, for some parents and babies, exclusive breastfeeding may not be possible, and formula is a healthy and safe alternative, either on its own or combined with breast milk. The great news is the benefits of breastfeeding aren't all or nothing.

Here, experts weigh in on what you should know about combining breast milk and formula, along with the risks, benefits, and safety precautions.

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When Mixing Breast Milk and Formula Makes Sense

Combination feeding refers to alternating between breast milk and formula or mixing breast milk and formula in the same bottle. While the benefits of breast milk are well-known, there are instances when a parent simply can't make enough supply to meet her baby's demand. There are many reasons why parents combination feed their babies. You might choose to combination feed if someone else takes care of your baby during the day while you work. You also might have a low milk supply, but you still want to breastfeed.

“In those cases, I say any breast milk is better than no breast milk,” explains Emily Wisniewski, MD, a pediatrician at Mercy Family Care in Baltimore. “Instead of having a family completely give up and switch over to formula, using both allows the baby to get some of the benefits of what breast milk offers while getting the same volume that the baby needs in order to grow.”

Premature babies may also benefit from a combination of breast milk and formula. Jeanine Hoelsken, a lactation nurse at Children's Hospital Colorado, says the hospital often provides formula with special additives for babies with complex medical issues and alternates those feedings with breast milk.

Also, parents transitioning away from breast milk may choose to mix breast milk with formula to extend the amount of time their baby gets breast milk while allowing their supply to diminish.

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Can You Mix Breast Milk and Formula in the Same Bottle?

The short answer is yes if the bottle is prepared correctly. Dr. Wisniewski says it's crucial to follow the formula manufacturer's directions when adding it to breast milk and always talk to your pediatrician or provider's office before changing your baby's diet.

Mixing breast milk and ready-to-feed formula

The easiest way to mix breast milk and formula in the same bottle is to start with ready-feed or premixed liquid formulas, explains Dr. Wisniewski. Simply combine them into a bottle and shake thoroughly. 

Mixing breast milk and powdered formula

Start by preparing the powder formula according to directions. Never use breast milk instead of water to mix the formula, says Dr. Wisniewski. She explains that doing so can throw off the nutritional balance and could be dangerous for your child. Once you've prepared the formula, then add breast milk to get the desired amount.

Benefits of Mixing Breast Milk and Formula

For a person struggling with breastfeeding or pumping, mixing breast mix and formula allows the baby to get the benefits of breast milk while ensuring they get enough nutrition to thrive. It can also help the baby transition from breast milk easier if the parent is heading back to work or the baby is under another person's care (or any other reason).

Mixing the two in the same bottle can also allow you to take advantage of your stored milk supply longer. According to the CDC, you can freeze breast milk for up to 12 months if the temperature is at or below 0℉.

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Risks of Mixing Breast Milk and Formula

Although mixing breast milk and formula in the same bottle is safe, Hoelsken recommends giving them separately. That way, you don't waste breast milk if the baby doesn't finish. Hoelsken says the goal should be to save every drop of breast milk you can, especially when you've worked hard to pump it into a bottle. 

Adding formula to your baby's diet may also cause you to breastfeed or pump less, diminishing your supply. And it could be unsafe for infants on a hypoallergenic or amino acid formula to add breast milk to their bottles if something in the parent's diet is causing an issue, explains Dr. Wisniewski. 

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How To Safely Store Mixed Bottles

Dr. Wisniewski says you should follow the CDC guidelines for safe formula storage if a bottle contains breast milk and formula. According to the guidelines, it's safe to use formula within two hours of preparation and one hour after the baby begins feeding. If the bottle hasn't been used, you can store it in the refrigerator for up to 24 hours.

Throw out any bottle remains that exceed the recommended time frames because the combination of the baby's saliva and formula can cause bacteria to grow.

When To See a Health Care Provider

Dr. Wisniewski and Hoelsken say to ask a health care provider for advice when:

Adding formula to your baby's diet after exclusively breastfeedingYour baby is vomiting excessively or losing weightRefusing to breastfeed or take the bottleAdding breast milk to hypoallergenic or amino acid formula

Additional reporting by Donna Murray, RN, BSN.

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