How to Supplement with Formula While Breastfeeding

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Article last updated: September 23, 2023

Even with the best intentions to exclusively breastfeed, many women find themselves at one point or another, either needing or wanting to supplement with formula milk. In fact, worldwide, only 40% of all infants under the age of six months are exclusively breastfed. That means the other 60% are supplementing using breast milk and formula or exclusively formula feeding. 

Some women choose to do this type of combination feeding from the very beginning. In contrast, others start with exclusive breastfeeding and then find themselves needing to use a supplemental formula for various reasons.

Some choose to use a breast pump to draw their milk so babies can have pumped milk even when the mother is away. A mother’s breastfeeding journey may end early for reasons that may include: a delay in their breast milk supply coming in after birth, inadequate growth or weight gain in their infant, medical reasons such as food allergies, an overall low milk supply, returning to work, or other unexpected situations that prevent continued breastfeeding. If you feel like when you feed your baby they are not getting enough milk it might be a good idea to introduce formula into the mix. 

Moms need to understand how supplementing with formula works to ensure that it is done both safely and protects the mom’s milk supply, if her goal is to continue to provide breast milk.

Early Supplementation of Formula 

Experts agree that it is best to wait as long as possible before introducing a nursing supplement in order to establish a full milk supply. Generally, the mother’s supply is established around two months. However, in some cases, waiting to supplement may not be an option, or it may not be the mother’s preference. 

Reasons for formula supplementation in the hospital after birth include jaundice, low blood sugar, delay of milk coming in, excessive newborn weight loss, sore nipples, and the separation of mom and newborn for medical reasons.  

Since the early introduction of a bottle can interfere with long-term breastfeeding, other methods of supplementing a newborn are preferred. These methods include: 

• Use of a dropper or syringe 
• Use of a medicine cup or teaspoon 
• Use of a supplemental nursing system 

The first two weeks of lactation are an especially critical time in establishing a sufficient milk supply in the future. Even with supplemental milk, efforts should be concentrated on creating and protecting the mother's milk production, if the mother desires to continue breastfeeding. If the mother wants to continue breastfeeding it is a good idea to try and pump milk on supply and to give your baby formula until there is a resolution of issues.

Methods for Supplementing an Older Infant 

Many moms may think that combining formula with breast milk in the same bottle is the best way to supplement to get their infant used to the taste. While combining the two may seem like a good option for infant feeding, it’s generally not recommended for two reasons. 

First, if the formula feed combination is not prepared properly, it could potentially be harmful to the infant providing unbalanced nutrition. Second, if the infant doesn’t finish the bottle, the extra milk will have to be discarded within 2 hours, which is sooner than breast milk alone.  

In general it is not recommended to mix breast milk using formula. If the ratio is off the breast milk and formula may not contain all the needed benefits that each have on their own.

There are two methods generally recommended for supplementing breast milk with formula. First is what is often referred to as the top-off method. This is when a bottle of formula is provided to the infant either immediately after feeding at the breast or after receiving a pumped bottle of expressed breast milk.  

This method is popular among women who have low supply as it helps to ensure the infant is getting enough volume at each feeding. It also eliminates the potential of tossing perfectly good breast milk since it is not combined with the formula. We all know how valuable expressed breastmilk can be.  

One potential downside of the “top off” method is if the infant is being fed expressed breast milk in a bottle first and then formula. There are two bottles to prepare and then wash. 

The second method for supplementing with formula is providing a full feed of formula. In this method, mom would choose one or more feedings per day to provide formula only, such as at bedtime or for overnight feeds.   

Many moms prefer this method when they return to work and feed only formula while they are away from their infant. With this method, there is no potential for wasting breast milk that was not consumed, and only one bottle needs to be prepared and washed. 

If you do choose to supplement while breastfeeding, it's best to start slowly. Try just one or two bottles and gradually add formula as you need. How much you will need to supplement will vary depending on the situation and the baby's diet. 

Some infants may need just an ounce or two per day, while others may require 50% of their feeds from the formula. Your baby’s doctor, a pediatrician, or lactation consultant can help you determine how much is necessary.

How to Prepare Formula for Supplementing  

Some formulas are ready-to-feed, meaning they are in liquid form and fed to the infant as is. Other times, an infant formula comes in powder form and needs to be mixed. Powdered formula is not sterile, so it’s important when supplementing with formula to understand how to properly prepare it, to prevent the possibility of contamination. Always carefully read the preparation instructions written on the formula’s label. 

Steps: 

1. Wash your hands with soap and water. 
2. Add the amount of water listed on the formula instructions to the baby formula bottle. Use water from a safe source. It is not always necessary to boil the water first. 
3. Add the recommended amount of powder listed on the formula instructions. Always use the scoop provided with the formula. Adding an incorrect amount could make the infant ill. 
4. Mix the bottle by shaking or swirling thoroughly. 
5. Warming the formula is not necessary though many choose to do so. Warming should not be done in the microwave. To warm the bottle of formula, place the bottle in a mug or pan of warm water. Be sure to check the temperature before feeding the infant by putting a couple of drops of the formula on the back of your wrist.   

How to Bottle Feed a Breastfed Infant 

Many experts agree that an infant being offered a bottle, whether its formula or breast milk, should be pacedduring the feeding. The goal of pacing the infant at the bottle is to mimic the flow of breastfeeding and allow the baby to set the pace. Here are the key points to paced bottle feeding: 

• Hold the infant in an upright position. Do not feed lying down. 
• Allow the infant to draw the nipple in their mouths on their own. 
• Feeding at the bottle should take a similar length of time as a feeding at the breast. 
• Encourage frequent pauses while the baby drinks from the bottle to mimic the breastfeeding mother’s let-down patterns.  
• Switch sides halfway through the bottle feeding to promote proper eye development and prevent side preferences. 
• Stop the feeding if the infant shows signs of being satisfied. Do not force them to finish the bottle.

Additional Considerations When Supplementing While Breastfeeding 

There are a few things to note when supplementing breastfeeding with formula. It’s possible that the baby may initially refuse formula and/or a bottle if they have been exclusively breastfed for a while. Just keep trying. 

When introduced to formula, the stools of infants may change. They may appear less yellow and slightly more formed compared to the stools of an exclusively breastfed baby. This is normal and to be expected. 

Final Thoughts  

Making the decision to supplement breastfeeding with formula can sometimes be challenging, but mothers need to do what is best for themselves and their baby’s health. Breastfeeding does not have to be all or nothing. Any amount of breast milk an infant receives is beneficial and mothers do not need to wean from breastfeeding if they decide to supplement with formula. 

The content and advice provided in this article is for informational purposes only and is not a substitute for medical diagnosis, treatment, advice for specific medical conditions. Always consult a pediatrician to understand the individual needs of your child.