How to supplement with formula when you're breastfeeding

Whether you're struggling with low supply or wondering how to feed your baby when you head back to work, there are so many situations when you might need or want to supplement breast milk with formula. 

"Ultimately, we just want your baby to receive adequate nutrition," says Liz Donner, M.D., a pediatric hospitalist and member of the BabyCenter Advisory Board. "If that means supplementing with formula, that's perfectly fine."

Here's how to combo feed your baby, depending on what your goals are. 

Is it okay to supplement with formula?

Yes. Any amount of breast milk is beneficial, and it's okay to supplement with formula if that's what's best for you and your baby.

Health experts including the American Academy of Pediatrics recommend feeding babies breast milk exclusively until introducing solid foods around 6 months old. But parents may choose to supplement with formula for a variety of medical or personal reasons, such as a low milk supply or the challenges of pumping at work.

If you're supplementing because of supply issues, you might plan to go back to exclusively breastfeeding if your milk supply climbs again. Or, maybe you've decided to transition to formula before going back to work.  

How to start supplementing with formula

It's a good idea to cut back on breastfeeding sessions and add formula gradually, if you can. This will help you avoid issues like engorgement, clogged milk ducts, and mastitis.

For example, if you want to go back to work and nurse your baby in the morning and at night but provide formula for daycare, you would ideally cut out breastfeeding sessions one at a time, very steadily, until most daytime feedings are exclusively formula feedings. You could start by dropping one feeding every three to seven days. 

Try to be patient with the process, which may take weeks depending on how your baby does with formula and how your breasts adapt. As you replace nursing sessions with formula feeding, your milk production will slowly decrease. If you experience engorgement in the meantime, pump or manually express enough milk to feel more comfortable.

If you're still producing enough milk to make your breasts uncomfortable while at work, you could pump occasionally or manually express to relieve any engorgement – but not enough to stimulate more milk production. But if your overall goal is to reduce milk production, it's best to only remove enough milk to feel relief, not until the breast is fully emptied. Remember that the more milk you take out, the more milk your body will continue to produce day by day.

If you're supplementing because you're not producing enough breast milk, be sure to nurse your baby first, completely emptying your breasts, before giving your baby formula. This will provide your baby with the most breast milk possible while cueing your body to produce more milk.

When can I start supplementing with formula?

You can start supplementing at any time. However, if you’re looking to produce as much breast milk as possible, doctors and lactation consultants recommend waiting until your baby is at least 3 weeks old (if possible) to start supplementing with formula. This way, your milk supply and breastfeeding routine have adequate time to get established. 

If your baby has a medical issue, such as inadequate weight gain, your doctor or lactation consultant may recommend supplementing earlier than the 3-week mark.

Will supplementing with formula affect my milk supply?

Yes, your supply of breast milk depends on how much milk is removed from the breast. So the less often you nurse or pump, the less milk your breasts will produce.

If you supplement with one or two bottles of formula a week, the effect on your milk supply should be minimal. But if you supplement with formula regularly (for example, for one feeding a day) and don't pump for that feed, your milk supply will adjust to the reduced demand.

If you need to supplement for medical reasons but would ideally like to breastfeed exclusively at some point, make sure your doctor or lactation consultant knows this so they can help you develop a schedule for pumping that will help maintain your milk supply.

Keep in mind that you won't be able to use nursing as a method of birth control (the lactational amenorrhea method or LAM) if you're supplementing. For this method to be effective, your baby must be younger than 6 months old and you must breastfeed exclusively.

What are some signs that my baby needs supplemental formula?

Talk to your baby's doctor if you have any concerns about your baby's weight gain, growth, or eating habits. Here are some symptoms that warrant a call:

• More than normal weight loss in a newborn. Babies should lose no more than 7-10% of their birth weight in the first few days after birth. By 2 weeks, they should be back up to their birth weight.
• Fewer than six wet diapers in a 24-hour period once your baby is 5 days old.
• Fussiness or lethargy most of the time.
• Very short or very long nursing sessions. If your baby often nurses less than 10 minutes or more than about 50 minutes at a time, it may mean they aren't getting enough milk.

Here are reassuring signs that your baby's getting enough formula or breast milk.

How will supplementing with formula affect my baby?

Supplementing with formula may have little obvious effect on your baby, but you may notice:

• Your baby might start refusing the breast if you supplement regularly. A bottle can deliver milk faster than a breast, so if your baby's an enthusiastic eater, they might prefer a bottle.
• Your baby might go longer between feedings. That's because babies don't digest formula as quickly as they digest breast milk, so they're likely to feel full longer.
• Your baby's stool will be different. It will be firmer (about the consistency of peanut butter), be tan or brown in color, and have a stronger odor. Your baby will probably have less frequent bowel movements.

What's the best way to introduce a bottle?

If your baby has never taken a bottle before, they may need a bit of coaxing. Here are some tips:

• Mimic breastfeeding by cuddling and providing plenty of skin-to-skin contact. Switch sides, as you would if your baby were breastfeeding.
• Used paced bottle feeding, which is more like breastfeeding: keep the bottle horizontal, use a slow-flow nipple, and pause often during feedings.
• Try a preemie nipple. "I recommend using a preemie nipple when you first introduce your baby to a bottle, especially if you plan on still breastfeeding," Dr. Donner says. "This typically provides a flow rate more similar to that of the breast."
• Let someone else give it a go. If your baby refuses the bottle from you, they may be more receptive to taking it from someone else. Some moms find they even need to leave the house – so their baby doesn't smell them – for their baby to take a bottle instead of breastfeeding.
• Give your baby the bottle when they're just hungry, but not overly hungry and upset. Try to choose a time of day when they're usually in a good mood.

Read more about how to introduce your breastfed baby to a bottle.

If your baby is used to taking a bottle of breast milk, they won't mind drinking from the bottle. But they may not initially like the taste of formula – which doesn't taste like breast milk. (It's not as sweet.)

If that's the case, it's okay to combine breast milk and formula to help your baby get used to the taste. You might mix 3 ounces of breast milk with 1 ounce of formula, for example, and then gradually use more and more formula until your baby has made the full switch.

Never add powdered formula directly to your breast milk unless specifically directed to do so by a medical professional. This will over-concentrate the milk, leading to potential electrolyte imbalances. Mix the formula according to the package label first, and then mix it with breast milk. 

What's a supplemental nursing system and how does it work?

A supplemental nursing system (SNS) or supplemental feeding system is a way for you to nurse your baby and give them formula (or expressed breast milk) at the same time. The supplemental formula or milk travels along thin, flexible tubes that are taped (with paper tape) along your breasts to the ends of your nipples. When your baby sucks, they receive the supplemental liquid, along with any breast milk you produce.

The system allows your baby to continue to suck at your breast, avoiding any preference for a bottle, while also stimulating your milk production. An SNS is often used if a mother has a low milk supply, but it can also be used by partners and by adoptive parents.

Talk with your doctor or a lactation consultant if this is something you'd like to try.