Supplementing an Underweight Baby

If a breastfed baby is gaining very little weight, not gaining, or losing weight due to not getting enough milk, the first priority is to make sure the baby gets more milk. There are several ways to increase a mother’s breast milk supply, however, these can take time and the baby may need more milk straight away. Sometimes parents are reluctant to supplement large quantities of donor milk or formula in case this undermines breastfeeding but medically indicated additional calories do not have to mean the end of breastfeeding.

This article

This article discusses a general care plan for supplementing an underweight baby while protecting breastfeeding—with the end goal of returning to full breastfeeding where possible. It is a companion article to read alongside Baby Not Gaining Weight and Understanding Your Baby’s Weight Chart. This general plan should never be considered a replacement for medical advice or a tailored care plan from your baby’s physician and your own IBCLC lactation consultant as it cannot take into account yours or your baby’s medical details. Please discuss the information in this article with the health professional caring for your baby.

Breaking the low weight cycle

When a baby is very underweight he can become too weak to breastfeed. This will mean he cannot “drive” or stimulate his mother’s milk supply properly. Milk production slows to meet the weak demand which causes even lower weight gain and so on in a cycle of low weight/low energy/low milk. Breaking this cycle involves checking baby’s health, restoring baby’s nutritional status and maximising the mother’s breast milk supply:

  • Medical checks. Rule out any underlying health issues for baby with your doctor or paediatrician to establish whether low milk intake is the only cause of poor weight gain. Stay in close contact with your baby’s doctor so they can monitor your baby’s recovery.
  • More milk. If a baby is substantially underweight they will need extra calories right away to protect their health, gain weight, and have more energy for breastfeeding. Doctor Marianne Neifert explains:

Providing appropriate supplemental milk to an underweight infant is necessary to prevent malnutrition, dehydration, electrolyte imbalance, cerebral infarcts, and other complications of inadequate breastfeeding.

  • Maximise breast milk supply. Although supplements may be needed short term, breastfeeding can be protected by increasing breast milk volume as soon as possible. With a more abundant milk supply a baby will be encouraged to breastfeed more readily (Neifert, 2001).

Supplementing an underweight baby

— A three step plan

The following care plan for rebuilding a baby’s weight while protecting breastfeeding is based on lactation consultant Pamela Morrison’s five step feeding plan 1 and Marianne Neifert’s triple feeding plan 2:

#1 Breastfeed

Breastfeed often, at least every two to three hours in the day and every four hours at night. Wake a sleepy baby to feed if needed—upright positions can help a baby stay awake to feed.

  • Latch and position. Check baby’s latch (the way they attach to the breast) and positioning with a breastfeeding professional, a good latch is important to drive a milk supply.
  • Offer both breasts per feed and use breast compressions. Rather than allowing baby to finish each side at their own pace, watch for active sucking and swallowing and help milk flow with breast compressions; a technique made popular by Canadian paediatrician Jack Newman. When active sucking stops despite compressions, switch breasts and repeat.
  • Limit the feed. Breastfeed for around 10-15 minutes each breast or 20-30 minutes total. A time limit prevents very long ineffective feeds. Long feeds where baby is flutter sucking or sleeping—but not drinking—do not stimulate a milk supply and perpetuate the low gain cycle. Long sessions of poor quality feeding also contribute to baby burning precious calories.

#2 Supplement

When baby isn’t swallowing at the breast any more, or after 20-30 minutes, stop breastfeeding. Top your baby up in the easiest way for you and your baby (see below). Use expressed milk first and then donor milk or formula as needed, use enough supplement so that your baby stops drinking of his own accord (see below for a guide to volumes). Settle your baby so that you can pump.

#3 Pump

Pump both breasts as soon as possible after you have breastfed, topped-up and settled your baby. Aim to pump at least six times per day if you can. Using “hands-on-pumping” (gentle light touch breast massage and breast compression while you pump) can stimulate more milk. Pump until the milk stops flowing and only produces drops of milk (around 10-15 minutes). Pumping both breasts at the same time (double pumping) can save time or some mothers may prefer to pump and massage each breast separately. Hand expressing after pumping can really help milk supply.3 Save any collected milk towards your baby’s next top-up, with the end goal of gradually pumping the entire supplement volume. See How Long Does Breast Milk Last? for storage information and How to Increase Milk Supply When Pumping for more pumping tips.

An hour goal

It is helpful to try to keep breastfeeding, topping up and pumping all within a reasonable time interval otherwise it can feel too difficult and time consuming for the mother. Aim to breastfeed for around 20-30 minutes, top baby up to satiety (10-20 minutes), then pump (10-15 minutes) all within an hour. Marianne Neifert recommends:

The mother should pump for 10 to 15 minutes using a dual collection system to drain both breasts simultaneously. The high-fat, calorie-dense hindmilk obtained with the breast pump may be used to supplement the infant, with additional formula as required. This triple-feeding regimen—breastfeeding for approximately 10 minutes per breast, supplementing the infant to satiety, and pumping for approximately 10 minutes—should not exceed 1 hour.

A hungry baby, with tight fists, a frown and bent elbows
A hungry baby, note tight fists, frown and bent elbows

Frequently asked questions

Is my baby really hungry or just small?

The characteristics of a hungry baby can sometimes be mistaken for being either very fussy, very “good” or just small/petite. See Baby Not Gaining Weight for a summary of behaviours you might notice in a hungry baby and check Understanding Your Baby’s Weight Chart. Your health professional and/or IBCLC lactation consultant can help to interpret your baby’s weight.

Why can’t I just breastfeed more?

If breastfeeding has led to your baby not gaining weight, simply doing more of the same, in the same way, is unlikely to help until your baby has more stamina and the reasons for low gain/low milk have been found and addressed. Supplements may be needed to provide enough food, and pumping will help to jump-start your milk supply. There are a couple of situations to be aware of:

  • If a baby is only slightly underweight but otherwise healthy or for whom growth faltering is a very recent event, appropriate breastfeeding management measures may be sufficient to increase a mother’s breast milk supply. Always be guided by and stay in close contact with your baby’s doctor or health visitor. If there is no extra weight gain after two to four days, supplements will be needed (Morrison, 2011).
  • The newborn baby who has lost more than 10% of their bodyweight after birth, is at risk of dehydration or breastfeeding-associated hypernatremia (high sodium levels in the blood). This is a serious condition and babies will need to be assessed by a doctor so that their electrolytes (e.g. sodium levels) can be checked and carefully corrected and supplements provided under medical guidance.4 56

How can I make more breast milk?

The more often milk is removed from the breast and the more thoroughly, the more milk will be made. An underweight baby is not very good at this, help him stimulate your milk supply by:

Review reasons for low supply

In some cases there may be medical reasons for low milk supply, review possible causes for low milk/low weight gain with a breastfeeding expert.7

For more information see How to Make More Breast Milk or follow the advice tailored for you by your IBCLC lactation consultant.

Do I have to pump? I can’t pump much

Once a baby catches up and is back to the healthy weight-for-age they should be, a baby is often better able to drive his mother’s milk supply. Until this time, pumping with an efficient pump can really help to stimulate your milk. Try not to be disheartened if you only get 10-20ml from each breast or less when you first start pumping, you can build on this. The process of pumping an empty breast is putting in the order for more milk tomorrow.

Keeping a record

It can be helpful to keep a record of volumes of breast milk expressed each day and volumes of formula given so you can gauge progress (over time breast milk will go up, formula will go down). Charting the number of wet and dirty nappies can also help gauge whether your baby is getting enough milk, alongside weighing your baby regularly.

What supplement should I give?

The first choice for a supplement is always mothers’ own expressed breast milk. However, if a mother is unable to pump enough expressed milk to satisfy her baby, she will need to choose between donor milk where available or using baby formula. Always feed any expressed breast milk first, then donor milk, and finally formula. It is thought that mixing human milk and formula into the same container should be avoided as there are concerns that direct mixing could interfere with the antibacterial benefits of breast milk and mixing could lead to wasted breast milk if baby doesn’t finish the bottle.89 See Supplementing With Formula for more information.

How much supplement should I give?

A general guide used for overall milk intake normally is 150–200ml/Kg/day.10 How much supplement an individual baby needs will vary with their age, weight, frequency of feeds and depending how much breast milk they get. Krugman and Dubowitz 11 say that infants recovering from faltering growth (failure to thrive) need 150% of the intake for their expected, not actual, weight for catch-up growth. This means the amount of top-up needed may be much higher than expected for a while. A top-up at each feed might be anything from 30ml to 120ml or even more.

Pamela Morrison 12 explains that while 180ml/kg/day above 10 days of age is a normal intake for a healthy baby, some babies will start taking surprisingly large volumes while they catch up. Be guided by a baby’s appetite by offering enough supplement until they stop drinking because they are full. She explains:

In consultation with the baby’s paediatrician it may be appropriate to feed the baby up to 280–300 ml/kg/day while s/he achieves a “catch-up gain”

If your baby doesn’t seem hungry

A very underweight baby may find it hard to drink much at first as they may have become used to very small meals and they might bring back some of the top-up as spit up. If so, try offering smaller volumes more frequently and then follow baby’s appetite as it picks up. If your baby is not showing hunger cues Wambach and Spencer13 suggest aiming for a minimum supplement of 100ml/kg/day divided into eight to twelve feeds. After one to two days increase the supplement gradually until the baby starts to demand his feeds.

My doctor says to give two bottles of formula per day

Your experienced health professional may prefer to prescribe set volumes of top-up to be certain your baby is getting what he needs—particularly if your baby is not showing good hunger cues. If your health professional recommends, let’s say, two 150ml (5oz) top-up bottles per day or 300ml/10oz per day this is the same as topping up 50ml after six day time breastfeeds (50 x 6 = 300ml per day). Topping up smaller amounts to make up the same total can be more protective of breastfeeding because:

  • Baby is not overloaded in one meal which may cause him to sleep for a long time missing potential breastfeeds
  • Baby is able to satisfy their appetite throughout the day not just twice a day
  • Too much milk in one go could be brought back as spit up.

In practice, find the pattern that works for you and keeps your baby well fed—monitor baby’s weight gain closely. If a breastfeed is missed out, remember to pump during the interval.

How should I give the supplement?

It is important to find an easy way for the low weight baby to take his supplement. Options include

  • Cup feeding—baby must be awake and alert which can be problematic with a very weak and sleepy underweight baby
  • Supplemental tube—either at breast or by finger-feeding. This may work for some babies but may be too difficult or slow and consume too much energy for others who are very weak
  • A bottle can be the most efficient and least stressful feeding method for an underweight, sleepy baby until they have gained their expected catch-up weight (Neifert, 2001). There are several ways to make a bottle feed more like a breastfeed and reduce nipple confusion but avoid overly pacing a feed for an underweight baby, their appetite needs encouraging!

bottle feeding an underweight baby

My lactation consultant says supplement first, then breastfeed?

The three step plan above discusses breastfeeding first and then supplementing your baby. Alternatively some lactation consultants favour giving a limited amount of supplement before breastfeeding.14 The rationale being that the baby receives some calories to give them energy to breastfeed well and then baby associates the breast with feeling full as they fall asleep. This may work well for some babies. It can be difficult to gauge the top up volume before a breastfeed so that a baby is well fed yet not too full or sleepy to breastfeed efficiently. Another variation is to start and finish at the breast with the top up in the middle. As long as an underweight baby is getting the additional calories they need, is still getting plenty of chances to breastfeed, and mother has time to pump, parents can find what works best for them.

When can I get back to exclusive breastfeeding?

The time taken to get back to exclusive breastfeeding will vary depending on a number of factors including how well your milk supply rebounds, the age of your baby and how underweight they were. Some mothers will find supplements are only needed for a few weeks or months while others may still need to top up until solid foods become a regular part of baby’s diet. If supplements are stopped too soon, a baby’s weight can falter again. As a mother’s breast milk supply increases and baby has more stamina to take more direct at breast, baby will gradually take less and less supplement after they have breastfed until it isn’t needed. Marianne Neifert suggests continuing to pump after breastfeeds until the baby is gaining weight well with exclusive breastfeeding, and then gradually reduce pumping sessions.

How quickly will my baby gain weight?

Although this will vary between babies, once they are getting more milk it is common for an underweight baby to have a few days of weight gains up to 120g a day while they replenish body fluids (Smillie, 2016). They will usually continue to steadily gain weight and gradually move up one or more centile lines on their weight chart until they reach a healthier weight for their age.  The baby’s initial ravenous appetite will settle down again into the normal pattern of weight gain for their age once they have caught up.  See Understanding Your Baby’s Weight Chart and Baby Not Gaining Weight to know what to expect as time goes on and keep a close eye on your baby’s weight gain as they recover from faltering growth.


When a baby has growth faltering due to not getting enough breast milk, a plan of care that includes breastfeeding, supplementing and pumping ensures baby is well fed while protecting the breastfeeding relationship. Such a plan should always be under the guidance of your baby’s medical team who will monitor your baby’s recovery and weight gain. By finding the reasons for low milk intake and starting measures to maximise a milk supply, supplements do not have to mean the end of breastfeeding. Supplementation should not be withdrawn too soon or baby might start to lose weight again. Once a baby is back to the weight he should have been, and the original causes for low milk supply addressed, exclusive breastfeeding can often continue. Occasionally a mother may not be able to provide a full milk supply for her baby.

Thank you

Special thanks to Pamela Morrison IBCLC 15 who first introduced me to this plan and shared her extensive experience with low weight gain babies making this article possible.