Mothers have successfully fed their children for thousands of years of human history without understanding how it works. It’s a bit like driving a car – as long as it’s working well, you don’t need to know what is going on under the bonnet!
If you are having breastfeeding problems, such as low milk supply or too much milk, or are wondering why your baby’s feeding pattern is different from what you expected, it can help to understand more about the science of lactation (producing milk).
Most of the research that has ever been done on breastfeeding and human milk has been done in the last few years. It is a very exciting time for lactation science. Lots of things that experienced mothers have always known turn out to have a clear basis in the anatomy of the breast and the science of milk production, for example:
- Each baby and mother pair is different
- Healthy babies are the best judges of when and how to feed
- The way to make more milk is to remove more milk
Getting ready – the developing breast
Breast development starts around the age of 10-12 years. From puberty, the breast grows a little with each menstrual cycle. Inside the breast, the branches and buds that will become milk ducts and alveoli (milk storage sacs) start to develop. Radiation or trauma to the chest at this stage can have an impact on later breast development.
Lactation begins – pregnancy
For many women, tender breasts are an early sign of pregnancy. The breast completes its development during pregnancy, and milk production begins in the middle trimester. If a pregnancy ends after 15-16 weeks, colostrum (early milk) will be present. Some women choose to express colostrum in the last few weeks of pregnancy. This is recommended for women with diabetes, whose milk may be a bit slower to increase and whose babies may have low blood sugar after birth.1 Colostrum expressed before birth can be stored, to be given to the baby if they need extra milk. Mothers with high-risk pregnancies, or who are concerned about having enough milk, may also choose to express colostrum in the last weeks of pregnancy. It is usually recommended not to start before 36 weeks, unless premature birth is imminent. The amount of colostrum you can express before birth does not predict your ability to make enough milk afterwards.
After birth (day 1-3)– lactation takes off!
During pregnancy, milk production is held in check by the hormone progesterone, produced by the placenta. Once the baby is born and the placenta is delivered, levels of progesterone drop rapidly; this, coupled with high levels of prolactin, allows lactation to begin fully.
Retained placental fragments can reduce or even stop milk production. If you have unexplained low milk production and are still bleeding heavily or irregularly after you would expect to have stopped, check with your midwifery team or doctor. Removal of the last fragments of placenta will usually allow milk production to resume normally.
Mothers typically start to notice the signs of “onset of copious milk production” (also known as milk “coming in”) two or three days after birth. For a day or two you might experience:
- Breast tenderness
- Increase in breast size
- Mild fever
The discomfort you feel is primarily due to tissue swelling, in response to the sudden increase in milk volumes. Don’t panic – your breasts won’t feel like this for long! As your breasts adjust to making the amount of milk your baby needs, the swelling will settle down. If feeding your baby or expressing milk doesn’t quickly help you feel more comfortable, there are other steps you can take to deal with engorgement.
Onset of copious milk production can happen a bit more slowly:
- For first-time mothers
- In women with diabetes
- In women who are obese (BMI over 30)
- After a more difficult birth
To make milk, remove milk (day 3-4 onwards)
Until day 3-4, milk production is controlled entirely by hormones and will happen automatically, whether or not you go on to breastfeed. After day 3-4, another mechanism comes into play. Milk will only continue to be made if milk is removed from the breasts. The more milk that is removed, the more milk will be made. This enables your body to adapt to the number of babies you have. With enough milk removal, it is possible to exclusively breastfeed twins or triplets! If you do not breastfeed or express milk at all, your milk production will shut down within about two weeks after birth.
Remove milk early
The amount of milk that is removed in the period immediately after birth is important for later milk production. Research on lactation after premature birth has shown that starting to express milk within an hour of birth, compared with starting at six hours, is associated with more milk six weeks later.2
If your baby has any risk factors for not being able to feed effectively at first, such as being:
- Small for gestational age
- Separated from you
then early, frequent milk expression will help to ensure plenty of milk to meet their needs, now and later. You can see a useful video about this here:
Parents who have risk factors for low milk supply can give their milk production the best possible start by removing milk early and frequently after birth.
Risk factors include:
- Previous history of low milk production
- Previous breast radiation or surgery
- Polycystic ovary syndrome (PCOS)
- Thyroid problems (hypo- or hyper-)
- A history of infertility with hormonal cause
- Unevenly sized, widely spaced breasts, with little or no changes during or after pregnancy
- Obesity (BMI over 30)
People with these risk factors may be able to make a full or partial milk supply – you never know what you can do until you try! If you are not producing all the milk your baby needs, you can still enjoy a close, happy feeding relationship with your baby. You can read more about how to use donor breastmilk or formula milk to support breastfeeding here.
Some mothers who need to supplement their own supply with donor milk or formula milk in the early months are able to reduce or eliminate the supplementary milk after their baby starts complementary foods, at around six months, going on to happily breastfeed alongside solids.
Remove milk often
After their first feed and a few hours of sleep, full-term, healthy newborn babies feed frequently, around the clock. Most babies need to feed at least 8-12 times in 24 hours in the early weeks, suckling and swallowing actively at each feed, to get enough milk and stimulate their mother’s milk production. If your baby is not feeding as often or energetically as this yet, it is important to express your milk, if your goal is a full milk supply.
As milk builds up in the breast, a protein in the milk, known as the “Feedback Inhibitor of Lactation” (FIL), begins to slow down milk production. Breasts that are full make milk slowly, and eventually not at all. Breasts that are well drained make milk quickly. This is why, if you are trying to maximise milk production, it is important not to wait until your breasts feel full before feeding or expressing. Over time, this will reduce milk production.
Different breasts, different feeding patterns
Storage capacity is quite a new concept in breastfeeding, and it explains a lot of things that mothers instinctively knew, but were not in the textbooks!3
A mother’s storage capacity is the amount of milk that her breasts can hold between feeds. It is not related to breast size and it is not related to the total amount of milk that a mother can make each day.
To understand storage capacity, let’s assume that:
Alisha and Beth both have 3 month old babies and well established milk supplies.
Alisha’s breasts can hold 75ml of milk and Beth’s breasts can hold 150ml of milk.
Both their babies need about 750ml of milk per day (this is an average amount. Some babies might take as much as 1200ml per day).
Alisha’s baby needs to feed at least 10 times in 24 hours to get this amount of milk, while Beth’s baby could get the same amount of milk in only five or six feeds. [Feeding this infrequently is not common – it is at one end of a wide spectrum of feeding patterns!]
Both babies are getting as much milk as they need and growing well, but they have very different feeding patterns. What happens if Alisha and Beth are told that their babies “should” both be feeding eight times in 24 hours?
Alisha’s baby is hungry and miserable. She is no longer getting enough milk and if this continues, Alisha’s milk production will slow down due to the action of FIL in the full breast. It might be hard to increase milk production again, after the early weeks, when milk supply settles at a stable level.
Beth’s baby is irritable because his mother keeps trying to feed him again when he doesn’t want any more milk!
Both Alisha and Beth can successfully breastfeed their babies as long as their feeding pattern works for their milk storage capacity.
Beth, with her larger storage capacity, has more flexibility in her feeding patterns. Her baby is likely to have fewer feeds per day than Alisha’s, is more likely only to take one breast per feed and may start sleeping for longer stretches earlier. She could choose to feed more often, if her baby wanted to.
Alisha has less flexibility in her feeding patterns because if she doesn’t feed often enough, her breasts fill up and she doesn’t have room to make more milk. Her baby is likely to feed frequently day and night during the exclusive breastfeeding period and may need to feed on both breasts at most feeds.
Most babies need to feed at least 8-12 times in 24 hours and it is important to ensure frequent feeding during the early weeks, when milk production is becoming established. After the early weeks, most babies spend less total time feeding, as efficiency improves. Some babies will also significantly reduce the frequency of feeds.
Most mothers never need to worry or even think about their breast storage capacity, because their babies are brilliant at working it out for them! Full-term, healthy, thriving babies are able to choose their own feeding pattern that works with their mother’s breasts and their own needs as they grow. . If your baby is growing well and seems contented, their feeding pattern is working well for them.
Fat in milk
This is a topic that often worries parents, because of poorly understood information circulating among families about the differences between “foremilk” and “hindmilk”.
We know from research that:
- The breast makes milk fat at a stable level. The types of fat in milk are somewhat related to the types of fat in the mother’s diet, but the amount of fat is not related to her diet.
- The milk available at the start of a feed (often referred to as foremilk) has a lower level of fat than the milk at the end of the feed (often referred to as hindmilk). As the breast is drained, fat levels in milk increase as more fat droplets are “squeezed” to the front of the breast and out through the nipple.
- The level of the fat at the start of one feed depends on how long it has been since the last feed. The longer the interval between feeds, the lower the level of fat at the start of the next feed.
Parents often worry, or are told, that their baby might not get enough fat (this is often described as “getting too much foremilk”)
Research shows that full-term, healthy, thriving babies are brilliant at balancing their own diets. They will stop feeding when they have had enough calories. When fat levels in milk are higher, they will take less milk. When fat levels are lower, they will take more. The varying amount of fat in milk is not a problem – all the milk is good! It enables babies to quench their thirst at the start of a feed and finish with a creamy “dessert”, if they want to.
The balance of fat in milk can be a problem for a small number of babies, if:
- The baby is taken off the breast before they have had as much milk as they wanted; or
- There is an overwhelming amount of milk. In this case, the baby may be growing very fast (their growth curve crosses centiles upwards on the growth chart) and may struggle with the speed of milk flow, coming off the breast gagging, spluttering and upset. You can find practical tips to help your baby manage fast milk flow here.
In either of these two situations, the baby may not get enough fat to slow down the transit of milk through their gut. Milk may rush through the gut faster than the baby can digest the milk sugar (lactose). The sugar ferments in the gut, producing green, frothy, explosive poo, flatulence (farting) and severe discomfort.
A baby who does yellow poo and is comfortable does not have any problem with the balance of fat in their diet. A baby who is growing more slowly than expected needs more milk overall, not just more fat. These babies should be seen by a doctor to rule out an underlying health problem.
You can read more about fat levels in milk here.
How much milk?
In the first 24 hours after birth, volumes of colostrum are small, but enough for your baby. The average amount per feed is about 7ml (1 ½ teaspoons). This is because full-term babies are not hungry – they are born with food stores in their body. They don’t need fluid – they shed extra fluid in the first few days (this is why most babies lose a little weight). Colostrum is primarily immune protection, rather than food. It coats the inside of the baby’s gut to keep pathogens out, stimulates the baby’s immune system, and provides the baby with a powerful, tailor-made dose of growth factors, hormones, live immune cells and other components that no manufactured milk can begin to match.
The small quantity and thick texture of colostrum give the baby a chance to practice feeding before they have to manage larger volumes. The amount of colostrum increases quickly, more or less doubling every day in the first few days. If you need to express on the first day after birth, you might use a syringe to catch drops. A syringe quickly becomes too small for the increasing volumes. By the 5th day after birth a baby might be taking 60ml (2oz) or more per feed.
If you are expressing your milk, for example because your baby was born early, it can help to know how much to aim for:
- 500ml in 24 hours by the end of the first week after birth
- 750ml in 24 hours by the end of the second or third week after birth
Your baby might not need this much milk yet, but aiming for a full supply now means you will have enough to satisfy them for the rest of their breastfeeding time.
Milk production remains stable, within a range of about 600ml – 1200ml per 24 hours, from about one month after birth to six months. After the baby starts eating complementary foods, milk production starts to decrease, as milk is gradually replaced by other foods in the baby’s diet. If you are making as much milk as your baby needs at one month, you are likely to keep on doing so, as long as your baby keeps on removing enough milk and you don’t get pregnant or use one of a small number of medications that can affect milk production. Birth control methods that contain progesterone may reduce milk production in some women.4
How milk changes
If you are expressing your milk, you will be able to see the change from sticky, transparent, yellow or orange colostrum to thinner, white or blue-ish “transitional milk” by about the fourth day after birth. The composition of your milk is changing to adapt to your baby’s need for more energy. Your milk changes from day to day for as long as you breastfeed or express, responding to your baby’s stage of development, any illnesses you or your baby are in contact with, and even the time of day or night it was made.5 The milk of mothers who give birth prematurely is initially different from the milk of mothers who give birth at full term, to meet the extra needs of their babies.
Getting back on track after a difficult start
Milk production peaks by about a month after birth, with most of the increase happening in the first two weeks. Many mothers find it becomes more difficult – in some cases impossible – to increase the amount of milk they are making, after the early weeks. This is why it is important to get good feeding support early, if there are any signs that there might be a problem with your baby getting enough milk, for example, if your baby:
- Does not poo every day (in the first 4-6 weeks)
- Has pink crystals (urates) in their nappy after the third day
- Is not doing yellow poo by the end of the fourth day
- Loses more than 7% of their birth weight by the fifth day
- Loses weight after the fifth day
- Does not regain their birth weight by 10-14 days
An LLL Leader or infant feeding specialist can help you work out whether there is likely to be a problem with milk production or whether (more commonly) your baby is not yet feeding effectively. If not enough milk is being removed, the risk is that your milk production will not increase to the level your baby needs. Expressing your milk gives you time to work on any feeding issues.
If the problem is with milk production, your breastfeeding supporter can help you make a plan to keep your baby safely fed while you work to maximise your milk supply. You will need to work closely with your baby’s healthcare providers to monitor their growth and wellbeing.
Lactation beyond the early months
Parents are sometimes told that their milk has no value to their baby after 6 months, or 12 months. This is not the case. Milk is the baby’s main source of protein and calories until about a year of age, and continues to contribute to the child’s health and nutrition through the second year and beyond.
Your milk adapts to meet your baby’s needs as they grow. For example:
- From about six months, the digestive enzyme amylase starts to be present in milk, helping your baby digest starchy foods.
- From about six months, levels of the antibacterial enzyme lysozyme increase in milk, protecting your baby as they put foods and other objects in their mouth.
- As the total amount of milk begins to decrease gradually, from about six months, levels of key immune factors such as immunoglobulins increase, so that the child receives about the same amount per day, even though they take less milk.
- Levels of fat, protein and energy in milk are higher in the second year than in the first year of lactation.6 7
Lactation ends – involution
Milk will continue to be made in the breast for as long as milk is removed from the breast. In the early days of lactation, milk supply is relatively fragile – the mother’s body quickly shuts down production if milk removal stops. In later lactation, milk production is much more robust. Mothers returning to work after six months, for example, can be confident that their milk supply will withstand variations in their schedule from day to day and week to week. In later lactation it is possible to breastfeed part-time, even if you work shifts or need to travel away overnight. Many breastfeeding toddlers and older children spend time away overnight with a non-resident parent, grandparents, etc. and continue breastfeeding when they are with their mother.
It takes at least 40 days for the breast to reach complete “involution” (a non-lactating state) after the end of breastfeeding or milk expression. Some mothers find that they leak or can express drops of milk months or even years after their last feed. If the amount of milk is large, or you start making milk again after a gap even though you are not pregnant, check with your doctor. Spontaneous milk secretion (galactorrhoea) can be a side effect of some medications, or a sign of hormonal dysfunction.
When children are able to wean from the breast at their own pace, weaning often takes place over a period of months and years. The most common time for children to choose to stop breastfeeding is between their second and third birthdays.8 Milk production reduces gradually and, by the time the child has their final feed, may have dwindled to almost nothing. Some of the immune components of milk become more concentrated as milk volumes decrease, so the child continues to benefit to the last drop of breastmilk.
Written by Jayne Joyce, LLL Oxfordshire and Karla Napier, LLL Edinburgh – February 2021