Why do some women's breasts not make enough milk to meet their baby's caloric needs?

"She looked from Leonie to Therese and she smiled. "Of course I fed you both, silly. I had plenty of milk didn’t I …." Rose in her chair by the fire, feet up, blouse undone, a lapful of babies, a shout of joy, the smell of milk, there, my dears, there." Michele Roberts, Daughters of the House p 169

"Flourish ….. To grow luxuriantly, or thrive in growth." The Macquarie Dictionary p 687

To make milk you need to take milk from your breasts

The most important thing to remember is that increasing the amount of breast milk you remove from your breast increases the amount of breast milk you make.

However, no-one knows exactly how why this happens. There are various models used (which might be wrongly told to you as if they are fact). In the Possums programs, I work from the NDC two-part mechanobiological model of breastmilk production. The research findings from which I've developed this model are in the modules for health professionals. Here's what I think, drawing on the latest research.

1. When the baby removes milk more often, there is less backpressure building up in the milk glands. High backpressure in a gland decreases the lactocytes' milk secretion. This happens because of mechanical pressure effects on the lactocytes (the milk-making cells) and also on the junctions between the lactocyte. You can find out more about this here.

2. Your milk letdowns also cause a different kind of mechanical pressure, as your milk glands scrunch or squeeze up to press out the milk. At the same time, your letdown makes your milk ducts dilate, opening up to carry that milk down the ducts and out as easily as possible. As a result of your letdown, waves of pressure changes sweep throughout your breasts' connective tissues. The more frequently you have these pressure changes, the more the stem cells in your breasts' alveoli and ducts and connective tissues are stimulated to grow into new milk-making cells.

The worry that baby is not receiving enough milk is the main reason women give for starting formula

It's very upsetting to find that you're not making enough milk to meet your baby's weight gain needs. Here I hope to give you a handle on what might be going on, as you think through - hopefully with the help of your breastfeeding support professional - how you might change this upsetting situation, even if you've needed to start supplementing with formula or donated milk.

You're definitely not alone. The most common reason women give all around the world for needing to stop breastfeeding is that they don't have enough milk. It's not clear how many breastfeeding women have low supply, since estimates vary from 10% to 33%. One study even found that two-thirds of women didn't make enough milk in the first weeks after their baby's birth. Unfortunately, we often have milk production problems because of our health systems' blind spots about breastfeeding.

You have what we might call a 'full' milk supply if you're able to produce enough milk to meet your baby's growth needs in the first six months of life without supplementing with formula or donor milk. But the amount of milk produced daily by women with 'full' milk supply varies enormously. You can find out how much milk breasts make here.

You might be worrying that you don't have enough milk because your baby doesn't seem satisfied. But a dialled up baby is not necessarily a hungry baby. If you have a baby who is dialled up as a pattern over time, one of the first things to explore is whether or not your baby is gaining weight well. If he is following his percentile line nicely as a pattern over time on the World Health Organisation growth charts, then you might start to think about the other things that can make your baby appear dialled up and hungry (such as your baby's sensory motor needs), when that's not the case.

• You can find out how to tell if your baby is getting enough milk here.

• You can find out what are not signs of low supply here.

• You can find out about your baby's sensory motor needs here.

• You can find out why you don't need to burp your baby here.

The three main causes of low milk supply

Usually many things interact together to effect your milk supply, and some women have much more buffer built into their supply settings than others, for genetic reasons. This is one reason why you might have had exactly the same breastfeeding experiences as your friend, but your friend is making plenty of milk for her baby down the track, and you aren't.

It's usually not because of innate pathologies in your baby's capacity to suck, though you'll often hear this said.

1. Your milk production settings might be affected both in the short- and long-term if there's not enough vacuum stimulation of your nipple and breast during the sensitive first days after your baby's birth

A very common cause of low supply is not enough milk removal in the first hours and days of your baby's life. (It's not that there is much colostrum available to be removed. It's the stimulation and removal of what is there that counts.)

The first day or first few days after your baby is born set the trajectory of your breasts capacity to produce milk.

For example, a woman’s supply by the end of the first fortnight predicts her supply at the end of six weeks. You can find out about this here.

Not enough milk removal at the very beginning means that your milk supply might peak at a lower setting than it otherwise would, and this might persist for the rest of your breastfeeding relationship with your baby.

Lots of women manage to heroically repair their supply and go on to exclusively and happily breastfeed their baby despite a very difficult start with breastfeeding, including lots of formula supplementation. For others, no matter how hard they try, exclusive breastfeeding never becomes possible. All we can do is give it our best, accepting that much in life - and in breastfeeding - is outside our control.

2. Too much backpressure building up in your milk glands is another very common cause of low milk supply

Not making enough milk to meet your baby's needs without supplementation very commonly results from too much backpressure in your milk glands, itself caused by not enough milk removal, resulting in decreased or downregulated milk production. You can find out about the mechanical effects of backpressure in your milk glands here.

Too much backpressure results from

• Baby's positional instability at the breast, which causes breast tissue drag and inadequate milk removal. You can find out about this here.

• Not being able to resolve nipple pain and damage, which makes it very difficult to breastfeed often enough. You can find out about this here.

• Having severe or repeated breast inflammation. You can find out about this here.

• Advise to space out breastfeeds. You can find out about this here.

Unfortunately, although formula use can be essential for your baby's safety (given the difficulty many families face accessing donor milk), using formula can also quickly decrease your breast milk supply. This is because your baby has less of an appetite drive to take milk from your breasts.

• You can find out about formula use here.

• You can find out about pumping breast milk here.

3. Some women are never able to breastfeed their baby without some supplementation due to an underlying medical condition or genetic factors

There is a difference between

1. A temporary low supply which isn’t enough to meet your baby’s needs for growth but which can be recovered through various strategies

2. A low supply resulting from early breastfeeding problems or not enough milk removal in the early days, but your breast milk supply settings are not able to recover. Some women's capacity to make milk seems to be more resilient in the face of setbacks than others, for genetic reasons.

3. A low supply due to medical or metabolic conditions which can’t be fixed, only managed as best we can.

It is mostly not possible to know just how much any medical condition is going to effect your supply, until we’ve put in place all the strategies which optimise your milk production. Unfortunately, women often don’t receive good advice about the basics of fit and hold and frequent flexible breastfeeds.

Yet good fit and hold and frequent flexible breastfeeds are essential for making the most milk you possibly can, even when you are managing a medical or metabolic or anatomic diagnosis which is known to affect milk supply.

You can find out about your supply and

• Type 1 or type 2 diabetes here

• Polycystic ovary syndrome here

• Iron supplementation here

• Insufficient glandular tissue here

• Being a larger-bodied woman here.

Please note: Possums Breastfeeding & Lactation does not yet address prematurely born babies and breastfeeding (under development).

Selected references

Jin X, Lai CT, Perrella SL. Maternal breast growth and body mass index are associated with low milk production in women. Nutrients. 2024;16(2854):https://doi.org/10.3390/nu16172854.

Geddes DT, Prosser SA, Gridneva Z, Perrella SL. Risk factors for low milk production. Proceedings. 2023;93(17):https://doi.org/10.3390/ proceedings2023093017.