Insufficient milk supply is the most common reason women give for needing to supplement with formula or to wean their baby from the breast

There is great variability of daily milk volumes generated by lactating women who are successfully and exclusively breastfeeding their babies in the first six months of life (600 mls to more than twice that in a 24-hour period). For this reason, 'low supply' is best conceptualised as a mismatch between a woman's breastmilk production and her infant's caloric needs.

The term physiological needs, commonly used in breastfeeding education in the phrase "unable to meet her infant's physiological needs", doesn't make sense, to my mind, as an infant's physiological needs are complex and include many more considerations than the infant's caloric needs, such as the need for temperature regulation or airway protection. The infant's caloric needs are the fundamental measure used to determine whether or not she is growing adequately and her mother has a sufficient milk supply.

Many women who wish to breastfeed report concerns about insufficient milk supply. It's been estimated that up to two in five women don't make enough milk for their babies. For example, Shen et al 2021 reported that up to 74% of women reported not having enough milk for their baby in the immediate postpartum.

What are the causes of low supply?

One way of thinking about milk production and the factors which impact to result in milk production which doesn't meet the infant's needs is to note that we require

1. Sufficient mammary glandular tissue, potentially interfered with by

   • Mammary gland hypoplasia

   • Breast surgery

2. Normal hormonal levels, potentially interfered with by

   • Postpartum haemorrhage

   • Retained placenta

   • Chronic medical conditions (hypothyroidism, anaemia, PCOS, diabetes, obesity, medications, cigarettes and alcohol)

3. Regular effective milk removal, potentially interfered with by

   • Delivery complications

   • Infant sedation

   • Poor fit and hold

   • Infant formula

   • Infant medical problems.

From now on in this article, though, we'll consider low supply through the lens of primary and secondary insufficient milk supply, and perceived milk supply.

Primary insufficient milk supply

Primary insufficient milk supply occurs in 10-15% of breastfeeding women, and may result from a range of conditions, including

• Previous breast surgery, which has severed the lactiferous ducts

• Metabolic dysfunction such as diabetes, obesity, polycystic ovarian syndrome (PCOS), which may interfere with hormones involved with breast development and milk synthesis

• Mammary hypoplasia.

Pregnancy complications are associated with increased risk of low supply

• Gestational diabetes (x 7 increase)

• Gestational hypertension (x 8.8 increase)

• Low birth weight baby (x 12 increase). (Wlodek, Perrella, Geddes et al unpublished)

However, women with breast hypoplasia may be able to produce enough milk to exclusively meet their infant's caloric needs, so breast hypoplasia needs to be distinguished from Insufficient Glandular Tissue, discussed here.

It is not usually possible to know just how well we can retrieve or build milk supply, until we’ve put in place the strategies which optimise milk production. Unfortunately, women often don’t receive good advice about stabilising fit and hold and frequent flexible breastfeeds, which needs to be the focus even when they have a diagnosis which is known to increase the risk of low supply.

Secondary insufficient milk supply

Secondary insufficient milk supply results from

1. Suboptimal breastfeeding management. I propose that there are currently high levels of secondary insufficient milk supply because of health system blind spots concerning clinical breastfeeding and lactation support, in particular concerning fit and hold, and the importance of frequent and flexible feeds.

2. Commencement of hormonal contraception

   • The weight of evidence suggests that progestin-only contraceptives (oral, injection, implant or intrauterine device) don't impact breastfeeding outcomes.

   • Combined hormonal contraceptives are reported in some studies to decrease breastfeeding duration and increase supplemental feeding, whereas others have found no difference. Current recommendation is not to use combined hormonal contraception until after six weeks postpartum.

3. Infant medical conditions which impair infant milk transfer. These include

   • Cleft palate

   • Down syndome

   • Neurological disturbances

   • Hypothyroidism

   • Ankyloglossia (overdiagnosed).

Perceived insufficient milk supply

Perceived insufficient milk supply results from maternal or parental or health professional perceptions of infant behaviours and observations and feelings about the breast which are real to those concerned, but which don't correlate with scientific or objective indicators of insufficient milk supply.

I propose that there are currently high levels of perceived insufficient milk supply because of health system blind spots concerning clinical breastfeeding and lactation support, in particular misinterpretation of infant behaviours in the context of suboptimal fit and hold, and feed spacing.

For example, early introduction of formula in hospital has been estimated at 28% in the UK, but the authors of that study found many of the factors implicated in early supplementation to be modifiable, so that the women introducing formula were experiencing either secondary or perceived insufficient milk supply.

Breast inflammation, delayed onset of lactation, and decreased milk supply

While both conditions of breast inflammation or delayed secretory activation are characterised by an elevated human milk sodium concentration and sodium:potassium ratio, to date there are no clinical tools available to track these complications of lactation.

Heron et al validated the reliability of handheld devices for determining sodium and potassium levels in human milk. The authors suggested these may offer a promising point of care tool for monitoring secretory activation, the onset of mastitis, and evaluation of treatment. However, as a clinician I don't see a rason to believe that these tools will perform better than thorough clinical history-taking and assessment.

Mastitis, a commonly recognized cause of primary lactation insufficiency, can result in gland damage and/or activation of unplanned involution, both of which would lead to removal of milk producing cells, reducing milk production.

Delayed secretory activation or impaired secretory activation due to medical conditions can sometimes cause low supply (but is often blamed when in fact it is the other more common causes that haven’t been addressed)

Is liver pathology a cause of primary insufficient milk supply?

It's hypothesised that the liver is an essential player in lactation because during lactation the liver

• Has increased glucose production

• Has increased metaboic processing of lipids, and

• Shuttles these and other vital milk components to the mammary gland.

In lactation, a 'mammary gland-liver' functional unit activates, to meet the metabolic demands of milk production. The liver has been found to change composition and increase in size during pregnancy and lactation in rodents, and decrease in size at weaning. It's unknown if liver pathologies impede successful lactation.

However, human lactation duration of six months or longer has been associated with reduced incidence of

• Non-alohoic fatty liver disease

• Breast cancer.

Selected references

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

Heron E, Lai CT, McKenna LJ, McArdle AM, Geddes DT. Imediate point-of-care testing of breastmilk sodium and potassium concentrations in women with mastitis. Proceedings. 2023;93(1):https://doi.org/10.3390/proceedings2023093001.

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.

Jin X, Perrella SL, Lai CT, Taylor N, Geddes DT. Causes of low milk supply: the roles of estrogens, progesterone, and related external factors. Advances in Nutrition. 2024;15(1):100129.