Low milk supply is a common concern among breastfeeding parents and one of the leading reasons for early weaning. For lactation professionals, understanding the nuances between primary and secondary low milk supply is essential for providing effective, evidence-based support. This first post will clarify the differences, outline prevalence data, and explore causes and diagnostic red flags.

What is Low Milk Supply?

Low milk supply refers to a situation where a lactating parent does not produce enough milk to meet their baby’s nutritional needs. However, it’s crucial to distinguish between:

Primary low milk supply – This is an intrinsic issue within the parent’s physiology or anatomy. It means that, even with optimal breastfeeding practices, the milk production capacity is insufficient (Whelan et al., 2025).

Secondary low milk supply – This is a situational or modifiable problem where external factors interfere with effective milk production, despite the parent’s natural ability to make enough milk (Riddle & Nommsen-Rivers, 2016).

Perceived low milk supply (PIM) – Often, parents may believe they have low supply due to normal newborn behaviors or growth patterns. Unlike true low supply, PIM typically resolves with education and reassurance (Neifert et al., 1985).

Prevalence and Epidemiology

Primary low milk supply is relatively rare, affecting an estimated 1–5% of breastfeeding parents (Robert et al., 2014; Whelan et al., 2025). Most cases of low milk supply are actually secondary, stemming from fixable issues like poor latch or feeding management (Baker et al., 2021).

Interestingly, perceived low milk supply is much more common. Studies report that 30–50% of mothers cite “not enough milk” as a reason for early weaning—though true physiological low supply only occurs in a fraction of these cases (Verd et al., 2022).

Causes of Primary Low Milk Supply

Insufficient Glandular Tissue (IGT)

IGT occurs when the breast does not develop enough milk-making tissue during puberty or pregnancy. Breasts may appear unusually shaped (tubular, widely spaced) and may not undergo normal enlargement during pregnancy (Neifert et al., 1985; Whelan et al., 2025).

Hormonal and Endocrine Disorders

Successful lactation depends on hormonal balance—prolactin, oxytocin, insulin, and thyroid hormones. Disruptions can impair milk production:

• Polycystic Ovary Syndrome (PCOS):

  Linked to insulin resistance and high androgens, both of which can interfere with lactation (Verd et al., 2022).

• Thyroid Dysfunction

  : Especially hypothyroidism, which can reduce milk synthesis (Baker et al., 2021).

• Pituitary Issues

  : Sheehan’s syndrome (from postpartum hemorrhage) damages the pituitary, resulting in low prolactin (Riddle & Nommsen-Rivers, 2016).

Metabolic Health Challenges

Conditions like obesity, insulin resistance, and diabetes are increasingly recognized contributors to low milk supply. Insulin plays a role in lactation, and impaired insulin signaling can hinder milk production (Verd et al., 2022).

Breast Surgery or Trauma

Procedures such as breast reductions, augmentations, or injuries can damage milk ducts and nerves, limiting milk production (Nommsen-Rivers et al., 2019).

Causes of Secondary Low Milk Supply

Secondary low milk supply develops when milk production is suppressed by external factors. Common causes include:

Inadequate Breast Emptying: The most common cause. Infrequent or incomplete milk removal signals the body to reduce milk production (Riddle & Nommsen-Rivers, 2016).

Poor Latch or Ineffective Sucking: If the baby can’t effectively remove milk due to tongue-tie, prematurity, or other oral-motor issues, milk supply can drop (Whelan et al., 2025).

Supplementation with Formula: Formula given unnecessarily early on can reduce demand on the breast, leading to decreased milk supply (Baker et al., 2021).

Maternal Medications or Health Conditions: Certain medications (e.g., decongestants, estrogen-containing contraceptives) and maternal smoking can inhibit milk production (Verd et al., 2022).

Separation from the Baby: Hospitalizations or maternal illness can limit breastfeeding, reducing supply if not balanced with effective pumping (Riddle & Nommsen-Rivers, 2016).

Diagnostic Considerations: Identifying Low Milk Supply

Accurate diagnosis requires a holistic assessment of both the parent and baby. Key elements include:

Infant Growth and Weight Patterns

• Weight loss >10% of birth weight

• Lack of weight regain by day 10–14

• Slowed weight gain below 20–30 grams/day in early weeks (Verd et al., 2022)

Infant Output and Behavior

• Fewer than 6–8 wet diapers per day after the first week

• Infrequent stooling or hard stools

• Excessive sleepiness or frustration at the breast

Maternal History and Breast Changes

• Little to no breast growth in pregnancy

• Lack of engorgement by day 5 postpartum

• History of endocrine disorders or breast surgery

Weighted Feeds and Latch Assessments

• Pre- and post-feed weights to confirm milk transfer

• Direct observation of latch and feeding dynamics by an IBCLC

Red Flags for Primary Low Supply

• No breast changes during pregnancy

• Significant endocrine/metabolic history (PCOS, thyroid disease, diabetes)

• Persistent low output despite optimal breastfeeding management

Emotional and Psychosocial Impact

For parents, low milk supply—especially primary—can be devastating. Research highlights feelings of grief, guilt, and even trauma when a parent’s milk supply doesn’t meet their baby’s needs (Whelan et al., 2024). Many report feeling misunderstood or dismissed by healthcare professionals (Whelan et al., 2025).

Empathetic, evidence-based lactation care is crucial. Studies show that parents value not only skilled clinical help but also emotional validation and understanding from lactation professionals (Whelan et al., 2025). By creating a safe space for grieving and exploring options, professionals can support parents’ mental health while optimizing feeding.

Conclusion & What’s Next

Low milk supply is multifactorial, with primary and secondary causes often requiring very different approaches. Understanding the distinctions, epidemiology, and diagnostic clues is essential for lactation professionals at all levels. In Part 2, I’ll cover evidence-based treatment strategies, including:

• Non-pharmacological support (latch optimization, pumping, feeding plans)

• Pharmacological treatments and herbal options

• Emerging research and individualized care approaches

Stay tuned!

References

Baker, H., Shere, H., & colleagues. (2021). Chronic lactation insufficiency is a public health issue: Commentary on “We need patient-centered research in breastfeeding medicine.” Breastfeeding Medicine, 16(6), 349–350.

Neifert, M. R., Seacat, J. M., & Jobe, W. E. (1985). Lactation failure due to insufficient glandular development of the breast. Pediatrics, 76(5), 823–828.

Nommsen-Rivers, L. A., et al. (2019). Feasibility and acceptability of metformin to augment low milk supply: A pilot randomized controlled trial. Journal of Human Lactation, 35(2), 371–381.

Riddle, S. W., & Nommsen-Rivers, L. A. (2016). A case-control study of diabetes during pregnancy and low milk supply. Breastfeeding Medicine, 11(1), 14–19.

Robert, E., Doumont, A., & Piette, D. (2014). The reasons for early weaning, perceived insufficient breast milk, and maternal dissatisfaction: Comparative studies in two Belgian regions. BioMed Research International, 2014, 678564.

Verd, S., Perapoch, J., & Nommsen-Rivers, L. A. (2022). Measures of maternal metabolic health as predictors of severely low milk production. Breastfeeding Medicine, 17(7), 566–576.

Whelan, C., O’Brien, D., & Hyde, A. (2024). Mother’s emotional experiences of breastfeeding with primary low milk supply in the first four months postpartum: An interpretative phenomenological analysis. Breastfeeding Medicine, 19(3), 197–207.

Whelan, C., O’Brien, D., & Hyde, A. (2025). Breastfeeding with primary low milk supply: A phenomenological exploration of mothers’ lived experiences of postnatal breastfeeding support. International Breastfeeding Journal, 20(7). https://doi.org/10.1186/s13006-025-00699-4