As lactation professionals, we know that milk production is influenced by many factors—hormonal balance, birth practices, infant behavior, maternal motivation, frequency of feeding, and more. Yet even when all these align, some parents still struggle with producing enough milk. One often overlooked reason is breast hypoplasia—sometimes referred to as insufficient glandular tissue (IGT). This condition may result in primary low milk supply, meaning a person is physiologically unable to make enough milk despite frequent and effective milk removal.

Breast hypoplasia is more than an anatomical variant; it is a medical reality that can cause significant physical, emotional, and relational stress for families. Recognizing the signs, understanding the etiology, and providing evidence-based support are crucial responsibilities for lactation consultants and birth professionals.

What Is Breast Hypoplasia?

Breast hypoplasia refers to underdevelopment of the mammary glandular tissue, which may result in insufficient capacity to produce a full milk supply. It is important to differentiate this condition from secondary causes of low milk supply (e.g., infrequent milk removal or latch issues) and from perceived low supply. In cases of true hypoplasia, the structural development of the breast—specifically the milk-making lobules and ducts—is inadequate (Kam et al., 2021a; Farah et al., 2021).

Clinically, breast hypoplasia may be suspected when lactogenesis II is delayed or does not occur, even with early and frequent stimulation. It may also present when the infant fails to gain weight despite good latch and frequent feedings, and other causes have been ruled out (Spatz & Miller, 2021).

How the Breast Develops: Physiology Overview

To understand hypoplasia, it helps to review normal breast development. Mammary development occurs in stages:

1. Embryogenesis – The basic mammary structures form.

2. Puberty – Hormonal influence (estrogen, progesterone, growth hormone) leads to ductal and lobular growth.

3. Pregnancy – Prolactin, estrogen, and progesterone drive full glandular development, preparing the breast for milk synthesis.

Lactation proceeds through:

• Lactogenesis I – Secretory differentiation begins around 16–20 weeks of pregnancy.

• Lactogenesis II – Copious milk production begins postpartum, typically within 72 hours.

• Lactogenesis III (Galactopoiesis) – Milk supply is maintained by autocrine control, meaning frequent and effective milk removal (Farah et al., 2021).

Disruptions at any developmental stage—especially in puberty and pregnancy—can result in insufficient glandular tissue and low milk supply.

What Causes Breast Hypoplasia?

Congenital or Genetic Causes

Hypoplasia may be idiopathic (no known cause) or part of a syndrome. Some examples:

• Poland Syndrome: Underdevelopment of chest wall and pectoral muscle

• Jeune Syndrome: Skeletal dysplasia affecting thoracic development

• Pectus Excavatum: Chest wall deformity that can co-occur with mammary underdevelopment (Winocour & Lemaine, 2013)

Endocrine and Hormonal Factors

Hormonal conditions play a major role:

• Polycystic Ovary Syndrome (PCOS): Women with PCOS are more likely to have impaired mammogenesis and delayed lactogenesis II (Vanky et al., 2008)

• Obesity and Insulin Resistance: These can impair prolactin receptor activity and affect glandular tissue development (Kam et al., 2021a)

• Thyroid Dysfunction: Hypothyroidism can delay lactogenesis and reduce supply (Farah et al., 2021)

Environmental and Acquired Influences

Emerging research suggests:

• Exposure to endocrine-disrupting chemicals during puberty or in utero may impair breast development (Kam et al., 2021c)

• Breast surgery, trauma, or radiation may damage developing tissue or remove lobules needed for milk production (Winocour & Lemaine, 2013)

How Common Is It?

The prevalence of true breast hypoplasia is unknown due to lack of population-based data. It is often underdiagnosed or misattributed to behavioral or mechanical issues. Kam et al. (2024) note that among 487 women in low milk supply Facebook groups, 68% reported having at least one marker suggestive of hypoplasia. This highlights the need for greater awareness and better diagnostic criteria.

Recognizing the Signs: Physical and Clinical Indicators

Kam et al. (2024) and Huggins et al. (2000) outline several commonly observed features of breast hypoplasia:

• Tubular or tuberous breast shape

• Marked asymmetry (≥ 2 cup size difference)

• Wide intramammary space (≥ 3.8 cm or 1.5 inches)

• Lack of breast growth during pregnancy

• Minimal or absent breast fullness postpartum

• Stretch marks on breasts without enlargement

While these features can suggest hypoplasia, they are not diagnostic on their own. The presence of one or more features, combined with low milk production despite frequent removal, may warrant further evaluation.

Kam et al. (2021b) found that measuring intermammary width (IMW) had excellent interrater reliability and may be a useful objective tool. However, categorizing breast “types” by appearance had only moderate reliability, reinforcing the importance of a holistic, clinical approach.

Assessment and Diagnosis: What Can We Do?

Prenatal anticipatory guidance and postpartum assessment are critical. Professionals should ask:

• Did the breasts change during pregnancy or puberty?

• Was there noticeable engorgement after birth?

• Is the baby feeding well but not gaining weight?

• Has pumping output been consistently low?

Tools to consider:

• IMW measurement for spacing

• Weighted feeds to assess transfer

• Pumping logs to track output

• Endocrine history and screening, especially if PCOS or thyroid issues are suspected

Always rule out modifiable causes of secondary low supply before assuming primary insufficiency.

Clinical Management Strategies

When breast hypoplasia is suspected, the clinical approach should prioritize:

Maximizing Existing Milk Supply

• Early and frequent milk removal—at least 8–10 times per day

• Use of hospital-grade pumps with Initiation Technology

• Galactagogues (e.g., domperidone, metoclopramide) when clinically indicated (Duran & Spatz, 2011)

Supporting the Infant’s Nutritional Needs

• Supplemental nursing systems (SNS) to offer formula or donor milk at the breast

• Careful monitoring of weight, hydration, and development

Emotional and Psychological Support

• Validate the parent’s efforts and grief

• Reinforce that any amount of human milk is valuable

• Offer connection to support groups and informed providers

Spatz and Miller (2021) stress that anticipatory guidance and a nonjudgmental approach are vital. They describe a mother who did not receive prenatal breast assessment or counseling and struggled with guilt and confusion postpartum.

Research Gaps and Future Directions

Despite decades of case reports, there is still no universally accepted definition or diagnostic criteria for breast hypoplasia. Key research priorities include:

• Establishing population-level prevalence estimates

• Developing validated diagnostic tools beyond appearance

• Studying endocrine and environmental contributors

• Evaluating intervention efficacy in cases of primary low supply

Lactation professionals can play a vital role in advancing awareness, supporting affected families, and contributing to clinical data collection.

Conclusion

Breast hypoplasia is a legitimate, underrecognized cause of low milk supply. While it is relatively rare, it carries significant consequences for affected dyads. Lactation consultants and healthcare providers must be prepared to recognize the signs, understand the contributing factors, and guide families through evidence-based, compassionate care.

Let’s be clear: supporting breastfeeding means supporting all breastfeeding journeys—including those where full milk supply is not possible. By equipping ourselves with knowledge and empathy, we can help families find clarity, confidence, and connection—no matter how much milk is made.

References

Arbour, M. W., & Kessler, J. L. (2013). Mammary hypoplasia: Not every breast can produce sufficient milk. Journal of Midwifery & Women’s Health, 58(4), 457–461. https://doi.org/10.1111/jmwh.12001

Breastfeeding Review. (2015). PCOS, breast hypoplasia and low milk supply: A case study. Breastfeeding Review, 23(3), 29–32.

Duran, A. M., & Spatz, D. L. (2011). A mother with glandular hypoplasia and a late preterm infant. Advances in Neonatal Care, 11(3), 200–204.

Farah, E., Barger, M. K., Klima, C., Rossman, B., & Hershberger, P. (2021). Impaired lactation: Review of delayed lactogenesis and insufficient lactation. Journal of Midwifery & Women’s Health, 66(5), 631–640. https://doi.org/10.1111/jmwh.13274

Huggins, K. E., Petok, E., & Mireles, O. (2000). Markers of breast hypoplasia and insufficient milk supply. Contemporary OB/GYN, 45(9), 43–48.

Kam, R. L., Amir, L. H., & Cullinane, M. (2021a). Is there an association between breast hypoplasia and breastfeeding outcomes? A systematic review. Breastfeeding Medicine, 16(8), 594–602. https://doi.org/10.1089/bfm.2021.0032

Kam, R. L., Cullinane, M., Vicendese, D., & Amir, L. H. (2021b). Reliability of markers for breast hypoplasia in the early postpartum period. Journal of Human Lactation, 37(2), 242–250. https://doi.org/10.1177/0890334421991071

Kam, R. L., Amir, L. H., & Cullinane, M. (2021c). Research challenges and considerations in investigating rare exposures using breast hypoplasia as an example. Journal of Human Lactation, 37(4), 633–638. https://doi.org/10.1177/08903344211037620

Kam, R. L., Amir, L. H., Cullinane, M., Ingram, J., Li, X., & Nommsen-Rivers, L. A. (2024). Breast hypoplasia markers among women who report insufficient milk production: A retrospective online survey. PLOS ONE, 19(2), e0299642. https://doi.org/10.1371/journal.pone.0299642

Sandoval-Pinto, E., García-Gutiérrez, M., Acosta-Real, S., Sierra-Díaz, E., & Cremades, R. (2023). Characterization of three cases of primary hypogalactia in Jalisco, Mexico. Journal of Human Lactation, 40(1), 143–149. https://doi.org/10.1177/08903344231201613

Spatz, D. L., & Miller, J. (2021). When your breasts might not work: Anticipatory guidance for health-care professionals. The Journal of Perinatal Education, 30(1), 13–18. https://doi.org/10.1891/J-PE-D-20-00014

Vanky, E., Isaksen, H., Moen, M. H., & Carlsen, S. M. (2008). Breastfeeding in polycystic ovary syndrome. Acta Obstetricia et Gynecologica Scandinavica, 87(5), 531–535. https://doi.org/10.1080/00016340802021941

Winocour, S., & Lemaine, V. (2013). Hypoplastic breast anomalies in the female adolescent breast. Seminars in Plastic Surgery, 27(1), 42–48. https://doi.org/10.1055/s-0033-1343996