Does Breast Size Matter?

Does Breast Size Matter
Explaining Breast Storage Capacity and Insufficient Glandular Tissue

Breasts come in all shapes and sizes. Regardless of size, with the right information and support, most nursing parents are able to produce a full milk supply. So, does size matter when it comes to milk production?

Breasts consist of:

  • Fatty tissue: provides protection to the other tissues and structures within the breast
  • Glandular tissue (milk ducts): makes and and transports milk to the nipple
  • Connective tissue (muscles and ligaments): supports the structure of the breast
  • Nerves: provide the sensory response that is needed for milk ejection or letdown
  • Blood: brings nutrients to the breast to create milk
  • Lymph: removes waste products from the breasts

The size of any breast is determined mostly by the amount of fatty tissue in the breast. Fatty tissue is not involved in the production of breastmilk.

During pregnancy and lactation the amount and density of glandular tissue increases. On average, there is about twice as much glandular tissue as fatty tissue in the breast. Approximately 70% of the glandular tissue is found within a 30 mm (one inch) radius of the nipple. Thus, a baby with a good deep latch is reaching the majority of the glandular tissue when he compresses his jaws during a feeding.

Breast size is not a good indicator of future milk production. A better indicator is an increase in breast size during pregnancy. Needing bigger bras as the pregnancy moves along is a clear sign that glandular tissue is developing. If you notice minimal or no change in the size of your breasts during your pregnancy, contact an International Board Certified Lactation Consultant (IBCLC) before your baby arrives. This might indicate minimal growth of the milk glands. To monitor issues with milk production, it will be important to check your baby’s weight gain in the early weeks.

Most pairs of breasts are not identical in size or shape. For most women these slight differences aren’t noticeable prior to pregnancy. You may find that your breasts become obviously different in size and shape when you are pregnant and lactating. There may be more glandular development on one side than the other. This may be due to a past injury to the breast or for unknown reasons.

The difference in size and/or shape of a breast may or may not influence milk production, milk storage capacity or baby’s preference for one side over the other.

One of the phrases that is used a lot when discussing milk supply and nursing frequency is "breast storage capacity". Breast storage capacity varies from person to person. It is not related to breast size because storage capacity is created by glandular tissue not fatty tissue. However, it may be one factor that explains the differences in feeding frequency between one breastfeeding pair and another. Breast storage capacity is the most milk available to your baby when the breast is at its fullest. When measured in studies, the storage capacity ranged from 2.6 oz (74 g) to 20.5 oz (606 g). Babies of mothers with a smaller storage capacity will need to feed more frequently. These babies get less milk with each feeding because the breast holds less milk. Nancy Mohrbacher has created an infographic to help explain "breast storage capacity." It shows how two healthy breastfed babies of the same age can have very different nursing patterns. Both of these nursing schedules are "normal.” Follow your baby's feeding cues, rather than a schedule. This will let you and your baby work out a feeding pattern that fits your breast storage capacity.

Larger breasts
Breast size may influence nursing in the early days as you and your baby learn to breastfeed together. If you have very large breasts, you may find it more challenging at first. It may be difficult positioning your baby for a good, effective latch. It may be harder to see if your baby is latched on deeply. The size and shape of your breasts (larger or smaller) may also influence the position you find most comfortable for holding your baby at the breast. Ask for help if you can’t find a position that works well. See Positioning and Latching.

Insufficient Glandular Tissue (IGT)
In some rare cases, breasts do not develop fully during puberty. This is known as having insufficient glandular tissue (IGT) or mammary hypoplasia. This means there is not enough glandular tissue to produce all the milk a baby needs.

Signs that you might have IGT include:

  • Widely spaced breasts (more than 4 cm or 1.5 inches apart).
  • Significant difference in size between your two breasts.
  • Tubular or cone-shaped breasts. Bulbous areolas.
  • Very little tissue on the underside of the breasts. This often makes the areolas of the breast point down to the ground.

Nursing parents with IGT often report that their breasts did not change at all during pregnancy. They may also notice very little change in their breasts after birth.

If you suspect that you might have IGT, consult your healthcare provider for a diagnosis. Most mothers with IGT are able to produce some milk. However, most are not able to produce a full milk supply. For these women, supplementation with donor human milk or formula will be necessary. See How to Protect Breastfeeding While Supplementing. You may find this disappointing. A La Leche League Canada Leader can provide you with information and support on your journey. It can be helpful to remember that any amount of your milk that you are able to give your baby is beneficial for both you and your baby. You’ll find support and information at La Leche League Canada meetings.

Regardless of your breast size, if you have questions or concerns about milk production, frequency of feedings or positioning and latch, please contact a La Leche League Canada Leader to get more information and support. Because breastfeeding isn’t always easy, we’re here to help.

If you have found this information sheet helpful, please consider making a donation to LLLC.

Mohrbacher, Nancy. (2020). Breastfeeding Answers: A Guide for Helping Families, Second Edition. Nancy Mohrbacher Solutions, Inc, pages 416-418, 785-787.

Updated December 2022