Large differences between breasts

How does a large difference in the size of my breasts affect breastfeeding?

A slight difference in size between one breast and the other is normal and does not affect breastfeeding. A major difference may indicate a problem in the smaller breast that has been caused by developmental or genetic conditions. Surgery and trauma can also damage a breast. The smaller breast may never make much milk. In this case, the normal, bigger breast often compensates for the less productive one. It is also possible for a breast to reduce the amount of milk it makes after the baby’s birth. Mothers need to make sure that the baby takes in enough milk. Babies may become reluctant to breastfeed on the smaller side or reject it completely.

A) Small differences in breast size

Most mothers have one breast that is slightly larger than the other. This is normal and does not cause problems breastfeeding. Mothers should treat both breasts equally and change the starting side.

B) Large differences in breast size

A major difference in breast size may be a sign that the smaller breast has a problem and may not be able to make enough milk.

Having one breast with a low milk supply can lead to the baby not taking in enough milk. In addition, babies frequently prefer the more active breast and may become reluctant to breastfeed on the weaker side or may even reject it completely. Mothers should start all feeds on the weak side to ensure the baby stays interested in both.

1) Problems in one breast that develop before giving birth

A breast may be small because of a problem that developed before or during the current pregnancy:

2) Problems in one breast that develop after giving birth

Other problems can arise in one breast once breastfeeding has started and can reduce overall milk production.

A mother who develops breast cancer while breastfeeding may notice an increase in breast size because of swelling or tumour growth or a decrease in milk supply on the affected breast. 


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