Many breastfeeding parents notice one breast produces more milk than the other. While this can cause concern, it is common and often normal. Understanding the reasons behind this asymmetry can provide reassurance.
How Milk Production Normally Works
Lactation is a complex biological process driven by hormones and a supply-and-demand system. During pregnancy, hormones like estrogen and progesterone prepare the breasts. Mammary glands contain tiny alveoli where milk is produced and stored. Contractile cells surrounding alveoli push milk into ducts leading to the nipple.
After birth, placental delivery causes a sharp drop in progesterone, allowing prolactin, the primary milk-making hormone, to increase. This triggers copious milk production, often called milk “coming in.” Suckling stimulates nerve endings, signaling the brain to release prolactin for milk production and oxytocin for the “let-down” reflex. More milk removed signals the body to produce more, demonstrating the supply-and-demand principle.
Common Reasons for Uneven Milk Supply
Many everyday factors contribute to uneven milk supply. A common reason is a baby’s preference for one side. Babies might latch or feed more vigorously on one breast, increasing stimulation and milk production there. This consistent preference creates higher demand, naturally increasing supply.
Parental habits also influence uneven supply. Consistently offering one side more often, for comfort or habit, leads to greater stimulation and milk removal, boosting its production.
Previous breast issues like mastitis, engorgement, or blocked ducts can affect a breast’s milk-producing capacity. Nipple damage or soreness on one side can make feeding painful, causing less effective feeding. This reduced stimulation decreases milk supply. Natural anatomical variations are also a cause; one breast may have more glandular tissue or active milk ducts. Pumping habits also play a role, as more frequent or effective pumping on one side increases output.
Less Common Medical Considerations
While many causes of uneven milk supply are benign, certain medical conditions contribute. Prior breast surgeries, including augmentation, reduction, or biopsies, can impact milk production by severing ducts or damaging nerves. The impact depends on surgical technique, incision location, and glandular tissue affected.
Insufficient Glandular Tissue (IGT), or mammary hypoplasia, is a condition where milk-making tissue did not develop adequately. This can result in lower milk supply, sometimes more pronounced in one breast. Nerve damage, from surgery or injury, can interfere with signals for milk production and let-down.
Hormonal imbalances, like PCOS or thyroid abnormalities, can affect milk supply, potentially impacting one breast more noticeably. Retained placental fragments after birth can inhibit milk production because the placenta secretes progesterone, suppressing prolactin. This can lead to a noticeable impact on one side or a general delay in milk “coming in.”
Navigating Uneven Production and When to Seek Help
Several strategies can help balance uneven milk supply. Start feeds on the less productive breast when the baby is hungriest to encourage vigorous nursing. Offer that breast more frequently to increase demand and supply. Ensure a deep, effective latch on both breasts to maximize milk transfer and stimulation. Targeted pumping after feeds on the less productive side, or adding extra sessions, can further signal the body to produce more milk.
Monitoring the baby’s well-being is important with uneven supply. Consistent weight gain, adequate wet and dirty diapers, and contentment after feeds indicate the baby is receiving enough milk. If uneven supply is primarily a cosmetic concern and the baby is thriving, intervention may not be necessary.
However, clear indicators exist for seeking professional help. If the baby is not gaining weight adequately, if persistent pain occurs during feeding, or if signs of infection like redness, warmth, or fever develop, professional medical advice is warranted. Other reasons to consult a lactation consultant or healthcare provider include feeling a breast lump, experiencing significant breast size or firmness differences causing discomfort, or if the baby completely refuses one breast. Many parents successfully breastfeed even with uneven production, and professional guidance provides personalized support and reassurance.