Pregnancy and lactation spark numerous changes in a woman's body, and some of these changes can be uncomfortable or jarring. It's common for breastfeeding women to feel a sensation of heaviness in their breasts and chest. As the breasts fill with milk, they exert pressure on the surrounding tissue and muscles which can cause a feeling of heaviness and even lead to back pain and muscle soreness. In most cases, chest heaviness is not cause for concern, but you should consult your doctor or a lactation specialist about any breastfeeding concerns.
The let-down reflex typically occurs after a baby has been nursing for a minute or two, but can also be a response to a crying baby, pediatrician William Sears explains in "The Breastfeeding Book." You may notice that your breasts feel heavier, tingly or warm when this occurs, and many women feel an overwhelming urge to breastfeed. Women who do not continue breastfeeding when the let-down response occurs may leak small quantities of milk.
Breast engorgement is the most common cause of painful chest heaviness in breastfeeding women, according to Sears. This occurs when your milk supply and your baby's nursing schedule have not yet lined up, and is especially common in the first few weeks after delivery. Encourage your baby to breastfeed when your breasts are engorged or use a breast pump to pump milk and relieve the painful feeling of fullness.
Your breast size can increase by several cup sizes during breastfeeding. This change can be painful and cause strong feelings of chest heaviness, particularly for women with small breasts. A supportive nursing bra can help your body adapt to the change. Stretch frequently and practice good posture with a straight back to prevent your breasts from injuring back and neck muscles.
If your breasts are swollen and red, you may be suffering from mastitis, a painful breast infection. This infection can cause fevers and, in very rare cases, become life-threatening, so consult your physician immediately. Sometimes chest heaviness is merely coincident with breastfeeding. If you feel pressure in your chest, numbness or tingling in your left shoulder or arm, or you feel light-headed, this could indicate heart problems, so call your doctor or go to an emergency room immediately.