Before pregnancy, a combination of supportive tissue, milk glands and protective fat makes up a large portion of your breasts. Your breasts also contain a network of canals that will transport milk through your breasts. During puberty, the female hormone estrogen caused your mammary glands to grow and swell. When you get pregnant your mammary glands begin to grow and swell even more.

In the early stages of pregnancy, your breasts began to show physical changes such as tenderness, swelling and the darkening of the nipples and the areolas (circle of skin surrounding your nipple). Your breast contain thousands of sacs lined with special cells that absorb water, salts, sugar and fat from your blood. From these ingredients, your body manufactures your breast milk. Milk flows through a network of canals to reservoirs located behind you nipples. Your milk production becomes developed fully during your second trimester, so you can nurse your baby even if he/she arrives prematurely.

As your body gets ready to breastfeed, it will pump extra blood into your breasts making them firm and full. These swollen blood vessels, combined with a full supply of milk may make your breasts painful and uncomfortable. This is only temporary, and the discomfort will decrease in the first few days with frequent nursing.

Worried you will run out of milk? Don’t. Your breasts replenish the supply of milk as it is needed. You will not run out of milk; your body will continue making the milk as long as your baby is nursing. As your baby suckles on the breast, it creates a sensory stimulation through nerve endings in the nipple that results in milk production. Your breast will never empty while breastfeeding because you are always capable of producing more milk. Tiny openings in your nipples allow your baby to drink your milk.

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