Breasts often become fuller and tender during pregnancy. This is a sign that the alveoli are getting ready to work. Some women do not feel these changes in their breasts. Other women may sense these changes after their baby is born.
The alveoli make milk in response to the hormone prolactin (proh-LAK-tin). Prolactin rises when the baby suckles. Another hormone, oxytocin (oks-ee-TOH-suhn), also rises when the baby suckles. This causes small muscles in the breast to contract and move the milk through the milk ducts. This moving of the milk is called the \”let-down reflex.\” Learn more about the let-down reflex.
The release of prolactin and oxytocin may make a mother feel a strong sense of needing to be with her baby.