Lactogenesis I: During the second half of pregnancy, the breasts prepare for milk production but high levels of progesterone inhibit milk secretion. Lactogenesis II: Commences around 2-3 days postpartum when the “milk comes in.” Elevated levels of prolactin and decreased progesterone levels lead to the copious production of milk. Lactogenesis III: This ongoing phase involves the maintenance of milk production and secretion, largely dependent on milk removal by the baby or pumping.
