Physiology and endocrine changes underlying human lactogenesis II.

Lactogenesis stage II, the onset of copious milk secretion, takes place during the first 4 d postpartum in women and involves a carefully programmed set of changes in milk composition and volume. The evidence is summarized that progesterone withdrawal at parturition provides the trigger for lactogenesis in the presence of high plasma concentrations of prolactin and adequate plasma concentrations of cortisol. Although the process is generally robust, delayed lactogenesis does occur with stressful deliveries and in poorly controlled diabetes. Failure of early removal of colostrum from the breast is associated with high milk sodium and poor prognosis for successful lactation in many women. We speculate that this problem may result from accumulation of a substance in the mammary alveolus that inhibits lactogenesis, even in the face of appropriate hormonal changes after parturition.