IBCLC Practice Exam 2025 – Complete Preparation Guide

Lactogenesis I, also referred to as secretory differentiation, describes the initial phase of milk production that occurs during pregnancy and just after birth. During this stage, the mammary glands undergo significant developmental changes to prepare for the secretion of milk. Secretory differentiation involves the maturation of the alveolar cells in the breast, which begin to produce and secrete milk, specifically colostrum, in response to hormonal changes induced by the delivery of the placenta.

This period is critical as it ensures that the breast is fully prepared to begin the next phase of lactation, which is Lactogenesis II, when milk volume increases and mature milk is produced. While colostrum formation is a component of this process, referring to lactogenesis I as secretory differentiation more accurately captures the broader physiological transformations occurring within the breast tissue.

Mammary engorgement and the milk ejection reflex relate more to subsequent stages of lactation rather than the initial differentiation phase, making them less applicable in this context.