IBCLC Practice Exam 2026 – Complete Preparation Guide

Lactogenesis II refers to the phase of milk production that occurs around the time of birth, characterized by the onset of copious milk secretion. This phase is primarily regulated by endocrine factors.

During lactogenesis II, the hormone prolactin plays a crucial role in stimulating milk production. Prolactin levels increase following the delivery of the placenta, which results in a sharp decrease in estrogen and progesterone levels, thus allowing prolactin to initiate and support lactation. The surge in prolactin is pivotal because it triggers the alveolar cells in the mammary glands to produce and secrete milk.

While autocrine mechanisms also play a role in lactation once milk is established, lactogenesis II is predominantly driven by hormonal (endocrine) changes that occur immediately postpartum. This transition signifies the shift in lactation control from hormonal to autocrine regulation in later stages of lactation, where the presence of milk in the breast sends feedback to adjust milk synthesis based on infant demand.

Neural mechanisms are involved in lactation, particularly during the let-down reflex, but they do not primarily control the initiation of milk secretion in the early stages of lactogenesis II. Thus, understanding the role of endocrine control is crucial for comprehending