IBCLC Practice Exam 2026 – Complete Preparation Guide

Lactogenesis II, also known as "the onset of copious milk secretion," is primarily triggered by the expulsion of the placenta, which results in a significant drop in progesterone levels. During pregnancy, high levels of progesterone inhibit lactation by preventing milk production. Once the placenta is delivered, progesterone levels decrease rapidly, allowing the hormone prolactin to stimulate milk production.

This process is crucial because it marks a transition from the preparatory phase of lactogenesis I, where the breasts undergo changes to prepare for milk production, to the active production of milk needed for breastfeeding. The timing and hormonal shifts involved are critical for establishing a successful breastfeeding relationship and for providing the newborn with the necessary nutrients.

While increased estrogen levels, first breastfeeding sessions, and increases in prolactin do play roles in lactation, they are not the primary triggers for lactogenesis II. The expulsion of the placenta and the associated hormonal changes are essential for the initiation of this phase of lactation.