At which station is the fetal head considered engaged?

The point at which the fetal head is considered engaged corresponds to station zero. Engagement occurs when the largest diameter of the fetal head has descended into the pelvic inlet and is aligned with the ischial spines, which are anatomical landmarks within the pelvis. This is clinically significant because it indicates that the fetus is positioned in a way that facilitates descent into the birth canal, essential for successful labor progression.

When the fetal head is at station zero, it is no longer floating above the pelvic inlet, and this engagement is a crucial step in the labor process, often indicating that the mother is in the progressing stages of labor. In contrast, stations above zero (like -1, +1, and +2) indicate varying degrees of descent relative to the ischial spines, with negative stations representing positions above the pelvic level and positive stations indicating further descent towards the vaginal opening but not signifying engagement.