What signifies engagement in the labor process?

Engagement in the labor process refers specifically to the moment when the presenting part of the fetus, typically the fetal head, enters the pelvic inlet and becomes fixed in the pelvis. This is a crucial step as it signifies that the fetus is adapting to the shape of the maternal pelvis and is in a position to proceed further down the birth canal during labor.

The descent of the fetal head signifies engagement, as it indicates that the fetus has moved from a floating position to a more engaged position within the pelvis, thus preparing for delivery. This moment is important for assessing fetal position and determining the progress of labor.

The other options describe different aspects of labor. The onset of contractions marks the beginning of the labor process but does not necessarily indicate engagement. The rupture of membranes is a significant event that can occur at any time during labor, sometimes before engagement, and does not specifically signify it. Similarly, changes in fetal heart rate can reflect various conditions of the fetus during labor but do not directly indicate engagement.