What marks the end of the third stage of labor?

Choice A rationale Engagement of the head, where the widest part of the fetal presenting part descends to the level of the maternal ischial spines (station 0), is a landmark of the first stage of labor, specifically during the descent phase, and occurs well before the third stage concludes. Choice B rationale Full cervical dilation (10 cm) signals the end of the first stage of labor and the beginning of the second stage. This achievement permits the passage of the fetal head and body through the birth canal, an event that precedes the third stage. Choice C rationale The third stage of labor begins immediately after the birth of the infant and is complete with the expulsion of the placenta and fetal membranes. This is a critical process involving uterine contraction to shear the placenta from the uterine wall and prevent postpartum hemorrhage. Choice D rationale The birth of the infant marks the end of the second stage of labor, which begins with full cervical dilation. The subsequent stage, the third stage, is dedicated to the process of placental separation and expulsion.