The final step in the mechanism of labor is Expulsion, which involves the complete delivery of the fetus through the birth canal. This stage follows after the fetus has descended, engaged, and undergone necessary movements such as flexion. Expulsion signifies the actual passage of the fetal shoulders and body through the vulva, culminating in birth. It is the critical endpoint of labor where the newborn is fully delivered, allowing immediate neonatal care and assessment.

Reference: Williams Obstetrics, Cunningham et al., 25th Edition.