stages of labor The process of expulsion of the fetus and the placenta from the uterus. The stages of labor include: first stage, beginning with the onset of uterine contractions through the period of dilation of the os uteri; second stage, the period of expulsive effort, beginning with complete dilation of the cervix and ending with expulsion of the infant; third stage or placental stage, the period beginning at the expulsion of the infant and ending with the completed expulsion of the placenta and membranes. [L. toil, suffering]