a. Stage I. Stage I of labor is characterized by regular contractions of the uterus
as well as other physical changes. The contractions become increasingly more intense
as labor proceeds. Oxytocin, a hormone produced in the neurohypophysis, is usually
released to cause the onset of uterine contractions.
b. Stage II. Stage II of labor is characterized by the actual delivery of the
c. Stage III. Stage III of labor is characterized by the expulsion of the afterbirth
(placenta, amniotic sac, and membranous tissue contained in the uterus).
Figure 11-1. The stages of labor.