The Stages of Labor Onset of labor, the first stage, is heralded
by contractions of the uterus felt as cramplike pains in the
abdomen or lower back that recur at intervals of 10 to 30
minutes and last about 40 seconds; they increase in frequency
until they occur at about 2-minute intervals. With each
contraction the cervix, or neck of the uterus, dilates until it
becomes wide enough, about 4 in. (10 cm), to permit emergence of
the baby. In the second stage of labor the baby passes through
the birth canal, most commonly head first, and is born. The
effectiveness of uterine contractions in this stage is enhanced
by the bearing-down abdominal contractions of the mother. The
third stage of labor, which occurs about 15 to 30 minutes after
the child is born, is characterized by the separation of the
placenta from the uterine wall and its expulsion. The total time
of labor averages 13 to 14 hours in women pregnant for the first
time and 8 to 9 hours in women who have previously borne
children. Sections in this artic