Despite variations in childbirth, there are three generally recognizable stages in the process (see I Figure 11.6). A woman can often tell that labor has begun when regular contractions of the uterus begin. Another indi­cation of beginning first-stage labor, the gradual dilation of the cervix to 10 centimeters, is the "bloody show" (discharge of the mucus plug from the cervix). The amniotic sac can rupture in the first stage of labor, an occurrence sometimes called "breaking the bag of waters." Before the first stage begins, effacement (flattening and thinning) of the cervix has usually already occurred, and the cervix has dilated slightly. The cervix continues to dilate throughout the first stage. The first stage is the longest of the three stages, usually lasting 10 to 16 hours for the first childbirth and 4 to 8 hours in subsequent births.

Second-stage labor begins when the cervix is fully dilated and the infant descends far­ther into the vaginal birth canal. Usually the descent is headfirst, as shown in Figure 11.6b. The second stage often lasts from half an hour to 2 hours—although it can be shorter or longer. During this time the woman can actively push to help the baby out, and many women report their active pushing to be the best part of labor:

I knew what "labor" meant when I was finally ready to push. I have never worked so hard, so willingly. (Authors’ files)

The second stage ends when the infant is born.

Third-stage labor lasts from the time of birth until the delivery of the placenta, shown in Figure 11.6c. With one or two more uterine contractions, the placenta usually separates from the uterine wall and comes out of the vagina, generally within half an hour of the birth. The placenta is also called the afterbirth.