Human Growth and Development

Birth and Lactation

What events occur during dilation?

The purpose of dilation is to dilate (open) and thin (efface) the cervix to permit the fetus to move from the uterus into the vagina. Dilation is divided into three phases: 1) the early labor phase, 2) the active labor phase, and 3) transition. During the early phase, contractions last 30 to 60 seconds and occur every 5 to 20 minutes at regular intervals. As labor progresses, the frequency of the contractions will increase. The cervix dilates from 0 to 3 centimeters during the early phase of labor. During active labor, contractions become stronger, last longer (45 to 60 seconds or longer) and occur at more frequent intervals (as frequent as every 2 to 4 minutes). The cervix dilates from 3 to 7 centimeters. The final phase of dilation is transition. During transition, the cervix dilates from 7 to 10 centimeters. It is now fully dilated. Contractions during transition last 60 to 90 seconds with sometimes not even a minute between contractions.


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