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Cervical effacement and dilation
During the first stage of labor, the cervix opens (dilates) and thins out (effaces) to allow the baby to move into the birth canal. In figures A and B, the cervix is tightly closed. In figure C, the cervix is 60 percent effaced and 1 to 2 cm dilated. In figure D, the cervix is 90 percent effaced and 4 to 5 cm dilated. The cervix must be 100 percent effaced and 10 centimeters dilated before a vaginal delivery.