Normally, your cervix—the opening to your uterus—is tightly shut. That’s a good thing; your cervix keeps baby “in” while you’re pregnant. But obviously, baby eventually needs to come out. That’s where dilation comes in.
At the end of your pregnancy, your cervix starts to open up—this is dilation. Leading up to and during the course of labor, your cervix will dilate to around 10 centimeters, which is about equal to the diameter of a softball. (Or, not-so-coincidentally, a baby’s head.)
Some women begin dilating before they start active labor—that’s why you sometimes hear about women who are 3 centimeters dilated but not yet in labor. The bulk of dilation happens during active labor, though, and being slightly dilated before labor is not at all a reliable indicator of how quickly labor will progress. Every woman dilates at a different rate.
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