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.

How long can you be effaced before labor?

Some women may reach 100% effacement within a few hours. For others, cervical effacement may occur slowly over several weeks. The same applies to dilation. It is not uncommon for a woman to be 1–2 cm dilated a couple of weeks before going into labor.

Can you be 100% effaced and not in labor?

This probably isn't the answer you want to hear, but you can be varying degrees of dilated or effaced for several days — or even weeks — before true labor begins. Alternatively, you might not be dilated or effaced at all and still go into labor within hours. First-time moms tend to efface before they dilate.