Cervical Dilation and Effacement

Learn about what causes your cervix to start opening and thinning at just the right time in your pregnancy.

Dilation, the opening of the cervix (measured in centimeters), and effacement, the thinning of the cervix (measured in percentage), occur in a pregnant woman as labor and delivery get closer. The timing is different in every woman: For some, dilation and effacement is a gradual process that takes weeks or even a month; others can dilate and efface overnight. (Sorry, but wishing won't make it so.)

What causes it

Your cervix is preparing for delivery by providing an opening from the uterus to the birth canal — unblocking the path to your baby's exit route.

What you need to know

Beginning in your ninth month of pregnancy, your practitioner will look for clues that labor is getting closer, palpating your abdomen and giving you an internal exam to check your cervix. In addition to seeing if baby's "dropped," she's confirming whether your cervix has dilated and effaced and if it's begun to soften and move to the front of the vagina (another indicator that labor is getting closer). Based on these factors, she'll likely make an educated guess as to when you'll deliver. But don't go racing to the hospital just yet if that guess is "soon": For every practitioner who's right on the money, there are a hundred women who are still pregnant — and impatient — a week later.

As the cervix continues to thin and open, the "cork" of mucous that seals the opening of the cervix (otherwise known as the mucous plug) becomes dislodged. You may or may not notice it happen (depending on whether or not you're the flush and rush type), and it can occur anywhere from a couple of weeks to hours before labor starts. Then a few days to 24 hours before delivery day, you'll notice bloody show as the capillaries in your cervix begin to rupture, tinting vaginal mucous pink or streaking it with blood. When labor contractions get progressively stronger and don't go away even when you change positions, you'll know it's finally show time!

Throughout this process, your cervix will keep on effacing and dilating. In early labor (those days to possibly weeks before it's time to go to the hospital), your cervix will dilate to about 3 cm; by active labor it will increase to 7 cm. Full cervical dilation — when your cervix measures 10 centimeters — occurs at the end of the transitional phase (the last of the three phases of labor). Once this happens, it's time to start pushing your baby out.

What you can do about it

Not a thing: Your body is in charge here. Once your doctor gives you that estimate for baby's arrival, just keep an eye out for other signs of labor so you'll know and be prepared when it's time to go to the hospital. Occasionally if labor stalls or if you have certain risk factors, your practitioner may determine there's a reason to induce labor and will take steps to move the process along.