As you get closer to labor and delivery, your cervix will begin to dilate (open up) and efface (thin out). Here's what will happen during — and leading up to — the first stage of labor.
What is dilation?
Dilation is the opening of the cervix, which is measured in centimeters (although your doctor or midwife's fingers actually do the measuring). Once you dilate to 10 centimeters (cm), you're ready to deliver your baby.
When do you start dilating?
You generally start dilating in the ninth month of pregnancy as your due date gets closer. The timing is different in every woman. For some, dilation and effacement is a gradual process that can take weeks or even up to a month. Others can dilate and efface overnight.[1]
What is effacement and what does effaced mean?
Effacement is the thinning of the cervix, which is measured in percentages. When you're 100 percent effaced, your cervix has thinned enough for your baby to be born.
70 effaced
If you're told you're "70 effaced," that means you're 70 percent effaced, so you're roughly three-quarters of the way to where you need to be to have your baby.
80 effaced
If you're "80 effaced," that means you're 80 percent effaced. You're only 20 percent away from being fully effaced at 100 percent, which is when you're ready to deliver.
What causes cervical dilation and effacement?
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 about cervical dilation and effacement
Beginning in your ninth month of pregnancy, your practitioner will look for clues that labor is getting closer, palpating your abdomen and doing an internal exam to check your cervix.
More About Labor
In addition to seeing if the baby's dropped, your doctor is confirming whether your cervix has dilated and effaced and if it's begun to soften and move toward the front of the vagina — another indication that labor is getting closer. Keep in mind, it's not a problem if your baby hasn't dropped just yet; a vaginal delivery is still definitely possible.
Based on these factors, he or she may 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." It's still possible you'll be pregnant — and impatient — a week later.
As the cervix continues to thin and open, the "cork" of mucus that seals the opening (otherwise known as the mucous plug) becomes dislodged.[2] You may or may not notice it happen, 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 the vaginal mucus 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 up to 6 cm; by active labor it will increase to about 7 to 8 cm.
Full cervical dilation — when your cervix measures 10 cm — 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.[3]
What can you do about cervical dilation and effacement?
Not a thing: Your body is in charge here. Once your doctor gives you that estimate for your baby's arrival, just keep an eye out for other signs of labor so you'll know when it's time to go to the hospital.
Occasionally if labor stalls or if you have certain risk factors, your practitioner may decide that there's a reason to induce labor and will take steps to move the process along.
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