27 facts about the cervix and how it acts during labor

    1. When it is close to time to deliver your baby, the cervix starts to efface, or thin, and dilate, or open. This is to prepare for the baby to go through the birth canal.
    2. The rate at which cervical dilation and effacement happens is different for each woman.
    3. Sometimes, this process takes place slowly over weeks prior to the delivery, and new mothers often dilate and efface during active labor. Often, your doctor may use gloves to check and see how far you have effaced and dilated.
    4. The cervix is the lower, narrow part of the uterus, where it connects with the top area of the vagina. To see some great images of the anatomy of it, please visit the beautiful cervix project site.
    5. It is either cylindrical or conical-shaped, and pushes through the upper vaginal wall. With the right equipment, doctors can view half of its length.
    6. The part of the cervix that protrudes into the vagina is called the ectocervix.
    7. It is usually 3 cm in length and 2.5 cm wide.
    8. The surface is elliptical, convex, and has anterior and posterior lips.
    9. The opening of the ectocervix is known as the external os.
    10. The shape and overall size of the organ is dependent on age, hormones, and if the woman has given birth vaginally or not.
  • In women that have yet to give birth, the external os looks like a small, round opening.
  • In women that have had a vaginal birth, the ectocervix looks thicker, and the external os is wider.
  • The endocervical canal is the passageway linking the external os and the uterine cavity. It‘s width and length is much different in each woman. It is flattened front to back, and the endocervical canal is about 7 to 8 mm at its widest, and this is usually seen in women of childbearing age.
  • When the baby’s head drops down into the pelvic region, the stress on the cervix causes it to thin out, or efface.
  • During your entire pregnancy, a mucus plug protects your cervix.
  • When the cervical effacement begins, the plug is pushed out, and known as show, or bloody show.
  • Some women may not even notice this.
  • Doctors talk about effacement as a percentage. If there is no cervical effacement, then it is zero. If it is totally thinned, it is at 100%, and considered completely effaced.
  • After the cervix has started to efface, it will also begin to open, or dilate. This is expressed in centimeters from 1 to 10. Zero is when it is closed, and 10 means that is it fully dilated.
  • When you are in your first labor stage, contractions from the uterus assist your cervix in effacing and dilating, to help your baby make it through the birth canal.
  • At the beginning, your contractions are far apart, but after time, they become more regular, usually every 2-3 minutes and lasting for between 45-60 seconds in length.
  • In the second labor stage, you will experience much stronger contractions about every 2-3 minutes and lasting between 60-90- seconds. At this time, your doctor will tell you to push, or bear down when you have a contraction. Pain is intense during this time, so rest when possible is encouraged. By now, your cervical effacement will be 100%, and your cervical dilation will be at 10.
  • Before labor starts, the cervix drops into the vaginal canal, so that it is facing in the direction of the back. This generally occurs during early labor.
  • Effacement and dilation work hand in had to widen the cervix to allow the baby to drop into the vagina. When you are pregnant, the cervix thickens and gets longer to shield the baby. When you are in labor, cervical dilation and cervical effacement occurs, so that the baby can pass through the birth canal.
  • In labor, the cervix opens wide so that the baby can get through. Your cervix will need to be effaced before any real degree of dilation will occur.
  • The baby’s station is talking about the movement of the baby’s head through the pelvis. Usually, the baby’s head position is measured using the narrow part of the pelvis. Prior to the baby’s head getting to the narrow part of the pelvis, the station of the baby is presented in numbers that are negative. When the head goes past the spinal area, then the station is given in numbers that are positive.
  • Many times, during managed labor, cervical checks will be done to see how far cervical dilation has occurred. When in active labor, this process can be very painful, as women are made to lie on their backs, which is the most uncomfortable position to be in when one is in labor. Also, cervical checks increase the risk for infection, since the mucus from the cervix is used to wash away bacteria down and out of the birth canal, and fingers used to check for dilation effectively push the bacteria back in. Usually, if the bag of waters has burst, this will not be done more than once or twice, as it poses a serious infection risk. So, use diligence when you feel this is unnecessary!


When you know more about cervical dilation and cervical effacement, it can make your labor a little less confusing, and allow you to know more about what is going on with your body during labor.