During pregnancy, your cervix is thick and around 3-5 centimetres in length.
As you get close to the end of pregnancy, your cervix begins to shorten and thin.
This process that is referred to as effacement.
Usually the cervix is firm and can feel like the end of your nose.
When effacement begins, the cervix begins to feel softer and feels like a dimple.
The position of your cervix during pregnancy is usually posterior — which means it is pointing toward your back — or in the mid position, which is easier to reach. As the cervix begins to efface and prepare for labour, it will move forward (anterior).
The changes to the cervix can happen over weeks before labour begins, or they can happen just before labour starts. Every woman is unique, but usually, first time mothers will experience effacement before dilation.
In subsequent pregnancies, it is more common for some dilation to occur before effacement.
How Is Effacement Measured?
Measuring cervical effacement means having a vaginal examination. Your care provider will use a sterile glove and insert two fingers into your vagina to reach your cervix.
The cervix actually hangs down into the vagina. Before effacement begins, there is usually around 3-5 centimetres of cervical rim extending downward. As effacement occurs, the cervix is drawn up into the lower part of the uterus, and there is less cervical rim. Eventually it will seem to disappear into the uterus.
Measurements of effacement are referred to in percentages. If there is no change, your care provider will note 0% effacement. If your cervix is half its ordinary thickness, this would be noted as 50% effacement. When you are 100% effaced, your cervix has thinned completely.
What Causes Effacement?
Toward the end of pregnancy, your body begins to produce a hormone called prostaglandin. This hormone acts on the cervix to soften it, allowing it to stretch and dilate.
You may be familiar with the sensation of Braxton Hicks contractions. Most pregnant women experience them in the second or third trimester. In the final weeks of pregnancy, Braxton Hicks may become more intense and stronger, helping to move the baby into a good position, as well as engaging the head into the pelvis. This encourages pressure on the cervix, and promotes more effacement. While engagement isn’t necessary before labour begins, it is quite common for the baby’s head to drop into the pelvic brim to some degree during the last weeks of pregnancy.
What Happens After Effacement?
As your cervix thins completely, at some point uterine contractions will begin. These contractions will be different to Braxton Hicks, as they will begin to dilate (open) the cervix, in order for your baby to make an entrance into the world.
Early contractions may be irregular and mild, but over time they will strengthen and become more regular. Early stages of labour can take some time until the cervix is dilated to around 6 centimetres. At this stage contractions can intensify and get closer together, dilating the cervix more rapidly. Once the cervix is completely dilated (10 centimetres), expulsive contractions will push the baby down into the birth canal to be born.
What If I Am Not Effaced?
In a perfect world we would not be concerned about whether a cervix is effacing or not. In today’s birth culture, there is so much focus on when guessing when labour will begin and what to do if it doesn’t start ‘on time’.
In some situations, having your baby earlier might be necessary. If you wish to avoid an induction, you may prefer to try preparing your cervix with one of these methods:
- Sex: sperm has prostaglandins which can encourage the cervix to begin to thin. This method is safe unless your waters have broken or you have begun to lose your mucus plug, as it increases the risk of infection.
- Evening primrose oil (EPO): many midwives recommend EPO as a ripening agent for the cervix. EPO has substances in it that your body changes into prostaglandins. You can take the oil orally in a capsule or rub the oil directly onto the cervix in the last few weeks of pregnancy. The capsules can also be placed inside the vagina at night (pop on a pad so you don’t get oil on the sheets). Evening primrose oil is not recommended for women who have had vaginal infections, placenta previa and other pregnancy complications.
- Optimal fetal positioning: keeping your body in balance and in a good position encourages baby to move into a head down, tucked chin position. You may like to have body therapy such as massage or osteotherapy, to have your pelvis aligned and ligaments released which may be holding baby in a high position. Sitting upright and walking can encourage baby into a good position and allow them to engage and encourage effacement.
Cervical effacement is an important part of labour and can take some time. Many care providers perform cervix checks during the last weeks of pregnancy to determine how likely it is you will go into labour. What your cervix is doing at that particular moment doesn’t predict what your cervix will be doing in the next few hours, days or weeks. If your cervix is thinning, it can safely do so without needing to be checked. You are more likely to avoid an induction if you avoid having a cervical examination during the final trimester.
Recommended Reading: When Should A Baby Engage In Pregnancy?