You know that your cervix needs to dilate in order for your baby to be born.

But how much do you actually know about how your cervix dilates?

Cervical dilation has become one of the most focused on areas of labor and birth, so it’s important you are aware of exactly what it’s all about.

The cervix is the opening to the womb. It’s located between the vagina and the uterus and plays a crucial role in pregnancy and labor.

During pregnancy, it remains closed and the opening is blocked with a mucus plug.

At the end of pregnancy, your body will experience some changes that will facilitate cervical dilation. One of these changes is the appearance of mucus-tinged pink discharge.

What is dilation of the cervix all about?

Normally, your cervix remains closed and hard. This protects your uterus from the outside environment and any potentially harmful bacteria.

During pregnancy, due to increased blood flow and hormones, slow cervical ripening begins. The cervix begins to change. These changes help the cervix to respond to intense contractions during active labor.

So that your baby can descend through the birth canal and be born, your cervix must thin and open; this process is referred to as effacement and dilation. This happens in the latent phase of labor, before the active phase of labor begins. Irregular mild contractions can contribute to this cervical dilation. It’s not uncommon for women who check their cervix to discover it has begun to open.

Although every woman’s body is different, as a general rule, we tend to say that active labor begins when full cervical ripening (cervical effacement and change of cervical position and consistency) has taken place and the cervix dilates to approximately 4 cms.

Full cervical dilation is a long and gradual process that happens throughout all the various stages of labor – from the early stages until the end of the second stage of labor when a fully dilated cervix allows the baby to descend into the birth canal. When this happens the woman will most likely feel the need to bear down and start pushing her baby out.

What’s all this about centimeters?

Just to be clear, no one will actually measure your cervix. Your care provider will place two fingers inside your vagina (this is called a vaginal examination) and work out how many finger widths fit into the opening of the cervix.

If one fingertip fits, the cervix is considered to be 1 cm dilated. If the tips of two fingers fit, this means the cervix is 2 cm dilated. Depending on the distance the two fingers can stretch apart, it’s possible to indicate further dilation. It is usual to refer to full dilation as 10 centimeters.

If you get a ruler or tape measure, you can stretch your middle and index finger to get an idea of the way your care provider estimates dilation.

Many care providers prefer to do vaginal examinations so they can chart progress against the traditional standard of cervical dilation. This means one centimeter per hour, with active labor beginning at four centimeters. This standard is based on Friedman’s curve, a graph developed in the 1950s, and it still influences routine labor management today.

Does dilation mean I’m in labor?

Dilation on its own isn’t an indicator that you are in the active phase of labor. Many women might be told their cervix is 2-3 cm dilated, yet have no other signs of labor.

Dilation doesn’t indicate when you will go into labor, either.

Your care provider might offer to perform a vaginal examination at an antenatal appointment and tell you your cervix is 3 cms dilated. This doesn’t necessarily mean you will go into labor in the next day or even the next week.

And don’t be disappointed if your cervix is closed and firm; you might go into labor later that day. Every labor is unique and what happens to one woman won’t necessarily happen to the next.

Is a vaginal exam necessary?

Vaginal examinations are optional procedures but many women worry they won’t know how dilated they are during labor if their care provider doesn’t perform one. They wonder how they will know they are in the active stage of labor, or close to pushing.

If your care provider is observing you, it’s possible to note a number of different signs to indicate where you are in labor and guess at your dilation.

Generally, in early labor, women are quite alert and might talk through contractions, which tend to be quite mild at this stage. As labor progresses, the woman will begin to concentrate or focus and stop talking during contractions.

As the cervix gets closer to being fully opened, contractions become longer, stronger, and closer together. The woman will begin to go inwards or possibly become irritable and restless. These usually painful contractions require focus and her breathing will become deeper and stronger to get through each one.

After each contraction, she might go into a meditative state until the next contraction begins. It’s common for a gush of fluid, thick mucus discharge, and bloody show to occur at this stage, as the cervix is probably 6-7 cm dilated.

Pressure might start to increase in the pelvis as the baby begins to descend. When women enter the transition phase they often begin to make different sounds, such as moans, grunts, or low vocal tones. When the cervix is almost completely dilated, contractions are frequent and last about 90 seconds.

There are other physical signs indicating when you are close to, or at, full dilation.

Your care provider can check your fundal height. At full-term pregnancy, there are normally five finger widths between the top of the uterus (fundus) and the bottom of your sternum. When in labor, the uterus is being pulled up or bunching at the top. As dilation progresses, the space between the fundus and sternum gets smaller. When you’re 10 cm dilated there is usually no gap between them.

Many birth workers recognize an earthy or musky smell that women have when they are entering transition (the stage before pushing when the cervix is dilated). There is also the telltale purple line, which extends along the cleft between your buttocks. As the baby descends, increased pressure on blood vessels causes the normally pink line in the cleft to turn purple. The line starts at the anus and moves up. When it has reached the top of the cleft, the cervix is fully dilated.

Find out more in our article Vaginal Examinations – 7 Things You Should Know.

How fast will I dilate?

Even though care providers are still using the Friedman’s curve (1 cm/hour) to decide how labor is progressing, in reality, every woman dilates according to her own body’s rule.

Most hospitals require women to have a vaginal examination to check whether they are in active labor (4 cms or more) before being admitted. Yet a study of over 1300 women showed progress can be slow until around 6 cm, and the slowest rate of cervical dilation was less than 1 cm per hour.

A study in 2012 analyzed over 50 000 normal labors and found dilation appears to accelerate after 6-7 centimeters. The researchers found the rate of cervical dilation from 4 to 6 centimeters was much slower than current standards allowed for. This indicates care providers need to allow more time during the earlier stages of labor, to allow for the variations in dilation rates among women.

What affects dilation?

Effective cervical dilation is dependent on the hormone oxytocin, which stimulates efficient uterine contractions. The uterus draws upwards, which in turn causes the cervix to thin and dilate. It is during this stage of labor women most need to be undisturbed, to promote an increase in oxytocin levels as labor progresses. If a woman is exposed to bright lights, noise, or cold, or has no privacy, her body might start to produce adrenaline.

Adrenaline is released by the body in the ‘fight or flight’ response to a perceived danger or threat. During labor, mammals need to be able to move to safety if threatened. Human beings are no different and, even though we rarely give birth in the wild, the part of our brain that regulates hormone production and threat analysis is unable to distinguish between real and imagined dangers.

As your body makes more adrenaline, you make less oxytocin, and contractions begin to slow down, become irregular, or even stop. World-renowned midwife, Ina May Gaskin, often discusses reversal of cervical dilation occurring when women go to the hospital after laboring well at home for hours. They might encounter staff they don’t like or feel under pressure to have procedures or interventions they don’t want.

Contractions often slow or stall because of rising adrenaline levels. When a vaginal examination shows ‘only’ two centimeters, the woman might be sent home; she might even have her labor augmented, which means she is given medications to stimulate contractions. Once the adrenaline levels descend and oxytocin starts to build up, the contractions will come back and become progressively stronger. If this oxytocin flow is maintained, the first stage of labor will start soon after.

But my cervix wouldn’t dilate

There are factors that can affect your body’s ability to dilate. In most of these situations, there is a way to work through them, rather than consider your body as ‘faulty’.

Some of these factors are:

Adrenaline and stress hormones. Read BellyBelly’s article on Undisturbed Labor and how to limit stress during labor
Malpositioning of your baby. This can affect where your baby’s head is presenting. Practise optimal fetal positioning during pregnancy and choose upright positions during labor
Hormone problems, such as oxytocin deficiency. Although rare, this might be seen in prolonged stressful situations, hypothyroidism, depression, fibromyalgia, autism, and CMV infection
Previous traumatic experiences. These might be previous traumatic birth experiences, or the lasting effects on those who have survived sexual violence.

When these situations can’t be overcome, making an informed decision with the support of her care provider will help a woman give birth safely.

It doesn’t matter where women choose to birth; most will, at some stage, become focused on dilation. You might want to wait until a certain point in normal labor before deciding to have an epidural or letting someone know whether you need a particular person to be available or present.

It’s important to remember that dilation gives us a measurement for the here and now; it has no relevance for comparing your labor with other labors or other women’s experiences, and it can’t predict the future. Cervical dilation is not a crystal ball and can change rapidly from minute to minute.