What Is Dilation in Pregnancy?

Dilation is the opening of the entrance to the womb. It happens during labor.

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Dilation is the process by which the cervix opens during childbirth. The cervix is the lower part of the uterus, where it opens to the vagina.

During labor, contractions cause the cervix to change from being closed to fully dilated or open to 10 centimeters. Once that happens, it’s time to begin pushing.

Read on to learn more about dilation during pregnancy, including how dilation is measured, symptoms, phases, and more.

Healthcare provider checking dilation on a pregnant person

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How Dilation Is Measured

Dilation is measured in centimeters. For most of the pregnancy, the cervix is closed. However, as labor approaches, the cervix opens as it begins to prepare for childbirth. Some people become 1-2 centimeters dilated before they start active labor, while others start active labor without being dilated at all. 

When your cervix is fully dilated, the opening will measure 10 centimeters or about 3.9-inches. That’s the same diameter as a large bagel or cantaloupe cut in half. It’s large enough for the baby’s head to pass through. 

Checking dilation

When you are in labor, your healthcare provider will check your dilation through a cervical exam. During this exam, they will insert their gloved finger into your vagina to check how wide the cervix has dilated.

Most people do not find these exams painful, although they can be uncomfortable. Unless there are complications, your healthcare provider will likely check you when you are admitted and before you begin pushing. Checking dilation too frequently can introduce bacteria to the vagina.

Effacement vs. Dilation

In order to birth a baby, your cervix must be thin and open. Effacement refers to how thin the cervix is, which is measured as a percentage. In order to give birth, your cervix must be 100% effaced. This often happens before labor, and you may notice signs, like losing your mucus plug or experiencing more discharge. Once the cervix is effaced, dilation can occur.

Symptoms

Dilation is caused by contractions. These contractions cause the muscles in your abdomen to become very tight, then relax. At first, these contractions may be mild and barely noticeable. As labor progresses, you’ll experience more intense contractions. You’ll also notice other symptoms of active labor, including:

  • Strong, regular contractions that cause pain in your abdomen and back. 
  • Increased discharge, which may be bloody, brown, or contains mucus. 
  • Water breaking or when the amniotic sac ruptures. There may be a gush or a trickle of amniotic fluid, or it may not happen until late in labor. 

It’s normal for contractions to start and stop before true labor sets in. Unfortunately, that can make actual labor hard to spot. Once your contractions last for 30 to 70 seconds and are five to 10 minutes apart, it’s time to call your healthcare provider.

Phases of Dilation

Healthcare providers divide labor into three stages:

  • First stage: During this stage you experience regular contractions, increasing in intensity. All dilation takes place in the first stage of labor. The first stage lasts for many hours. 
  • Second stage: The second stage is when you are actively pushing your baby out. It lasts from minutes to three hours. This stage begins when your cervix is fully dilated. 
  • Third stage: The third stage is the delivery of the placenta, which often takes about 30 minutes. 

It can be helpful to break the first stage down since this is the longest part of labor. The two phases of stage one are:

  • Latent phase: Also known as early labor, this is when your cervix is effacing and starting to dilate. Contractions are regular, starting mild and increasing in intensity. During this stage, dilation will move from 0 to 3-4 centimeters. 
  • Active phase: When your cervix has dilated to 4 centimeters, your contractions will likely become more intense. They’ll last longer and come closer together, which will help you dilate to a full 10 centimeters. 
I'm dilated

Verwell / Alison Czinkota

Complications

While dilation is a natural process, it doesn’t always go seamlessly. Some people experience complications with dilation. If your cervix cannot fully dilate, your healthcare provider may suggest a cesarean delivery (C-section). 

Induced Dilation

Sometimes, your healthcare provider might decide that inducing labor, or artificially jump-starting it, is what is healthiest for parent and baby. This may happen if:

  • You’re more than two weeks past your due date
  • Your water broke, but labor didn’t start
  • You have health concerns, such as high blood pressure or low amniotic fluid

If you need to be induced, your healthcare provider will likely use various means to encourage dilation and the start of labor. These may include:

  • Using the hormone prostaglandin causes the cervix to soften and efface. Prostaglandin can be taken orally or inserted into the vagina. 
  • Using the hormone oxytocin (in the form of the medication Pitocin) to induce contractions, which cause dilation. 
  • Using a Foley Bulb induction, where a catheter is inserted into the cervix. The catheter is slowly injected with saline solution, putting pressure on the cervix and causing it to open.

When Dilation Happens Too Early

If labor starts before 37 weeks, it is considered preterm labor. A fetus born too early faces risks, including death and serious illness. If you’re experiencing early dilation, your healthcare provider might suggest treatments to try and reduce your risk of preterm labor. They may also provide steroids that will help your baby’s lungs develop in case they are born early. 

The treatments for preterm labor include:

  • Progesterone: When given as a shot or inserted into the vagina, this hormone can reduce the risk for preterm labor. 
  • Cerclage: If your cervix begins to dilate very early, your healthcare provider may use stitches to sew the opening closed. This is known as cervical cerclage. The stitches are removed at 36 weeks gestation, allowing for normal dilation during labor. 

Your healthcare provider may also recommend bed rest or reduced activity to help prevent further dilation.

What Is Cervical Insufficiency?

Cervical insufficiency is a condition that causes the cervix to efface and dilate too early. It’s the cause of about 1% of preterm births.

Summary

Dilation is when the cervix opens during labor as your body is getting ready for childbirth. Contractions of the uterus cause the cervix to dilate. When the cervix measures 10 centimeters, you can begin pushing. If your cervix does not fully dilate, your healthcare provider may try different methods to induce dilation or recommend a C-section. Other times, the cervix may dilate too early, which may lead to preterm labor. Your healthcare provider will try different treatments to prevent further dilation if labor starts before 37 weeks.

A Word From Verywell

Anticipating labor can be both exciting and scary. Knowing what to expect can help you feel more in control, but remember: there's no way to know what will happen when it's time to give birth. Surrounding yourself with trusted healthcare providers and loved ones can help you feel confident when the time comes.

Frequently Asked Questions

  • When does your healthcare provider start checking for dilation in pregnancy?

    Some healthcare providers will check dilation as you approach your due date, but this isn't an indication of how far or close labor is. Most people will have a cervical check when they get to the hospital and before they start pushing.

  • How long does dilation take during labor?

    Dilation can take hours or days. It is highly individualized. As long as your body is making steady progress your healthcare provider will likely allow your body to dilate until you reach 10 centimeters.

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7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. John Hopkins. Labor.

  2. American College of Obstetricians and Gynecologists. How to tell when labor begins.

  3. My Health Alberta. Cervical effacement and dilation.

  4. March of Dimes. Contractions and signs of labor.  

  5. Nemours Kids Health. Inducing labor.

  6. Nemours Kids Health. Treatments to prevent premature birth.

  7. Yale Medicine. Cervical insufficiency.