Dilation of the Cervix in Late Pregnancy

Illustration of cervical dilation in the first stage of labor

Verywell / Alison Czinkota

In most pregnancies, the cervix remains long and closed until late in the third trimester. At this point, your baby starts to drop down into the pelvis. This puts pressure on the cervix, causing it to thin out (or efface) and open up (or dilate) in preparation for labor. Once labor begins, contractions and the descent of the baby will cause your cervix to dilate fully, allowing your baby to enter the birth canal and, ultimately, be born.

Measuring Cervical Dilation

Cervical dilation is measured in centimeters. Your cervix must dilate from zero to 10 centimeters before your baby can be born.

As you get closer to your due date, your cervix may start to dilate without you realizing it. Your doctor or midwife will be able to tell if this is happening when they do a routine cervical check.

Some providers will check your cervix between the 35th and 37th weeks of pregnancy, when they do your group B strep (GBS) screening. Other providers will wait until closer to your due date, or only check your cervix if you are having some contractions.

At 1 cm dilated, the cervical opening is approximately the width of your index finger. When it gets to 10 cm, with the help of contractions during active labor, it will be about the width of a large bagel.

The big question you may have about being dilated is whether or not that means that your baby is likely to be born soon. While being dilated is certainly a positive step towards labor, in and of itself it is not a sign of labor or even that labor is coming in a certain amount of time.

When Dilation Occurs Too Soon

In around 1% of pregnancies, the cervix begins to open well before the pregnancy has gone to term. When the cervix dilates painlessly without any contractions, it is a condition called "incompetent cervix." Having an incompetent cervix often leads to a pregnancy loss or miscarriage in the second trimester, or a very early preterm birth.

An incompetent cervix can be caused by damage during surgeries that involve the cervix (such as a LEEP procedure, dilation and curettage or abortion, damage during a previous birth, or congenital abnormalities). An incompetent cervix is not routinely checked for during pregnancy and therefore is not usually diagnosed until after a second or third-trimester pregnancy loss has occurred.

If you or your doctor suspect that you may have an incompetent cervix, your doctor can evaluate you early in pregnancy. Usually, a diagnosis can be made by serial ultrasounds used to measure the cervical opening and the length of the cervix.

If an incompetent cervix is caught early enough, a procedure known as a cerclage, in which the cervix is stitched closed, can be performed. This treatment may prevent pregnancy loss or preterm birth.


In addition to dilating, your cervix will also start to efface late in pregnancy. Effacement refers to how thick or thin your cervix is. Prior to pregnancy and into much of the third trimester, your cervix is long and thick. As labor nears, it begins to shorten and thin out.

Effacement is generally measured in percentages by doctors and midwives. When you have an exam, your provider may tell you that your cervix is anywhere from 0% to 100% effaced. When your cervix is completely effaced, it effectively becomes part of the uterine wall, allowing the baby to pass through.

Dilation and the Stages of Labor

The first stage of labor—which is followed by pushing—is typically divided into three phases known as early, active, and transition. Stage one is complete when the cervix has dilated to 10 centimeters.

Cervical Dilation in the First Stage of Labor

  • Early phase: The cervix will dilate from 1 cm to 3 cm with mild contractions.
  • Active phase: The cervix expands from 4 cm to 7 cm and contractions become more intense and regular.
  • Transition phase: The cervix dilates to 10 cm. Transition ends when the cervix has reached 10 cm and is fully dilated.

A Word From Verywell

While being told you're dilated toward the end of your pregnancy is exciting, keep in mind that it doesn't necessarily mean labor is imminent. You can walk around for weeks with your cervix at 1 cm, or go from zero to 10 cm over the course of one day. Talk to your practitioner if you have any questions or concerns about this important precursor to your baby's birth.

3 Sources
Verywell Family 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. Cleveland Clinic. Labor and delivery.

  2. Brown R, Gagnon R, Delisle M-F, et al. Cervical insufficiency and cervical cerclageJ Obstet Gynaecol Canada. 2013;35(12):1115-1127. doi:10.1016/S1701-2163(15)30764-7

  3. Yale Medicine. Cervical insufficiency.

By Robin Elise Weiss, PhD, MPH
Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor.