What is Dilation in Pregnancy?

When you’re preparing for labor and delivery, “dilation” becomes a very important term because it measures how close you are to delivering your baby. For example, when you’re about 4 centimeters dilated you may receive an epidural. When you are 10 cm dilated you are ready to deliver your baby.

What is dilation?

Dilation is when your cervix opens (dilates) and the opening is measured in centimeters. During the first stage of labor, the cervix opens and thins out (effaces) to allow the baby to move into the birth canal. During the second stage of labor, your cervix is fully dilated, your baby is descended down the birth canal and you will be encouraged to push and deliver your baby.

What causes dilation and effacement?

When your baby starts to drop down into your pelvis this puts pressure on your cervix causing it to efface and open up in preparation for labor.

When labor begins, contractions of the descent of the baby will cause your cervix to fully dilate, allowing your baby to enter the birth canal and be delivered. Cervical dilation may happen naturally or be induced.

When do you start dilating?

The timing is different for every woman. As you get closer to your due date, your cervix may start to dilate without you knowing it.  Dilation is a gradual process that, for some can take weeks, even up to a month. Others will dilate and efface overnight.

Phases of Dilation

Here’s what’s going on as you progress through labor and how to visualize the opening of your cervix.

Early Phase: Your cervix dilates 1-3 cm with mild contractions.

  • 1 cm dilated = Cheerio
  • 2 cm dilated = Grape
  • 3 cm dilated = Banana Slice

Active Phase: The cervix expands from 6 to 10 cm and your contractions become more regular and intense.

  • 4 cm dilated = Cracker
  • 5 cm dilated = Lemon Slice
  • 6 cm dilated = Cookie
  • 7 cm dilated = Orange Slice
  • 8 cm dilated = Halved Apple
  • 9 cm dilated = Donut
  • 10 cm dilated = Melon

Symptoms of Dilation

Other than a physical exam by your healthcare provider, symptoms you’re beginning to dilate include:

  • Losing your mucus plug: During pregnancy, the opening of the cervix is blocked by a thick plug of mucus to prevent bacteria from entering the uterus. During dilation, this plug is loosened. It may come out as one piece or as thick mucus discharge from the vagina. When this occurs, it is an indication that the cervix is beginning to dilate, although not all women will notice this mucus plug being released.
  • Having a bloody show: This usually comes along with the mucus plug and may continue throughout labor, making the mucus tinged pink, red, or brown. Fresh, red blood is usually not associated with dilation, but rather with serious complications such as placental abruption (when the placenta detaches partly or entirely from the wall of the uterus) or placenta previa (when the placenta attaches low within the uterus, covering all or part of the cervix).