Cervical dilation is the opening of the cervix, the lower part of the uterus, which must widen sufficiently for the baby to pass through the birth canal. Dilation occurs concurrently with effacement, which is the thinning and shortening of the cervix from its typical length to becoming paper-thin. These two changes prepare the body for delivery and are the measurable indicators of labor progression. Understanding these changes helps expectant parents recognize the signs that their body is actively preparing for birth.
The Physical Signs Indicating Labor Progression
The most common sign that labor is beginning is the presence of uterine contractions. True labor contractions differ significantly from Braxton Hicks contractions, which are irregular and fade away with a change in activity or position. True contractions follow a pattern, becoming progressively longer, stronger, and closer together over time. They may feel like intense menstrual cramps, lower abdominal pain, or significant pressure in the lower back, starting mildly and building in intensity.
The loss of the mucus plug, sometimes called the “bloody show,” is another sign of cervical change. This thick, jelly-like collection of mucus sealed the cervix during pregnancy. As the cervix begins to efface and dilate, the plug is dislodged and passes from the vagina. The mucus is often clear, pink, or tinged with brown or red blood. While the bloody show indicates the cervix is changing, it does not reliably predict the exact start of labor, as it can occur days or weeks before true contractions begin.
The rupture of the amniotic membranes, commonly referred to as the “water breaking,” is a more definitive sign of labor, even if contractions have not yet started. This presents as a sudden gush of fluid or a slow, continuous trickle. The amniotic fluid is typically clear or straw-colored, and its release means the protective sac around the baby has broken. If the water breaks, contact a healthcare provider immediately, as this carries an increased risk of infection, and labor usually follows within 24 hours.
How Healthcare Providers Assess Dilation
The only way to get a precise, numerical measurement of cervical dilation is through a manual, internal check performed by a healthcare provider. This procedure is known as a digital cervical exam. The provider inserts one or two gloved fingers into the vagina to feel the opening of the cervix and estimate its width in centimeters.
Dilation is measured on a scale from 0 to 10 centimeters (cm); 0 cm means the cervix is completely closed, and 10 cm represents the full dilation necessary for the baby to pass. The provider also assesses effacement, which is described as a percentage from 0% (thick and long) to 100% (paper-thin). Findings are often communicated as a combination, such as “3 cm dilated and 50% effaced.”
The digital exam provides a measurable snapshot of labor progress, though it is an estimate since finger size can vary slightly between practitioners. This measurement is generally taken when a person arrives at the hospital with regular contractions or if there is concern about labor progress. The dilation number is only one piece of information and is considered alongside the strength and frequency of contractions and the baby’s position in the pelvis.
Benchmarks: Understanding the Stages of Dilation
The first stage of labor, which involves the entire process of cervical change, is divided into three distinct phases based on dilation benchmarks. The Latent Phase is the longest and earliest part of labor, spanning from 0 cm to about 5 or 6 cm of dilation. During this time, contractions are often mild and irregular, allowing most people to comfortably remain at home while the cervix softens and thins.
Once the cervix reaches approximately 6 cm, labor progresses into the Active Phase. Contractions become noticeably stronger, more consistent, and closer together, typically prompting the move to a hospital or birth center. The Active Phase continues until dilation reaches 8 cm, with the cervix expected to open at a more predictable rate.
The final and most intense part of the first stage is the Transition Phase, spanning from 8 cm to the full 10 cm of dilation. Contractions during this phase are usually at their peak intensity and are very close together, often with little rest in between. Achieving 10 cm of dilation signifies the cervix is fully open and 100% effaced, marking the end of the first stage of labor and the beginning of the pushing stage.