Cervical dilation is the fundamental process that measures the progression of childbirth, representing the opening of the cervix, which is the lower part of the uterus. For a baby to successfully move from the womb into the birth canal, this muscular opening must widen significantly. Dilation is measured in centimeters, starting from zero and progressing to the maximum required width. The goal of the first stage of labor is to reach 10 centimeters of dilation, which is considered complete and allows the baby’s head to pass through the pelvis.
Early Cervical Changes Before Labor
The body often begins preparing for labor by initiating subtle changes in the cervix well before regular contractions start. This preparatory phase frequently involves cervical effacement, which is the thinning and softening of the cervix. Effacement is often a precursor to dilation, as the cervix needs to thin out before it can fully open.
It is common for some pregnant women to be partially dilated—often 1 to 3 centimeters—for days or even weeks without being in active labor. This slow, early opening is sometimes referred to as the prodromal or latent phase of labor. For women who have given birth previously, the cervix may begin to dilate earlier than in a first pregnancy.
Minor contractions that do not progress to true labor, known as Braxton Hicks contractions, may contribute to this early, slight dilation and effacement. These contractions are generally irregular and non-painful, but their gentle pressure can encourage initial cervical changes. However, minor dilation alone is not a reliable indicator for predicting when true labor will begin.
Dilation During Active Labor Phases
The true, sustained progression of cervical dilation begins once active labor is established, typically defined as the point when the cervix is dilated to about 6 centimeters. Before this point, the latent phase is characterized by slower, sporadic changes, moving from 0 to 6 centimeters over a long period. Once the active phase begins, contractions become stronger, more regular, and more effective at applying pressure to the cervix.
The rate of dilation generally accelerates once a woman is in the active phase of labor. For a first-time mother, a progression rate of approximately 1 centimeter per hour is commonly observed. Women who have previously delivered often experience a faster rate of change. This predictable progression is what healthcare providers track closely to ensure labor is advancing as expected.
The final stage of the first phase of labor is called the transition phase, covering the period from about 8 centimeters to the full 10 centimeters of dilation. This phase is usually the most intense, characterized by the strongest and most frequent contractions. Reaching 10 centimeters signifies complete dilation, marking the end of the first stage and the beginning of the second stage, when pushing begins.
How Dilation is Measured and Monitored
Cervical dilation is assessed by a healthcare provider using a manual cervical examination, often called a finger check. The provider inserts two gloved fingers into the vagina to physically feel the opening of the cervix. They estimate the diameter of the opening in centimeters, using the width of the fingers as a reference scale.
The measurement is reported as a single number from 0 to 10 centimeters, where 0 indicates a closed cervix and 10 indicates a fully open cervix. This 10-point scale is the standard metric used to track progress through the first stage of labor. Effacement is also measured during this examination, reported as a percentage ranging from 0% (thick) to 100% (fully thinned).
While dilation measurement is important for monitoring labor progress, checks are not performed constantly. Healthcare providers typically assess dilation upon hospital admission and then every four to six hours during the active phase of labor. Minimizing the frequency of these checks helps reduce the risk of infection and allows the laboring woman to rest. The goal is to confirm safe progression toward full dilation.