Cervical dilation tracks the progress of labor. This process involves the cervix softening, thinning, and opening to allow the baby to pass into the birth canal. Dilation is measured in centimeters, starting at zero when the cervix is closed and reaching ten centimeters when it is considered fully dilated, or “complete.” The goal of the first stage of labor is to achieve this ten-centimeter opening. Understanding the signs of this cervical change can help a person prepare for childbirth, though only a healthcare provider can confirm the exact measurement.
Physical Indicators of Cervical Change
Several noticeable changes indicate the cervix is softening and beginning to open, signaling the start of labor. One common sign is the occurrence of uterine contractions, which are the rhythmic tightening and relaxing of the uterine muscles. True labor contractions are distinct from Braxton Hicks, or practice contractions, because they become progressively longer, stronger, and closer together over time. Unlike the irregular and mild Braxton Hicks contractions, true labor contractions will not stop or ease up when a person changes position or rests.
Another physical sign that the cervix is softening and dilating is the appearance of the “bloody show.” This discharge results from the loss of the mucus plug, a thick collection of mucus that seals the cervical opening during pregnancy. As the cervix starts to efface and open, this plug is released, appearing as a thick discharge that may be clear, pink, or tinged with brown or red blood. While the bloody show indicates cervical changes are occurring, it is not a precise measure of dilation and can happen anywhere from a few hours to a few weeks before active labor begins.
The rupture of membranes, commonly known as the “water breaking,” is a definitive indication of labor or the imminent need for medical attention. This happens when the amniotic sac surrounding the baby breaks, releasing the fluid. It may be experienced as a sudden gush or a steady trickle that is usually odorless and clear or straw-colored. The onset of contractions typically follows the rupture, but the timing varies greatly among individuals.
How Healthcare Providers Measure Dilation
The only way to definitively know the centimeter measurement of cervical dilation is through a vaginal examination performed by a medical professional. During this procedure, the provider inserts one or two gloved fingers into the vagina to physically assess the cervix. They approximate the width of the cervical opening with their fingers to determine the measurement in centimeters. This method is subjective, meaning the measurement can vary slightly depending on the individual provider performing the examination.
Dilation is one of three measurements a provider assesses to determine the full picture of labor progression. They also evaluate effacement, which is the thinning and shortening of the cervix, measured in a percentage from 0% (thick) to 100% (paper-thin). The cervix must be 100% effaced before a vaginal delivery can occur, as this thinning allows the opening to expand fully. Both dilation and effacement constitute cervical ripening, the process where the cervix prepares for birth.
The third measurement is the fetal station, which describes the position of the baby’s head relative to the mother’s pelvis. Station is measured in centimeters, with zero indicating the baby’s head is level with the ischial spines. Negative numbers (-5 to -1) mean the baby is higher up in the pelvis, while positive numbers (+1 to +5) indicate the baby is further descended into the birth canal. Assessing dilation, effacement, and station helps the healthcare team determine how smoothly labor is progressing.
Defining the Stages of Labor Progression
The first stage of labor is divided into two phases: the latent phase and the active phase. The latent phase is characterized by slow cervical dilation, ranging from zero to six centimeters. Contractions during this time are often irregular and mild, feeling like menstrual cramps or a dull backache. This phase is the longest and least predictable, often lasting many hours, and is frequently managed at home.
The active phase begins when the cervix is dilated to about six centimeters and continues until full dilation at ten centimeters. Contractions become stronger, longer, and more frequent, typically occurring every three to five minutes. The rate of cervical change becomes more rapid and predictable during this stage, often dilating at a pace of one to one and a half centimeters per hour. Hospital admission is recommended once a person has entered the active phase of labor.
The transition phase is the final, intense part of the active phase, covering dilation from eight to ten centimeters. Contractions are at their peak intensity, often lasting 60 to 90 seconds and coming every two to three minutes. This phase is physically and emotionally demanding but is usually the shortest, signaling that delivery is near. Once the cervix reaches ten centimeters, labor progresses to the second stage, and the person can begin pushing.