Cervical dilation is the opening of the cervix, the lower, narrow part of the uterus that connects to the vagina. This process is necessary for childbirth, as the cervix must widen to allow the passage of the baby into the birth canal. Dilation is considered the primary measure of progression during labor, marking the body’s readiness for delivery.
Observable Symptoms Indicating Dilation
The first noticeable physical sign that the cervix is changing is often the loss of the mucus plug, sometimes called the “bloody show.” This thick mucus seals the cervical opening during pregnancy. As the cervix softens and starts to open, the plug is dislodged and discharged from the vagina, sometimes appearing tinged pink or brown with blood.
While the loss of the mucus plug suggests cervical change is underway, it does not reliably predict when labor will begin. A more definitive sign is the rupture of the amniotic membranes, commonly called the “water breaking.” This release of amniotic fluid can manifest as a sudden gush or a steady trickle, indicating that labor is imminent.
Another common symptom is a noticeable increase in pressure felt deep in the pelvis or lower back. This sensation occurs because the baby has moved lower into the birth canal, known as “lightening,” and the head is pressing against the cervix. These symptoms indicate a progressing cervix but do not confirm the exact degree of opening, which requires a medical examination.
The Mechanics of Cervical Measurement
The precise extent of cervical opening is measured clinically using a digital examination performed by a healthcare provider. This internal examination involves the provider inserting two gloved fingers into the vagina to manually assess the opening. The measurement is expressed in centimeters, ranging from zero (completely closed) to ten (fully dilated).
Full dilation at 10 centimeters is the point at which the cervix is wide enough for the baby’s head to pass through. This milestone must be reached before the pushing stage of labor can begin. Providers also track effacement, which is the thinning and shortening of the cervix, normally long and firm during pregnancy. Effacement is measured in percentages, where 0% means the cervix is thick and 100% means it has become paper-thin. Dilation and effacement are interdependent and typically happen concurrently; the goal for vaginal delivery is a cervix that is 100% effaced and 10 centimeters dilated.
Identifying True Labor Contractions
Contractions are the uterine muscle tightening and relaxing, which is the physical force causing the cervix to dilate and efface. Distinguishing true labor contractions, which cause cervical change, from Braxton Hicks contractions (false labor), is a helpful step in determining labor progression. True labor contractions follow a pattern, becoming progressively more regular, stronger, and longer over time.
Unlike false labor, true labor contractions will not stop or ease up with a change in activity, such as walking, resting, or drinking water. True contractions often radiate from the back and move toward the front of the abdomen, lasting between 30 and 70 seconds each. Braxton Hicks contractions, in contrast, are irregular, remain mild, and are often felt only in the front of the abdomen.
A common guideline for when to contact a healthcare provider is the “5-1-1 rule,” which describes a pattern typical of active labor. This rule suggests seeking medical assessment when contractions are coming every five minutes, lasting for one minute each, and following this consistent pattern for at least one hour. While monitoring the pattern is a strong indicator, only the physical cervical exam can definitively confirm the extent of dilation achieved.