The process of childbirth requires the cervix, the muscular neck of the uterus, to open or dilate. This opening is the most important metric healthcare providers use to measure progression through labor. While a medical examination is the definitive way to determine dilation, the body often provides observable signs that indicate cervical change is starting. Recognizing these physical changes helps prepare an individual for the stages of labor.
Physical Indicators of Dilation
One of the earliest indications of cervical change is the loss of the mucus plug. This plug is a collection of thick, jelly-like material that seals the cervical opening during pregnancy, acting as a protective barrier against infection. When the cervix softens and begins to open, the plug is dislodged and released from the vagina.
The loss may happen all at once as a single glob of discharge, or gradually over several days. This discharge is often clear, yellowish, or pink-tinged, and its appearance does not mean labor is imminent, as it can occur weeks before true labor begins. A related sign is the “bloody show,” which is blood-streaked mucus resulting from tiny blood vessels rupturing as the cervix thins and opens. The bloody show strongly indicates that cervical changes are occurring and the body is preparing for labor.
A person might also notice a sensation of tightening or cramping in the abdomen or lower back. These feelings are contractions, which are the muscular efforts of the uterus working to thin and open the cervix. Increased pelvic pressure is also common as the baby’s head descends lower into the pelvis, a process sometimes called lightening. These physical signs suggest the cervix is dilating, but they do not provide a precise measurement of progression.
Professional Assessment of Cervical Change
The only objective way to determine the exact degree of dilation is through a digital cervical examination performed by a healthcare provider. During this exam, two gloved fingers are inserted to feel the opening of the cervix. The measurement is expressed in centimeters (cm), running from 0 cm (closed) to 10 cm, which is considered fully dilated.
The provider simultaneously assesses two other factors important for determining labor progression: effacement and station. Effacement refers to the thinning and shortening of the cervix, measured in percentages from 0% (long and thick) to 100% (completely thinned out). The cervix typically needs to be nearly 100% effaced before it can fully dilate.
The third measure, station, describes how far the baby has descended into the pelvis relative to the ischial spines. Station is measured in numbers ranging from -5 to +5. Zero station means the baby’s presenting part, usually the head, is level with the ischial spines, indicating engagement. Negative numbers mean the baby is higher in the pelvis, and positive numbers mean the baby has moved below the spines. These three measurements—dilation, effacement, and station—are assessed together to give a complete picture of the cervix’s readiness for birth.
Differentiating Labor Contractions
Contractions are the force that drives cervical change, but not all contractions cause dilation. It is important to distinguish between true labor contractions and Braxton Hicks contractions, often called false labor. True labor contractions are effective because they are organized, regular, and progressively increase in frequency, duration, and intensity.
Unlike true labor, Braxton Hicks contractions are irregular, less painful, and usually cause discomfort only in the front of the abdomen. A key difference is that Braxton Hicks contractions often subside or disappear with a change in activity, such as walking, resting, or drinking water. True labor contractions, however, persist and intensify regardless of positional changes or hydration.
Effective labor contractions follow a consistent pattern, lasting between 30 and 70 seconds and becoming closer together over time. These rhythmic uterine tightenings thin and open the cervix, moving the person from the early, latent phase into the active phase where dilation accelerates. Accurately timing the contractions—noting the start, end, and interval between them—is important for determining progression toward active labor.
When Immediate Medical Attention is Necessary
While many signs of early dilation can be safely monitored at home, certain symptoms require immediate contact with a healthcare provider or a trip to the hospital. One clear threshold is when contractions occur regularly and follow a specific pattern, such as the 5-1-1 rule or similar guidelines recommended by the provider. This typically means contractions are about five minutes apart, lasting one minute each, and have been consistent for at least one hour.
Another definitive sign is the rupture of membranes, commonly known as the water breaking, which can be experienced as a sudden gush or a slow, continuous trickle of fluid. The healthcare provider should be contacted immediately if the membranes rupture, regardless of whether contractions have started. Prompt medical attention is also necessary for any significant, heavy vaginal bleeding—more than the light spotting associated with bloody show—or if there is a noticeable decrease in the baby’s usual movement.