The final weeks of pregnancy involve significant physical changes signaling the start of labor. The cervix, a cylinder-shaped tissue connecting the uterus to the vagina, must transform to allow birth. Understanding cervical dilation and recognizing the physical signs that accompany this change provides clarity. This guide details the progression of cervical change and how to interpret the body’s signals as it prepares for delivery.
Defining Cervical Change and Measurement
Cervical change involves two distinct processes: dilation and effacement. Dilation is the opening of the cervix, measured in centimeters, which must expand from zero (closed) to ten centimeters (fully dilated) for a vaginal birth. This widening is primarily driven by the strength and frequency of uterine contractions pushing the baby downward.
Effacement is the complementary process, describing the thinning and shortening of the cervix. During pregnancy, the cervix is long and firm, but as labor approaches, it softens and thins out, measured in percentages from zero to one hundred percent. A cervix that is 100% effaced is described as being paper-thin, having completely shortened into the uterine wall. Both full dilation and full effacement are necessary before the pushing stage of labor can begin.
Recognizable Physical Signs of Labor
The most reliable indication of cervical dilation comes from contractions that follow a predictable pattern. True labor contractions are distinct from practice contractions, known as Braxton Hicks, because they consistently become longer, stronger, and closer together over time. True labor contractions do not stop when you change activity or rest, and they often cause pressure in the lower back or abdomen.
A visible sign of cervical change is the loss of the mucus plug, a thick, jelly-like collection of secretions that seals the cervical canal during pregnancy. As the cervix softens and begins to open, this plug is expelled and may appear clear, yellowish, or tinged with pink, brown, or red blood. Losing the mucus plug does not guarantee immediate labor, as it can be shed days or weeks before active labor begins.
The “bloody show” is a related, more definitive sign of imminent labor. This discharge is blood-streaked mucus resulting from small blood vessels in the cervix rupturing as the tissue dilates and thins. The bloody show indicates that the physical changes of the cervix are actively progressing, often meaning labor is relatively close, sometimes within hours or a couple of days.
Another sign is the rupture of membranes, commonly called the “water breaking,” which can occur as a sudden gush or a steady trickle of fluid. This means the amniotic sac surrounding the baby has opened, and it is an indication to contact a healthcare provider immediately, regardless of contractions. The fluid should be noted for its color and odor, as this information is important for the medical team.
How Healthcare Providers Check Dilation
The only way to confirm the exact measurement of cervical dilation and effacement is through a digital cervical exam. During this exam, a healthcare provider wears sterile gloves and inserts one or two fingers into the vagina to manually feel the cervix. They use their fingers to estimate the width of the opening, which is reported in centimeters.
The provider also assesses effacement by determining the thickness and position of the cervix. They also note the baby’s “station,” which describes how far down the baby’s head is positioned within the pelvis. These internal checks are performed during the final weeks of pregnancy and are repeated throughout active labor to monitor progress.
The measurement is an estimate based on the examiner’s finger width and can vary between providers. The exam confirms if true labor is underway and guides decisions about the next steps in the labor process. While the exam is a standard tool, it is not always necessary, and patients can discuss the timing and frequency of these checks with their medical team.
Knowing When to Contact Medical Help
A common guideline for when to contact your healthcare provider or head to the hospital is the “5-1-1 rule.” This rule suggests labor is progressing when contractions are five minutes apart, each lasting one minute, and this pattern has been consistent for at least one hour. Some providers may suggest a “4-1-1” rule, especially for those who live far from the hospital or have a history of fast labor.
You should contact your medical team immediately if your water breaks, even without regular contractions. Any vaginal bleeding heavier than light spotting or bloody show, or any reduction in the baby’s usual movement, also warrants an immediate call. If any signs of labor begin before 37 weeks of pregnancy, contact a provider immediately, as this may indicate premature labor.