Cervical dilation is a fundamental process in childbirth, representing the opening of the cervix as the body prepares for delivery. This physiological change is a key indicator of labor progression. Understanding cervical dilation and its associated signs can help expectant parents recognize when labor may be approaching.
Understanding Cervical Dilation
Cervical dilation refers to the widening of the cervix, the lower part of the uterus that connects to the vagina. This opening is measured in centimeters, ranging from 0 cm when completely closed to 10 cm when fully dilated for vaginal birth. As the cervix dilates, it also undergoes a process called effacement.
Cervical effacement is the thinning and shortening of the cervix, measured in percentages from 0% (no thinning) to 100% (paper-thin). During pregnancy, the cervix is typically long and firm, but as labor nears, it softens, thins, and shortens. Both dilation and effacement work together to prepare the birth canal for the baby’s passage.
Another important measurement during labor is fetal station, which describes how far the baby’s head has descended into the pelvis. This is measured in relation to bony points in the pelvis called the ischial spines, with 0 station indicating the baby’s head is aligned with these spines. Negative numbers, such as -5, mean the baby is higher in the pelvis, while positive numbers, like +5, indicate the baby is lower and nearing birth.
Recognizing Potential Signs of Labor
Several signs and symptoms may suggest cervical changes and the onset of labor. One common indicator is the presence of contractions, which are the tightening and relaxing of the uterine muscles. True labor contractions typically become progressively stronger, longer, and closer together, unlike Braxton Hicks contractions, which are often irregular and may subside with a change in activity or position.
Another potential sign is “bloody show,” which is the discharge of blood-tinged mucus from the vagina. This occurs as the cervix begins to soften, thin, and widen, causing small blood vessels to tear and mix with the mucus plug that sealed the cervix during pregnancy. While bloody show suggests cervical changes are happening, it does not necessarily mean labor will begin immediately; it can appear hours or even days before active labor.
The rupture of membranes, commonly known as “water breaking,” is another significant sign. This can manifest as a sudden gush or a slow trickle of fluid from the vagina. The amniotic fluid, which cushions the baby, should generally be clear and odorless, though it may be slightly blood-tinged. Other less specific signs include persistent back pain, pelvic pressure, or cramping, which can accompany the cervical changes and uterine activity of early labor.
How Dilation is Professionally Assessed
The definitive method for assessing cervical dilation, effacement, and fetal station is through a vaginal examination performed by a healthcare provider. During this examination, the provider inserts sterile, gloved fingers into the vagina to manually feel the cervix. They estimate the cervical opening in centimeters, the thinning in percentages, and the baby’s position relative to the pelvic landmarks.
While a digital exam is the standard, a transvaginal ultrasound may sometimes be used for a more precise measurement of cervical changes, though this is less common. Self-checking for dilation is not recommended due to the potential risk of introducing infection and the difficulty in accurately assessing these subtle changes without professional training.
When to Contact Your Healthcare Provider
It is important to contact a healthcare provider when certain labor signs become apparent to determine the appropriate next steps. If contractions become regular, strong, and consistently closer together, such as lasting about one minute, occurring every five minutes, for at least an hour, it is typically advised to call. These patterns suggest active labor may be progressing.
Contact your provider immediately if your water breaks, even if contractions have not yet started. Note the fluid’s color and odor; clear and odorless fluid is typical, but green, brown, or foul-smelling fluid requires urgent attention as it could indicate a complication. Any significant vaginal bleeding that is more than just light spotting or bloody show, especially bright red bleeding, also warrants immediate medical consultation.
A noticeable decrease in fetal movement is a concern that requires prompt medical evaluation. If you observe your baby moving less than usual, or if you cannot feel at least 10 movements within a two-hour period, contact your healthcare provider right away. Always follow your individual provider’s specific instructions for when to seek care, and do not hesitate to reach out with any concerns or uncertainties, especially if you are less than 37 weeks pregnant.